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Synthesis of Hydrophilic Radical Polymers and their Application to an Organic Secondary Battery 親水性ラジカルポリマ K
Page 1
Synthesis of Hydrophilic Radical Polymers and
their Application to
an Organic Secondary Battery
親水性ラジカルポリマーの合成と有機二次電池への展開
A Thesis
Presented to
Waseda University
July 2009
Kenichiroh KOSHIKA
小鹿 健一郎

Page 2
Promoter:
Prof. Dr. Hiroyuki Nishide
Referees:
Prof. Dr. Takayuki Homma
Assoc. Prof. Dr. Kenichi Oyaizu

Page 3
iii
Preface
Research on devices for electrical energy storage has currently received significant
attention. Rechargeable or secondary batteries, such as lithium ion batteries, are very
popular and being used in portable electronic devices, such as mobile phones, laptop PCs,
and digital cameras, and could also be used in electric vehicles, for electric storage and in
solar- and wind-energy converters. Secondary batteries have been regarded as an
environmentally benign technology because of their rechargeability which contributes to
reducing the amount of discarded primary batteries. However, secondary batteries still
remain immature from the view points of green chemistry, i.e., limited metal resources,
tedious waste treatment processes, and safety concerns.
Many researchers have explored new electrode-active materials to solve above issues.
The author proposed hydrophilic radical polymers and their energy storage applications,
which allowed the battery design with heavy metal-free. The battery was expected to show
an improvement charging-discharging performance and green benign characteristics.
In this thesis, the author describes synthesis and electrochemical properties of
hydrophilic radical polymers which demonstrated rapid charging and long cycle life.
Chapter 1 reviews radical polymers and their battery applications. Chapter 2 describes
synthesis and electrochemical properties of TEMPO substituted polyvinylether. Chapter 3
deals with the performance of a semi-organic model radical polymer battery utilizing with
zinc anode. Chapter 4 describes safety assessment of radical polymers for electrode-active
materials. Chapter 5 deals with organic model radical polymer battery utilizing with
viologen polymer-anode and its green character evaluation. Chapter 6 describes synthesis
and electrochemical properties of TEMPO substituted polyacrylamide. The final chapter
concludes this thesis and proposes the future prospects of hydrophilic radical polymers.
Kenichiroh Koshika

Page 4
iv
Synthesis of Hydrophilic Radical Polymers and
their Application to
an Organic Secondary Battery
親水性ラジカルポリマーの合成と有機二次電池への展開
Contents
Preface
Chapter 1 General Introduction
1.1 Introduction
….. 3
1.2 Current Situations and Issues of Secondary Batteries
….. 4
1.3 The Twelve Principals of Green Chemistry and Practice in Design of
Organic Secondary Battery
…. 17
1.4 Radical Polymers for Electrode-Active Materials
…. 24
Chapter 2 Synthesis and Electrochemical Properties of TEMPO Substituted Polyvinylether
2.1 Introduction
…. 40
2.2 Synthesis of the TEMPO Substituted Polyvinylether
…. 41
2.3 Electrochemical Properties of the TEMPO Substituted Polyvinylether
…. 43
2.4 Cathode Performance of the TEMPO Substituted Polyvinylether
…. 46
2.5 Experimental Section
…. 49
Chapter 3 Redox Properties of TEMPO Substituted Polyvinylether on Aqueous Electrolyte
Conditions and its Battery performance of Test-Cell Fabricated with Zinc Anode
3.1 Introduction
…. 54
3.2 Redox Properties on pH
…. 55
3.3 Redox Properties on variety of salts Redox Properties on Salt Concentration
…. 56
3.4 Redox Properties on Variety of Salts
…. 57
3.5 Battery performance of the Test-Cell Fabricated with Zinc Anode
…. 61
3.6 Experimental Section
…. 62

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v
Chapter 4 Safety Assessment s of the Radical Polymers for Battery Electrode
4.1 Introduction
…. 66
4.2 Cathode Performance Evaluation
…. 68
4.3 Disaster Safety Assessment
…. 67
4.4 Health Safety Assessment
…. 69
4.5 Experimental Section
…. 72
Chapter 5 Battery Performance and Green Evaluation of Organic Secondary Battery Fabricated
with Radical Polymers and Aqueous Electrolyte
5.1 Introduction
…. 76
5.2 Synthesis of Viologen Polymer for Anode-Active Material
…. 77
5.3 Electrochemical Properties of Viologen Polymer
…. 78
5.4 Battery Performance of the Organic Secondary Battery
…. 80
5.5 Green Evaluation for the Organic Secondary Battery
…. 82
5.6 Experimental Section
…. 87
Chapter 6 Synthesis and Electrochemical Properties of TEMPO Substituted Polyacrylamide
6.1 Introduction
…. 92
6.2 Synthesis of the TEMPO Substituted Polyacrylamide
…. 93
6.3 Electrochemical Properties of the TEMPO Substituted Polyacrylamide
…. 94
6.4 Cathode Performance of the TEMPO Substituted Polyacrylamide
…. 95
6.5 Battery Performance of the Organic Secondary Battery
…. 99
6.6 Experimental Section
... 101
Chapter 7 Conclusion and Future Prospects
7.1 Conclusion
... 106
7.2 Future Prospects
... 108
List of publications
Acknowledgements

Page 6

Page 7
Chapter 1
General Introduction
1.1 Introduction
1.2 Current Situations and Issues of Secondary Batteries
1.3 The Twelve Principals of Green Chemistry and Practice in Design of Organic Secondary
Battery
1.4 Radical Polymers for Electrode-Active Materials
References

Page 8

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Introduction
- 3 -
1.1 Introduction
Chemistry toward sustainable society—Green sustainable chemistry has been recognized
as an important technology. In the battery industry, mercury-free design manganese battery
and alkaline battery have been developed as environment compatible batteries. Secondary or
rechargeable batteries such as lithium ion battery and nickel hydrogen battery have become
popular as eco-friendly battery. Especially secondary batteries have been widely used in
portable electronic devices such as mobile phone, digital camera and laptop PC, being
required high performance such as capacity, charging-discharging rate performance and long
cycle life. On the other hand, many researchers have studied and explored new energy storage
material which allow above battery performance as another approach. Some organic materials
have a redox ability which is able to apply as electrode active material. Radical battery using
redox property of robust organic radicals as an electrode-active material is an organic based
secondary battery characterized by a high charging-discharging rate performance and long
cycle life. Radical polymers allowed charge transfer and storage due to their molecular design
composed of robust organic radical pendant with reversible and rapid redox ability.
In this thesis, the author tried to improve the charging-discharging rate performance and
reduce the risks of ignition and/or explosion accident at the same time by a combination of
radical polymer and aqueous electrolyte which possesses high electron conductivity and no
flammability. Previously reported radical polymers had a lipophilic character, utilizing in not
aqueous electrolytes but organic electrolytes. This low compatibility between lipophilic
radical polymer and aqueous electrolyte led to reduce the charging-discharging capacity with
insufficient compensation of counter ions. Therefore aqueous electrolyte-type radical polymer
battery has never been reported. The author designed and synthesized a series of hydrophilic
radical polymers which were highly subsisted robust radicals with a stable redox property in
ambient condition and water, to improve the low compatibly for aqueous electrolytes. Redox
properties of radical polymer in aqueous electrolyte were systematically studied for
application toward a high performance organic based secondary battery characterized rapid
charging, long cycle life, and high safety.
This thesis was composed of seven chapters as follows: (1) prolegomenon, (2) synthesis
and electrochemical property of TEMPO substituted polyvinylether, (3) effect on electrolyte
conditions for redox property and an application for semi-organic model test cell, (4) safety
assessment of radical polymers, (5) an application for organic model test cell using
polyviologen anode, (6) synthesis and electrochemical property of TEMPO substituted
polyacrylamide for battery application and (7) conclusion and future perspective.

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Chapter 1
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1.2 Current Situations and Issues of Secondary Batteries
1.2.1 Introduction
Secondary batteries have been widely used in portable devices, such as portable phone,
digital camera and laptop PC. Lead battery was also used in motor vehicles all over the world.
The Japanese market for batteries was approximately 846.1 billion JPY in 2008. Secondary
batteries occupied 85% of the total amount of sales. Especially lithium ion battery and nickel
metal-hydride battery occupied more than 60% of the total amount of sales. Many researchers
and engineers have been improve their battery performance and have tried to apply to energy
resource of motor vehicles replacing lead battery.
1.2.2 Conventional Secondary Batteries
The battery performance, such as output voltage, capacity density and rechargeable
number was almost derived from a combination of electrode-active materials. The
components and performance of the secondary batteries such as nickel-cadmium battery,
nickel metal-hydride battery and lithium ion battery were reviewed.
Nickel-cadmium
The Ni-Cd is by far the most robust rechargeable battery system and can deliver very high
power pulses (greater than 15 C), withstand overcharge, overdischarge, and function down to
–40°C. In 1977, it was the only small sealed rechargeable battery and was produced with both
pressed powder and sintered electrode in vented and sealed sinter constructions.[1] The sinter
electrode constructions are being slowly replaced by higher capacity structures such as a
felted nickel fibril electrode structure. A similar open nickel foam structure has been
developed by vapor depositing nickel from nickel carbonyl into a bed of urethane foam
spheres, and then burning off the polymer.[2] The vented Ni-Cd system dominates the
commercial jet aircraft applications just as the valve-regulated lead acid dominates the
civilian aircraft and automotive applications. The sinter has about 80% porosity to
accommodate the active materials. The felted and foam electrode constructions with 90 to
95% porosity contain about 10 to 15% more active material with a concomitant increase in
capacity but lower rate capability. The shift to polymer-bonded cadmium electrodes has
practically eliminated the severe environmental issues of dusting during cell fabrication for
Ni-Cd.
McBreen has summarized nickel hydroxide materials used in Ni-Cd and Ni-MH
batteries.[3] The reaction scheme of Bode[4] still prevails, but with a better understanding of
the structure of the various materials and their interactions.[5] Spherical Ni(OH)2 materials
have been developed with better packing efficiency to increase cell capacity.[6, 7] Additives to
control oxygen evolution during charge yield higher capacity and prolong storage life. The

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Introduction
- 5 -
European Economic Community threat to ban Ni-Cd batteries in Europe by 2008 has
adversely impacted Ni-Cd sales to the benefit of Ni-MH. The industry is active in developing
recycling operations for Ni-Cd, similar to those in place for lead acid, to counter this threat.
Nickel metal hydride
The Ni-MH is a modification of the Ni-Cd technology where the cadmium electrode is
replaced by a hydrogen storage alloy. The improvements in the nickel cathode described
above in the Ni-Cd section, translate directly to the Ni-MH system. The Ni-MH cell reaction
shown below had
MH +2NiOOH = Ni(OH)2 + 1/2H2
its origin with the invention of hydrogen absorbing metals in the 1970s.[8] Two series of alloys,
lanthanum-nickel based (AB5)[9]
and titanium-zirconium based (AB2)[10]
have been
developed. Each of the series of alloys has additives to improve corrosion resistance, cycle
life, lower cost, etc. Some compositions have so many additives that they are referred to as
kitchen sink alloys. Although the AB2 alloys have higher hydrogen storage capability, the
AB5 alloy system has been preferred for commercial Ni-MH cell because of its good
mechanical stability, better low temperature, and high-rate performance.
Commercial production of the Ni-MH system started about 1990 driven by the need to
replace Ni-Cd in portable electronics with smaller, higher performance rechargeable batteries.
The change from cadmium to hydrogen storage alloy anode allows a different cell design and
electrode balance than Ni-Cd with a doubling in capacity for the same size cell. As a result,
Ni-MH has considerably higher energy storage capacity than Ni-Cd. The Ni-Cd and Ni-MH
cell constructions are identical except that the hydrogen absorbing metal anode replaces
cadmium. The Ni-MH is made on the same Ni-Cd cell assembly equipment using a
polymer-bonded hydrogen alloy powder as the anode. This permits a shift to Ni-MH with a
minimum of capital investment. The Ni-MH is the battery of choice for the developing hybrid
electric vehicle applications
Lithium ion battery system (Li-ion)
The Li-ion battery is an enabling technology for a new generation of portable electronic
devices. There are several excellent reviews of the technology and its development.[11-14]
There is no lithium metal in the battery. Lithium is found only in ionic form in solution and in
an atomic state when intercalated into the carbon anode or the oxide cathode materials. A
carbon, capable of intercalating lithium, replaced the metallic lithium anode that has defied
cycling for any extended period. Sony first commercialized the Li-ion system shortly after the

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Chapter 1
- 6 -
publication by Tazawa and Nagaura[15] who described the first commercial cell, its
construction, and its performance. Asahi Chemical also made an effort to develop the
technology. The elements of electrochemical intercalation into carbons and graphites was
established by Besenhard[16] and used in a rechargeable cell by Basu.[17] Goodenough et al.[18]
established the reversible lithiation of cobalt, manganese, and nickel oxides that are used in all
Li-ion cells. For the first time, the energy storage capability of a rechargeable system
approached that of the primary battery systems. The cell reactions for manganese and cobalt
cathodes are
Li0C + LiCoO2 = LixC + Li1-xCoO2
Li0C + LiMn2O4 = LixC + Li1-xMn2O2
The Li-ion cells are assembled in the discharged state. The source of lithium for the anode is
the cathode. The first charge of the cell transfers lithium from the cathode to the anode.
Lithium cobalt oxide is the active cathode material of choice although lithium manganese
spinel and lithium nickel oxide are being used. The cobalt material delivers about a 145
mAh/g working capacity and may be doped with Al, Mg, etc., to stabilize its structure against
oxygen evolution.[19] The mixed oxide LiNi0.8Co0.2O2 has a higher capacity (about 190
mAh/g) and is more stable than the pure nickel oxide. The manganese cell discharges at a
higher voltage (3.7 V vs. 3.6 V for cobalt) but has a lower capacity (about 115 mAh/g). The
manganese is lower in cost and is more stable against oxygen evolution but is susceptible to
acid leaching by HF produced from the hydrolysis of residual water in the LiPF6
electrolyte.[20] Li-ion cells, especially those with low cost manganese cathodes, are being
developed and used for electric and hybrid vehicles with capacities of 90 Ah or more.[21, 22]
Large Li-ion cells have been space-qualified by SAFT in Europe.
In addition to cobalt and manganese materials, lithium iron and vanadium phosphates are
now used as cathode materials in commercial Li-ion polymer cells. These offer the possibility
of lower cost, while providing greater stability for longer life and safety.[23-25] The materials
discharge at a lower voltage (3.4 V) but have a reasonable capacity (140 mAh/g) near that for
the cobalt compounds.
Commercial Li-ion batteries mainly use graphite or hard carbon materials. Dahn reviewed
the various carbon anode materials for use in Li-ion batteries.[26-28] Hard carbons (cokes) have
a longer cycle life but lower capacity (about 270 mAh/g) and higher first cycle loss than do
graphites. When fully charged, all carbon materials approach to within 50 mV from the
reversible lithium potential. New higher capacity tin alloy[29] and lithium cobalt nitride[30]
based anodes are under development with the potential of reaching over 700 mAh/g useful
capacity.

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Introduction
- 7 -
Just as with lithium metal batteries, the solid electrolyte interface (SEI) layer forms
spontaneously on the carbonaceous anode of a Li-ion cell during first charge.[31, 32] Once
formed, the film protects the solvent and polymers from further reaction with the
carbon-lithium anode. This film formation is the key element to stable battery performance.
The composition of the SEI film has been the subject of considerable speculation. Recently,
studies on pure, clean, lithium surfaces have shed considerable light on the composition of the
SEI layer during its formation.[33, 34] To eliminate contamination, all experiments were carried
out in high vacuum and the reaction products were identified by infrared spectral analysis.
The common cyclic and linear organic carbonate electrolyte solvents react to form the
corresponding lithium alkoxides.[35]
The high cell voltage restricts the choice of organic solvents for the electrolyte.[36, 37]
Generally, cyclic and linear carbonates are the materials of choice as they are stable to
reduction by lithium and against oxidation to above 4.5 V vs. Li. In the electrolyte, LiPF6 is
preferred as the salt for its higher conductivity over LiBF4, and a solvent combination of a
cyclic carbonate (ethylene carbonate, etc.) coupled with linear carbonate materials (dimethyl
carbonate, diethyl carbonate, ethyl methyl carbonate, etc.). Each manufacturer has its own
preferred electrolyte composition.
Propylene carbonate cannot be used with graphitic anodes as it intercalates into the
anodes on charge. Two new solutes are under development to replace the LiPF6 and eliminate
HF formation from hydrolysis. Oestand et al.[38] have substituted two alky groups for two of
the fluorine atoms in PF for better stability. The other is lithium bisoxalatoborate (LiBOB).[39]
This salt requires reformulation of the solvent composition for good performance.
Electrolyte additives such as vinylene carbonate form stable films that reduce the amount
of lithium used in the SEI formation and improve storage life.[40] Other additives are added as
a safety measure to activate the current interrupt devices (CID) device. These compounds
have a tertiary hydrogen atom, such as cyclohexyl benzene and biphenylcarbonate, are
electroactive, and generate hydrogen gas around 4.5 V vs. Li/Li+. If a cell should be
overcharged above the normal 4.2 charge voltage, when the cell voltage reaches 4.5 V, the
compound reacts to generate hydrogen gas. The internal gas pressure increases rapidly to
activate the CID and disconnect the cell from this abusive condition.
Typical Li-ion cell construction (for example, Panasonic model) is shown in Figure 1.1.1.
The designs of all cell manufacturers incorporate safety devices such as shutdown separators,
pressure vents, CIDs and positive temperature coefficient (PTC) resistors to protect against
abuse conditions from external shorts. In addition, electronic power management and safety
circuitry measures temperature, current, and voltage during cell operation. All manufacturers
insist on temperature, voltage, and current control to limit cell operation within safe bounds
and to avoid damage to the active materials. Li-ion cells have the capability to self-destruct if

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Chapter 1
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the operation is not controlled.
The Li-ion cell design employs a thin microporous polyolefin separator, usually
polyethylene, of the order of 50% porosity. The pores are about 400 Å in diameter. The pores
close up to increase internal cell resistance and stop cell action when the separator reaches
about 110°C (termed a shut-down separator). The cell case is nickel-plated steel but thin
lightweight aluminum cans are used to reduce the weight.
Safety is a key issue with the Li-ion cell system. Cells for commercial use are required to
pass safety testing programs such as that of the UL Laboratories and the UN and DOT
shipping regulations. The cells are protected against external abuse by the devices described
above along with the electronic power management units incorporated in all battery packs.
While a good part of safety resides in the internal cell design, the reactivity of the electrolyte
also plays a role. Thermal runaway in Li-ion batteries occurs when the electrolyte
spontaneously reacts directly with the active cathode and anode materials. Reactivity with
anode and cathode active materials with the electrolyte determines the onset of thermal
runaway conditions.[41] These reactions initiate at about 130°C and start with the destruction
of the SEI layer on the anode. The reactions are autocatalytic and quickly send the cell into
thermal runaway where it destructs. Temperatures in this range can result from internal cell
shorts or exposure to high temperature environments.
Figure 1.2.1 Constructions of cylindrical Li-ion cells
1.2.3 Lithium-ion battery hazards
Apart from the fact that lithium batteries have highly oxidizing and reducing materials,
their safety is compounded by the fact that the design of these non-aqueous cells has an
inherent drawback of poor heat dissipation. Compared to lithium metal-anode batteries,
lithium-ion cells are considered to be safer. The redox potentials of metallic lithium and
lithiated carbons (LixC6), for example, are similar. The reactive surface area of the
carbonaceous anode with a typical particle size of about 10 μm is large. Although the specific
surface area of the lithiated carbon electrode has been demonstrated to increase by a factor of

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Introduction
- 9 -
five upon cycling[42], the reactivity of anode is kinetically limited by the slow transport of
lithium from the galleries to the surface of the graphitic electrode.[43-45] Another important
factor that contributes to enhanced safety of lithium-ion battery vis-à-vis lithium metal anode
batteries is the much higher melting point of LixC6 as compared to that of lithium metal. The
low melting point of lithium (180°C) poses an additional risk of fire hazard from molten
lithium generated by inadvertent over-heating. However, exothermic reactions between and
LixC6 andthe electrolyte can be triggered by the application of heat.[46, 47]
The potential ranges experienced in common 4-V lithium ion cells are beyond the
thermodynamic stability windows of the electrolytes. Electrolytes, therefore, decompose upon
contact with the charged active materials, both anode[48-53] and cathodes[54-58]. The interface
between the cathode and electrolyte is further complicated by partial dissolution of the
positive active materials.[59-61] This is particularly a problem at the end of charging and at
elevated temperature, conditions under which electrolyte oxidation can proceed at accelerated
rates.[44, 59, 62-66]
The temperature of a cell is determined by the heat balance between the amount of heat
generated and that dissipated by the cell. When a cell gets heated above a certain temperature
(usually above 130–150°C), exothermic chemical reactions between the electrodes and
electrolyte sets in, raising its internal temperature. If the cell can be dissipated, the exothermic
processes would proceed under adiabatic-like conditions and the cell’s temperature will
increase rapidly. The rise in temperature will further accelerate the chemical reactions, rather
than the desired galvanic reactions, causing even more heat to be produced, eventually
resulting in thermal runaway,[43, 67, 68] whose onset temperature determines the safety limit of
the device. Any pressure generated in these processes can cause mechanical failures within
cells, triggering short circuits, premature death of the cell by irreversible interruptions in the
current path, distortion, swelling and rupture of casing.
It is clear that the thermal stability of batteries depends on its ability to dissipate the heat.
The ability of an object to absorb heat is defined by its thermal capacity. Obviously, for a
given amount of heat, bigger and heavier objects would suffer less temperature rise than
would a similar object that is smaller and lighter. Thus, for lithium-ion batteries, which are
designed for applications where size and weight are a premium, a decrease in the thermal
capacity is an unavoidable penalty. Thus, heat dissipation in lithium-ion batteries turns out to
be a major engineering challenge, especially for those designed for high power applications.
Designs for effective heat dissipation must be adopted both at the cell and battery pack levels.
Heat dissipation can occur by convection and radiation at the surface of the cell. Heat
dissipation by convection depends, among other things, on the external surface area and
geometry of the cell. However, heat dissipated by radiation depends on the nature of the
surface of the cell and makes up nearly 50% of the dissipation.[69] Radiation dissipation can be

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Chapter 1
- 10 -
improved by use of cell cases that have high thermal conductivity and labels that have high
emissivity. Thermal performance is rarely a cause for cell failure in low-power cells that have
simple designs. However, thermal design of high-power cells is not that simple. Poor designs
can result in localized hotspots within the cell, which can lead to cell failure.
Possible exothermic reactions that trigger thermal runaway include[68, 70]: (i) thermal
decomposition of the electrolyte; (ii) reduction of the electrolyte by the anode; (iii) oxidation
of the electrolyte by the cathode; (iv) thermal decomposition of the anode and cathode; and
(v) melting of the separator and the consequent internal short. Moreover, high-voltage metal
cathodes are known to release oxygen at elevated temperature.[71, 72] Thermal runaway is often
caused under abuse conditions, which can be thermal (overheating), electrical (overcharge,
high pulse power) of mechanical (crushing, internal or external shot circuit).[68, 73]
It must be noted that the release of materials from batteries can be benign, mild or violent.
Battery hazards are classifies according to the damage they cause.[67] Physical hazards involve
a simple rupture of battery case; chemical hazards result from leakage or benting of corrosive
or toxic materials in the battery; both chemical and physical hazards can cause equipment
damage due to breakage or corrosion of electrical/electronic components; environmental
hazards arise from the reactive and flammable nature of lithium and/or leakage of toxic
materials from batteries that are improperly disposed.
An area that has often been over looked is the possible embrittlement of container metal
with lithium (similar to hydrogen embrittlement). This can happen if the metal in question is
capable of alloying with lithium. In such a case, a spontaneous transfer of lithium to the
alloying metal casing can occur.[74] This can lead to a structural destruction of the container
material, resulting in leakage paths. Lithium embrittlement at highly stressed refions of
battery containers can accelerate crack propagation. Although lithium battery leakages have
been observed, no conclusive evidence is available to merit extensive research in this
direction.
Figure 1.2.2 Ignition mechanism of lithium-ion battery.

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Introduction
- 11 -
1.2.4 Conventional safety devices
A predominant mechanism by which lithium batteries are rendered safe involves limiting
the current passing through them. Current-limiting device such as positive thermal coefficient
devices are designed are designed to respond to high temperatures. Several factors play a role
in the operation of these devices: the ambient temperature, thermal insulating properties of the
container, heat generated in the equipment, cumulative heat in the battery pack, and rate and
duration of discharge. Thus, it becomes necessary to consult the manufacturer or conduct tests
in order to determine the suitability of a battery pack for a particular application.
Apart from preventing flow of excessive current-limiting protection devices must
withstand continuous flow of the load’s design current and tolerate normal surges and
transients. Furthermore, safety devices must also fit into very small spaces and must be
relatively cheap. For acceptance in commerce, the current-limiting device must be fail-proof,
which also means that it should not be prone to false tripping, factors that can decide
customer dissatisfaction. It must be pointed out that batteries regulated with external
electronic devices such as PTC elements and integrated circuits would not only have lighter
manufacturing cost but also lower energy density.
Safety vents
Conventional safety mechanisms include such devices as vents and current-limiting
devices like fuses and circuit breakers. Safety vents open in response to a sudden increase in
cell pressure, allowing gases to escape. If the pressure inside a cell builds up, a plastic
laminate membrane is punctured by a spike incorporated in the vent in the cell top. A safe
release of internal pressure precludes dangerous rupture of the cell casing. Safety vents can be
designed to operate at pre-set internal cell temperatures. Today, vents are a back-up safety
device. During instances of electrical abuse, other devices such as a positive temperatures
coefficient device (described below) override the vent. If batteries are subjected to severe
mechanical abuse conditions, the safety vent provides a means of releasing internal pressure
and prevents the cell from reaching excessively high temperatures.
Kato et al.[75] developed a safety mechanical link by which a concave aluminum disk
welded to the cathode would break the circuit upon release of gas. In this design, lithium
carbonate deliberately added to the LiCoO2 cathode mix would decompose to yield CO2 when
the cell is overcharged to greater than 4.8 V. The built-up pressure would push the aluminum
disk, disconnecting the cathode lead from the circuit. This simple mechanism prevents the cell
from the thermal runaway caused by an excessive overcharge. Choi et al.[76] have shown that
in addition to providing safety, the added lithium carbonate can suppress the initial
irreversibility of the carbon anode.
Since the safety vent opens up the cell, spewing out a significant quantity of volatile

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Chapter 1
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organics, it is used as a back-up safety ride the safety vent during abuse. Under severe
mechanical and electrical abuse conditions, the bent provides a safe means of releasing
internal pressure before the cell reaches excessively high temperatures.
Thermal fuses
The oldest and most common current limiter is the one-shot fuse, which is a wire of a
fusible alloy with resistance and thermal characteristics that allow it to melt when a pre-set
current flows through it. Some fuses require several seconds to trip, but they are inherently
fast-acting. The advantages of the fuse as a safety device lie in its simple construction, low
cost and availability in a wide range of currents and voltages ranges. Fuses act by destroying
themselves, thereby positively and permanently opening the circuits they protect. Thus they
must be replaced once blown, which is another advantage (as it draws the attention of the user
to take action for resuming service) although the mechanical action involves labor. However,
fuses can prematurely blow under other conditions such as pulse discharges (or repeated pulse
discharges that can degrade the alloy), which are normal operational modes of batteries.
Moreover, there is the possibility of inadvertent replacement with fuse with higher or lower
current ratings, which can result in improper use of equipment. Fuses are wired in series with
the cell stack and will open when a pre-set cell temperature is reached. Thermal fuses are
employed as protection against thermal runaway and are usually set to open at 30–50°C above
the maximum operating temperature of the battery. Fuses are cheap and are ideal for low-cost,
throwaway product with limited warranties.
Other circuit breakers
Other circuit breakers such as magnetic switches, bimetallic thermostats and electronic
protection circuit modules can be used to protect power packs and to monitor their
temperature. They must also tolerate continuous design current as that of the load as well as
occasional current surges, without tripping. However, their size and cost often rule out the
application of the first two in many onboard circuits, especially where space is at a premium.
Thermistors sense the internal temperature of the battery, and provide information to an
external control through a calibrated resistance. Thermistor controls may be located in battery
charger. The Thermistor is attractive as the control can be set to meet specific conditions of
charge and to regulate input current to the battery. This device can also be used to control the
battery through ∆T/∆t control, where T and t are the temperature and time, respectively PTC
Thermistors have a positive temperature coefficient, as will be described below. Similarly,
Thermistors whose resistance decreases with increasing temperature are called negative
temperature coefficient (NTC) Thermistors. Both are used for monitoring and protection of
control circuits.

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Introduction
- 13 -
The thermostat or temperature cut-off (TCO) devices operate at a fixed temperature, and
can be used to terminate charge (or discharge) when a pre-set internal battery temperature is
reached. TCOs are usually resettable. They are connected in series with the cell stack.
Electronic safety circuits, commonly referred to as protection circuit module (PCM), are
usually attached to battery packs as separate modules. In the event of a wrongful condition,
such as short circuit, the PCM opens the battery circuit and prevents damage to the pack.
Some groups believe that the cell chemistry in lithium-ion cells can be modified and safety
levels rose rendering PCMs redundant.[77]
Unlike aqueous electrolyte cells, which have an inherent balance-adjusting mechanism
such as gas recombination, lithium-ion cells require an external overcharge/overdischarge
protection system, particularly those for use in specialized applications as in electric traction
and spacecraft. This can be provided through an electronic control circuit. However, the cost
component of the circuits is kept small as compared to the cost of the batteries themselves.
The basic circuitry consists of a bypass circuit controlled by a microchip based on MOS-FET.
The bypass circuit gets activated when a cell in a pack reaches a given state-of-charge,
electronic controllers can be designed to sense voltages and, thereby, switch on or off the
charging/discharging circuit. This ensures charge balance among cells in a pack and damage
by overcharge/overdischarge of individual cells. In specialized applications, battery packs
come with protection circuits that monitor cell temperature and activate cooling gadgets such
as fans.
1.2.5 Developed safety devices
Shutdown separators
Separators for lithium-ion batteries are polyolefin microporous films and are generally
uniaxially drawn polyethylene (PE) and polypropylene (PP), biaxially drawn PE or
multi-axially drawn PP/PE/PP.[78] In addition to conventional characteristics such as good
mechanical strength, electrolyte permeability, these microporous separators display a
protective property during cell abuse. For example, if the cell temperature rises abnormally
because of an excessive overcharge, for example, the heat generated softens PE and closes the
micropores in the film. This is called separator “shutdown”.[79, 80] Once shutdown occurs,
ionic transport between the electrodes is effectively stopped and current ceases to flow.[80] If
the separator can retain mechanical integrity above its shutdown temperature, it can provide a
margin of safety to the device; otherwise, the electrodes can come into direct contact, react
chemically, leading to thermal runaway. However, it is possible that due to thermal inertia the
temperature can continue to rise even after shutdown. Under such conditions the separator
would melt and short the electrodes, leading to violent reactions and heat generation. This
phenomenon is called “meltdown” or “breakdown” of the separator. Therefore, in order to

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ensure safety of the cell, the difference between the “shutdown” and “meltdown”
temperatures should be as large as possible.
Separators made entirely of high-density polyethylene melt at 135 °C and lose
mechanical integrity above this temperature. However, separators made by laminating layers
of polypropylene and polyethylene maintain mechanical integrity at least up to 165 °C, the
melting point of polypropylene. It is interesting to note that although ultrahigh molecular
weight polyethylene melts at 135 °C, separators made from this material retain their
mechanical integrity up to at least 180 °C as the viscosity of the material is such that it
maintains physical integrity. Shutdown separators are reliable and lithium-ion battery
manufacturers are increasingly opting for their incorporation in their products. The most
common shutdown separators have high molecular weight polypropylene blended with
super-high molecular weight polyethylene.[77] Here, the unique shutdown property of
polyethylene is combined favorably with the high mechanical integrity of polypropylene at
elevated temperatures. Because the shutdown is irreversible, once actuated, these separators
leave the cells permanently damaged.
Electrolytes
The key to a safe high-performance lithium-ion cell lies in the identification of a suitable
electrolyte. Lithium is intrinsically unstable with any commonly known electrolyte. Moreover,
lithium battery electrolytes based on alkyl carbonate solvents are known to react vigorously at
elevated temperatures with lithiated graphite and delithiated cathodes (e.g., LixCoO2 (x <
0.5)).[53, 81-83] At elevated temperatures, the SEI on the graphite anode gets destroyed, allowing
rapid and direct reaction with the lithiated graphite underneath the passivating layer. In their
delithiated forms, cathodes are highly oxidizing and enter into exothermic reactions with alkyl
carbonates, especially at elevated temperatures. Careful calorimetric studies have thus become
mandatory to determine the safety of electrode–electrolyte combinations. According to
Aurbach et al.[84], commonly used electrolytes such as LiPF6 in EC–DEC–DMC are only a
compromise. They are flammable and their electrochemical windows are limited to about 4.5
V. Alternatives to such alkyl carbonate solvents are not on the horizon although alternative
salts such as lithium bis(oxalato)borate, LiBC4O8
(LiBOB),[85]
and lithium
fluoroalkylphosphates (e.g., Li[PF3(C2F5)3])[86-88] are being considered in place of LiPF6.
Aurbach et al.[84] suggest that under the circumstances, it is only prudent that additives that
can protect electrode-active materials even at high temperatures by forming highly protective
films on the electrodes be investigated. In fact, new formulations of solvents and salts are
unveiled continually with an eye on safety and performance. A number of additives are also
being investigated to make up for problems due to protective films at the positive and
negative electrodes. Additives have also been sought to lower electrolyte flammability under

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cell venting. Redox couples that shuttle back and forth as additives to limit overcharge and
additives that produce gas for activating current interrupter devices have also attracted
interest.
Active materials
Commercial lithium-ion batteries are thermally stable up to 60 °C,[89] above which their
performance declines. Anode/electrolyte reactions occur first,[90] while cathode/electrolyte
reactions dominate the heat-evolution processes at elevated temperatures.[53] The latter if
allowed to progress can be hazardous. Violent reactions are known to occur in the charged
state of lithium-ion batteries. In fact, although lithiated carbon anodes are considered safer
than metallic lithium anodes,[43] at large values of x in LixC6 (x ~1 for graphite) they can react
with the electrolyte under abusive conditions, releasing heat. Similarly, at small values of x in
LixCoO2, LixNiO2 and LixMn2O, the cathodes can adversely influence their thermal stability.
[44, 91] Therefore, thermal studies on negative electrodes are performed in their lithiated state
and positive electrodes in the delithiated state. Because cell temperatures during abuse
reactions can melt the aluminum current collector but not the copper current collector,
Biensan et al.[92] conclude that cell temperatures should reach between 659 °C (mp of Al) and
1083 °C (mp of Cu).
Carbon anode
The composition of the SEI on graphite depends on the electrolyte composition and
strongly affects the onset temperature for thermal reactions at the graphite anode.[93-95] While
the composition of the SEI is dictated more by the salt in the case of electrolytes with LiBF4
and LiPF6, the solvent takes a prominent role with electrolytes containing salts such as
LiCF3SO3 and LiN(SO2CF3)2.[96] Thermal reactions at salt-based SEIs proceed via surface salt
decomposition, yielding mainly LiF.[97] On the other hand, thermal reactions in predominantly
solvent-based SEIs proceed via decomposition of lithium-alkyl carbonates to Li2CO3.[96] For
this reason, the latter type of SEIs is thermally more stable. Thermal stability of salt-based
SEIs can be improved by controlling reactions involving salts complexing their anions with
anion acceptors.[98-101] Besides, anion acceptors increase lithium-ion diffusion and transport
number by suppressing ion-pair formation. In fact, Herstedt et al. [102]showed that the addition
of tris(penta-fluorophenyl)borane (TPFPB) to LiBF4–EC–DEC improves the cyclability and
raises the thermal stability of graphite anodes by as much as 60 °C.
DSC and ARC studies have shown that carbon anodes cycled in carbonate-based
electrolytes undergo exothermic reactions between 60 and 200 °C.[53, 103-105] Components of
the SEI on MCMB cycled in LiPF6–EC–DMC have been shown to be the source of an
exothermic reaction below 100 °C,[103] while above 100 °C intercalated lithium is believed to

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participate in the thermal reactions. According to Menachem et al. [105]a chemically bonded
SEI formed by mild oxidation of graphite suppresses exothermic reactions and has a lesser
tendency to ‘peel off’ from the anode during heating. In an exciting discovery, Jiang and Dahn
[106] found that the addition of LiBOB to EC–DEC significantly improved the thermal stability
of LiC6. LiBOB is believed to form a robust SEI on lithiated carbon surface, preventing any
exothermic process until 170 °C as compared to an onset temperature of 80 °C with
LiPF6–EC–DEC.[106]
LiCoO2
LixCoO2 is thermally unstable and can decompose, releasing oxygen at elevated
temperature[70, 107-109] according to the reaction[44]
Li0.5CoO2 → 0.5LiCoO2 + 1/6CoO + 1/6O2
The released oxygen can then react with organic solvents to generate heat. By ARC, Jiang
and Dahn [110] showed that organic solvents can reduce Li0.5CoO2 (the normally fully charged
composition) to Co3O4 and CoO, eventually even to Co metal and that the reactivity of
LixCoO2 in electrolyte can be affected by particle size, surface area, electrolyte composition,
etc.[110, 111] MacNeil et al.[82] reported that the first thermal processes between LixCoO2 and
electrolyte can be described by an auto-catalytic reaction. In fact, the reaction of Li0.5CoO2
with EC–DEC begins at 130 °C, which is much lower than the decomposition temperature of
Li0.5CoO2 itself.[107] Baba et al.,[109] who evaluated the thermal stability of chemically
delithiated LiCoO2 (Li0.49CoO2) by DSC, the active cathode decomposed the electrolyte at
190 °C, the mechanism of which may be written as follows for EC [107]:
Li0.5CoO2 + 0.1C3H4O3 (EC) → 0.5LiCoO2 + 0.5CoO + 0.3CO2 + 0.2H2O.
A DSC peak at 230°C is ascribed to the oxidation of the electrolyte caused by oxygen
released from Li0.49CoO2.[109] Jiang and Dahn [110] showed that the reactivity of Li0.5CoO2 was
higher in LiBOB–EC–DEC than in LiPF6–EC–DEC. The lower stability of the LiBOB-based
electrolyte must be seen in the backdrop of the fact that the LiBOB can effectively stabilize
the SEI of LiC6. This means that graphite/LiCoO2 cells cannot be rendered safer by replacing
LiPF6 with LiBOB in the electrolyte.

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1.3 The Twelve Principles of Green Chemistry
1.3.1 Introduction
Green chemistry, environmentally benign chemical synthesis, alternative synthetic
pathways for pollution prevention, benign by design: these phrases all essentially describe the
same concept. Green chemistry is the utilization of a set of principles that reduces or
eliminates the use or generation of hazardous substances in the design, manufacture and
application of chemical products.
Recent years, Green chemistry has been paid much attention. This is because there has
been much debate over the past generation over the exact nature of the environmental hazards
that have been generated as a result of the release of various synthetic chemicals into the
environment. There is little doubt that until the uncertainties in the toxicological data –
exposure, fate, and transport data – and the risk analyses are unequivocally resolved, this
debate will continue, probably for at least the next generation. Therefore, there are two logical
choices left to the scientific community. The first is to allow the uncertainties described above
to continue to be paralyzing and not to attempt to address the concerns for human health and
the environment. The second option, which those pursuing the new area of green chemistry
have adopted, is to accept the fact that the release of chemicals to the environment causes
some incremental increase in the risk to human health and the environment. The risk can be
eliminated through fundamental breakthroughs in chemical methodologies that are technically
and economically viable, then the chemical community should pursue it.
It is as a true in green chemistry as it is in every other area of science that one can only
operate with the current state of knowledge, but, with the knowledge of chemical hazards that
now exists, chemists can aim to minimize them.
1.3.2 Fundamental molecular science providing the root risk reduction
Researchers at the vanguard of innovation in this new area know that these goals can be
accomplished. While everyone understands that no activity can be completely risk free, the
goals achieved both at the research bench and in commercialized processes have greatly
decreased environmental and health concerns, while developing efficacious process and
methodologies.
Yet another reason for the chemistry community to pursue green chemistry vigorously is
because it is based on fundamental molecular science providing the root of the solution, rather
than on applying a bandage or patchwork approach to risk reduction. At its most basic level,
risk can be described by the following formula in Figure. 1.3.1.
The traditional way that industry and society, through national environmental policy, has
dealt with the reduction of risk is through the reduction of exposure. With a fixed hazard and a

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reduced exposure, risk should decrease proportionately. By using well-characterized hazards
(toxicity data) and knowing the efficacy of whatever exposure control method is being used,
the risk can be manipulated until it is below some identifiable, acceptable level. This
‘acceptable level’, by necessity, has to be arbitrary since the question of ‘acceptable to
whom?’ must then be faced.
While a 1:1 000 000 cancer risk from exposure to a certain level of a substance may be
defined by society in its laws and regulations as ‘acceptable’, it certainly is not acceptable if
you are that ‘1’ in 1:1 000 000.
Another limitation of exposure controls to reduce risk is that the use and release of a
chemical may affect individuals who aren’t using those controls. For instance, a chemical may
affect individuals who aren’t using those controls. For instance, a chemical worker may be
wearing gloves, goggles, etc. in order to protect themselves from being exposed to high levels
of a certain substance known to have acute effects. But how do these exposure controls affect
someone downstream or downwind who is not protected by exposure controls. With
uncertainties with chronic effect, bioaccumulative effects, and synergistic effects being
extremely high for a broad range of substances under the current status of the science, the use
of exposure controls to reduce risk to society in general is called into question.
A final reason why exposure controls may be limited is because they can fail. No
respirator, face shield, glasses, gloves, goggles, or protective suit is perfect. With failure of
this exposure-limiting equipment, the individual is then at maximum risk from the hazard.
Contrast the above limitations to the hazard-reducing principles of green chemistry. The
largest difference between the two approaches to risk reduction is that hazard reduction
through green chemistry, when done properly, cannot fail. If, through the variety of techniques
and methodologies that will be discussed in this book (e.g. alternative feedstock, solvents) the
hazard is reduced, there is no way that the risk can increase through a spontaneous increase in
the hazard. In other words, there is no way that an innocuous substance is going to become
arbitrarily toxic to human health and the environment. Now, of course, in the same way that
someone could put safety goggles on backwards or put protective rubber gloves on their feet,
it is equally conceivable that green chemistry can be performed incorrectly. This would be
equivalent to substituting an extremely toxic substance for one that is virtually non-toxic.
Beyond this absurd exception, hazard reduction through green chemistry must necessarily
reduce risk. Also, in contrast to the use of exposure controls to reduce risk, the effect of
exposure on downstream of downwind recipients of the chemical hazard is less. Because the
intrinsic nature of the substance itself is less hazardous, there is no differential risk to the
person working with the substance versus the secondarily exposed individual. Finally, the
concept of a level of acceptable risk is eliminated as a target and replaced with the optimal
goal of environmentally benign. While more will be said on this topic later, the goal of

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making a chemical product or process ‘environmentally benign’ is a mere statement of the
ethic of continuous improvement more than it is a metric by which to measure improvement.
It is because of the reasons outlined above that the approach to risk reduction through
utilization of hazard reduction via green chemistry is preferable to that via exposure control.
From an economic standpoint, one fact is intuitively obvious. There is not a chemical
product or process that is going to be more economically favorable because of the need for, or
use of, exposure controls. Regardless of the methods or equipment used, form engineering
controls to personal protective gear, there is always an associated cost and that means an
economic drain. More will be said on this subject when the full costs of risk reduction are
addressed later in this chapter.
In contrast, a green chemistry solution to risk reduction could, potentially, have a variety
of economic benefits associated with its implementation. Some possibilities include lower
feedstock costs, higher conversion rates, shorter reaction time, greater selectivity, enhanced
separations, or lower energy chemistry solution is going to have these benefits, these potential
economic gains stand juxtaposed to the certain economic drains of exposure controls. It
should be noted that the advantages of green chemistry listed relate to direct operating costs.
Additional indirect cost advantages will also be discussed later.
Risk = f (hazard, exposure)
Figure 1.3.1 Formula describing risk.
1.3.3 The twelve principles of green chemistry
The listing of the ‘Twelve Principles of Green Chemistry’ which proposed by Paul T.
Anastas and John C. Waner, should be viewed as a reflection of the science that has been done
within this nascent field in the recent past, as well as direction that has been set by some of
the pioneering scientists who have laid the ground work for the future.
1. It is better to prevent waste than to treat or clean up waste after it is formed.
2. Synthetic methods should be designed to maximize the incorporation of all
materials used in the process into the final product.
3. Wherever practicable, synthetic methodologies should be designed to use
and generate substances that possess little or no toxicity to human health and
the environment.
4. Chemical products should be designed to preserve efficacy of function while
reducing toxicity.

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5. The use of auxiliary substances (e.g. solvents, separation agents, etc.) should
be made unnecessary wherever possible and, innocuous when used.
6. Energy requirements should be recognized for their environmental and
economic impacts and should be minimized. Synthetic methods should be
conducted at ambient temperature and pressure.
7. A raw material of feedstock should be renewable rather than depleting
wherever technically and economically practicable.
8. Unnecessary derivatization (blocking group, protection /deprotection,
temporary modification of physical/chemical processes) should be avoided
whenever possible.
9. Catalytic reagents 8 as selective as possible) are superior to stoichiometric
reagents.
10. Chemical products should be designed so that at the end of their function
they do not persist in the environment and break down into innocuous
degradation products.
11. Analytical methodologies need to be further developed to allow for
real-time, in-process monitoring and control prior to the formation of
hazardous substances.
12. Substances and the form of a substance used in a chemical process should be
chosen so as to minimize the potential for chemical accidents, including
releases, explosions, and fires.
1.3.4 Applying the Twelve Principles for Organic Secondary Battery Design
In this section, the author selects six principles which were considered highly important
to design organic secondary batteries and explains their details and practice in battery design.
Principle 1: ‘It is better to prevent waste than to treat or clean up waste after it is formed.’
This principle suggested chemists regard dealing with hazardous substances as costs. The
costs of dealing with hazardous substances, either through handling, treatment, or disposal,
have continued to increase substantially. These costs will now have to be factored in unless
they are prevented. The only way to prevent these costs arising is to avoid the use or
generation of hazardous substances by designing chemistry through the use of green
chemistry techniques.
The battery design was required to be composed of lower toxic and hazardous materials.
Conventional lithium-ion battery contains flammable organic solvent as an electrolyte solvent

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with built in safety system such as, separator, PTC circuit, and inflammable additives. Radical
polymer battery was also contained organic solvents for electrolyte of the battery. To reduce
the ignition and/or explosion accident, the electrolyte should be replaced by aqueous
electrolyte.
Principle 2: ‘Synthetic methods should be designed to maximize the incorporation of all
materials used in the process into the final product.’
This principle proposed chemists understand that perfectly efficient synthesis according
to the percentage yield calculation could generate significant amounts of waste. The classic
evaluation of the effectiveness and efficiency of a synthesis is yield. Yield also totally ignores
the use or generation of any undesirable products that are an intrinsic part of the synthesis. To
solve this issue, atom economy was developed. Atom economy is an assessment in which one
looks at all of the reactants to measure the degree to which each of them is incorporated into
the final product.
The synthetic scheme for electrode-active polymer also should be designed to maximize
the incorporation of all materials used in the process into the final product. We should
recognize the effect of 4 reactions on atom-economies: rearrangements, addition, substitution
and elimination.
(1) Rearrangements—by definition, a rearrangement reaction is a reorganization of the
atoms that make up a molecule. Therefore, by necessity, it is a 100% atom
economical reaction, where all the reactants are incorporated into the product.
(2) Addition―Because addition reactions add the element of the reactant to a substrate
with total inclusion (e.g. cycloadditions, bromination of olefins) they are atomic
economical.
(3) Substitution―When a substitution reaction is effected, the substituting group
displaces a leaving group. The leaving group is necessarily a waste product of the
reaction that is not included in the final product and therefore diminishes the atom
economy of the transformation. The exact degree to which the reaction is non-atom
economical is dependent on the specific reagents and substrates used.
(4) Elimination―Elimination reactions transform the substrate by reducing the atoms to
generate the final product. In this case, any reagents used do not become part of the
final product and the eliminated atoms are lost as waste. This is, therefore,
intrinsically the least atom economical of the basic synthetic transformations.
Principle 3: ‘Wherever practicable, synthetic methodologies should be designed to use and
generate substances that possess little or no toxicity to human health and the environment.’
This principle insists that the fundamental basis of green chemistry is the incorporation of
hazard minimization or elimination into all aspects of the design of chemistry. There is an

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intrinsic need to consider hazard when designing chemistry for the environment. There are
only two ways to minimize risk of harm of any kind: either minimize the exposure or
minimize the hazard. Minimizing exposure can take a variety of forms, such as protective
clothing, engineering controls, respirators, etc. Minimizing the hazard can be achieved by
chemist. They can easily manipulate molecules to make them difficult or impossible to be
absorbed through biological membranes and tissues. By eliminating the absorption and
bioavailability, toxicity is concurrently decreased. Therefore, as long as the change in the
properties to make the molecule less bioavailable does not impair the intended function and
use of the molecule, it will be both efficacious and less toxic.
The materials which are used and generated by reaction should be controlled and
recognized their hazardous potentials. Generally polymers are considered to be non-toxic and
low potential risks causing health hazards. The polymers are nonvolatile and insoluble for
general solvent, i.e. the polymers had low possibility to enter the human body through the
respiratory tract and skin. On the other hand, raw materials for polymers have a potential risk
of hazards for health. Therefore toxic potential of these materials should be investigated.
Principle 4: ‘Chemical products should be designed to preserve efficacy of function while
reducing toxicity.’
This principle recommended chemists should design safer chemicals using several basic
approaches. The design of safer chemicals is now possible because there have been such great
advances in the understanding of chemical toxicity. The mechanisms of action of substances
on the body and in the environment were identified by many researches. By knowing the
mechanism in detail, chemists can then modify the structure so that these reactions are no
longer possible, thereby reducing toxicity.
In this point, polymer electrode was considered to be highly effective. Polymer electrodes
are considered to be non-toxic and low potential risks causing health hazards. he polymers are
nonvolatile and insoluble for general solvent, i.e. the polymers had low possibility to enter the
human body through the respiratory tract and skin.
Principle 5: ‘The use of auxiliary substances (e.g. solvents, separation agents, etc.) should
be made unnecessary wherever possible and, innocuous when used.’
This principle insisted importance of selection of auxiliary substances. In the manufacture,
processing and use of chemicals, there are auxiliary substances used at a every step. An
auxiliary substance can be defined as one that aids in the manipulation of a chemical or
chemicals, but is not an integral part of the molecule itself. The use of these substances is
designed to overcome specific obstacles in the synthesis or production of a molecule or
chemical product. Many auxiliary substances have come into such widespread use that there
is seldom an evaluation as to whether or not they are necessary. This is true of solvents in

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many cases, as well as for separation agents for many operations. Often, these auxiliaries can
possess properties that are of concern for human health and the environment.
The auxiliary substances should be dialed with as the one of the most careful handling
materials. The polymer synthesis process required much amount of organic solvents for
reaction and separation comparing main products. The one of the advantages of polymer
electrode over inorganic electrode was easy disposal and low impact for environment.
However the issues of much material consumption in synthesis process have been remained.
Optimization material consumption for polymer synthesis will improve the green
characteristics.
Principle 12: ‘Substances and the form of a substance used in a chemical process should be
chosen so as to minimize the potential for chemical accidents, including releases,
explosions, and fires.’
This principle encourage chemists prevent chemical accident. The importance of accident
prevention in chemistry and the chemical industry cannot be overstated. There have been a
number of notable chemical accidents that have resulted in the mobilization of public option
to control the use of chemicals. The accidents have resulted in the loss of hundred of human
lives. The hazards posed by toxicity, explosively, and flammability all need to be addressed in
the design of chemical products and processes. The goals of green chemistry must involve the
full range of hazards and not be focused simply on pollution or ecotoxicity.
The organic electrolytes which utilized in radical polymer battery have a flammability,
remaining potential risk of ignition and/or explosion. This configuration requires
improvement to reduce the hazard risks.

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1.4 Radical Polymers for Electrode-Active Materials
1.4.1 Introduction
Rechargeable secondary batteries are widely used in portable equipments. Ubiquitous
electronic devices, such as smart cards, IC tags, and rollup displays, and power electric
instruments, such as electric vehicles and robots, and solar-energy and wind-power storage,
also require the development of secondary batteries. Among the secondary batteries, lithium
ion batteries are becoming the most popular: Almost 6 billion battery cells worth 8 billion
US$ were produced in Japan, in 2007,[112] which corresponded to almost half of the
world-wide production of Li-ion batteries.
The configuration of a conventional Li-ion battery is illustrated in Figure 1.4.1. The
cathode is composed of Li-ion-containing metal oxides, such as cobalt oxide, and the anode is
graphitic carbon; during the charging process, Li-ions are eliminated from lattice of the metal
oxide cathode and intercalated into the carbon anode. During the discharging process, the
lithium cobalt oxide is regenerated by the reduction reaction with Li-ions.[14] That is, the
Li-ion battery is based on the rocking-chair-typed intercalation reactions of Li-ions between
the cathode and anode materials. Li is the smallest among the elements except for hydrogen
and helium, and the very high electromotive force of the Li-ion (LixC→xLi+ + xe- + C: -2.9 V
vs. NHE) results in a high energy-density performance and the highest given voltage at the
battery. However, the intercalating diffusion of Li-ions accompanied by transformation of the
lattice- and layer-structure during the electrode reactions causes slow kinetics and heat
generation in the charging and discharging processes, sometimes producing overheating and
occasionally ignition. Indeed, in 2007 and 08 Panasonic and Sony encountered serious
recallings of their 46 and 0.1 million Li-ion batteries for mobile phones and laptops,
respectively, due to overheating accidents.[113, 114]
Figure 1.4.1 Scheme of a conventional Li-ion battery
The cathode- and anode-active materials of conventional primary and secondary batteries
are usually metal-oxides, such as manganese-, silver-, lead-, nickel-, and, vanadium-oxides,
and metals, such as zinc, lead, cadmium, and lithium.[115] That is, all the electrodes of

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conventional batteries are composed of such metals and metal oxides (except oxygen and
carbon for the air battery cathode and the lithium battery anode, respectively), some of which
come from limited resources.
Tedious waste processing of used batteries is another difficult and crucial issue of the
metal- and metal oxide-based conventional batteries. Used batteries are, in these days of
environmental concern, being collected and recycled. Among the recycling of used batteries,
the Li-ion batteries are highly valued for their excellent collection yield of 60% from personal
computers and mobile phones.[116] The typical recycle processing of used Li-ion batteries,
represented in Figure. 2, is reasonably working, at least in Japan, which includes several
steps.[117] The first step is incineration at high temperature to open the batteries and burn out
the electrolytes and separators. The residue is subsequently sieved and magnetically separated
to obtain the steel and copper. The remaining powder is dissolved in acid, and the solvent
extraction yields cobalt and other metal compounds. The recovered cobalt is re-introduced
into the production cycle of batteries. However, the collection yields of used Li-ion batteries
are somewhat decreasing because the batteries are being equipped in many varieties of small
devices. Additionally, other used batteries are often found in landfill disposal or simply stand
at the level at 60 kton/year even in Japan.[118] The conventional metal-based batteries involve
several inherent unsolved issues from the stand points of Green Chemistry.
Figure 1.4.2 Recycling of used Li-ion batteries in Japan
1.4.2 Robust Radical Molecules
Organic functional polymers have been developed as alternatives of inorganic functional
materials because of their light weight, flexibility, thin film-forming ability, processability,
metal-free or benign environmental aspects, and fewer limitations by organic resources.
Organic-derived electrode-active battery materials have been studied since the 1980s.
McDiarmid and Heeger by extending their discovery of electrically conductive polyacetylene,
reported in 1981,[119] the potential application of p- and n-doping processes in polyacetylene
to rechargeable batteries in an all-organic device design. However, the achievable doping
degree of polyacetylene was limited to less than 10% of the repeating units, which confined
the energy-density of the battery to a low value. The chemical instability of both the virgin

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and doped polyacetylenes was the fatal flaw to practically applying the polyacetylenes to a
battery device. In the late 1980s, disulfide compounds were intensively investigated as a
cathode material.[120] However, their rate performance remains low due to the bimolecular
redox reaction (2RS• ֕ RS-SR). Additionally, the nasty odor of sulfur compounds is a
problematic practical issue.
Our original plan to develop an organic polymer-based battery or a plastic battery using
organic electrodes is being achieved by focusing on and utilizing robust organic radical
molecules. The radical molecule is an organic molecular entity possessing one unpaired
electron, which often appears as an intermediate during photochemical and thermal reactions
and are also known to initiate and propagate polymerization and combustion reactions. They
are usually short-lived and highly reactive, thus the organic radicals had been classified as
unstable and intractable materials. However, organic radicals have been chemically modified
into stable or robust compounds, existing for appreciable lengths of time under ambient
conditions. Chemical stabilization has been achieved via sterically protected structures around
the radical centers or the unpaired electrons and/or by resonance structures involving the
unpaired electrons. Based on these chemical modifications, hundreds of stable organic
radicals are now known.[121]
Some robust radicals are commercially available and examples are shown in Figure. 3
(The dots symbolize an unpaired electron). They are widely used as spin labels for monitoring
biomolecules and as spin traps or radical scavengers of organic materials and biological
systems.
Figure 1.4.3 Commercially available robust organic radicals as a spin-label and spin-trap
Precursors of radical molecules are also produced in multi ton quantities as antioxidants
and as light-stabilizers for plastics and commodity materials (Figure 1.4.4). For example,

Page 33
Introduction
- 27 -
hindered amines (and polyamines) and hindered phenols (and polyphenols) act as antioxidants
to reductively remove oxygen and radical contaminants, yielding stable radical species
through the abstraction of hydrogen. In short, organic molecular radicals and their precursors
have been utilized in commodity materials and biomedical applications, and have been
examined and guaranteed as nontoxic materials.
Figure 1.4.4 Radical precursors as an antioxidants and a light-stabilizer
Robust organic radicals have also been extended to their polymeric radical analogs
(Figure 1.4.5). The radical polymers were extensively studied in the 1970s as redox reagents
or redox resins, which catalyze the oxidative and/or reductive reactions of organic compounds.
For example, poly(acrylate)-combined TEMPOs were synthesized and studied as a catalytic
reagent for the oxidation of alcohols into aldehydes and ketones (TEMPO:
2,2,6,6-tetramethylpiperidine-1-oxyl).[122] The organic radical-based or metal-free redox
reagents have been recently reexamined from the perspective of green or environmentally
compatible chemical reaction processes.
Figure 1.4.5 Nitroxide radicals as a redox catalyst
1.4.3 Electron-Transfer Process of Radical Polymers
Why do the radical polymers work as redox catalysts? Important electrochemical studies
have revealed that the nitroxide radical displays a reversible redox behavior attributable to the
one-electron oxidation of the nitroxide radical and reduction of the corresponding
oxoammonium to the original nitroxide (the left-hand reaction in Figure 1.4.6). This
reversible oxidation corresponds to the p-type doping of the radical material. On the other
hand, a phenoxyl radical is one-electron reduced to form the corresponding anion and
oxidized back to the phenoxyl radical (the right-hand reaction in Figure 1.4.6), leading to the
n-type doping of the material. However, there has been no report, except for our work, in

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Chapter 1
- 28 -
which organic radical molecules and polymers have been utilized as the electrode-active or
charge-storage component for a secondary battery.[123-125] Our idea is that the redox couple of
the nitroxide radical and of the phenoxyl radical are applicable for the cathode and anode
reaction of a secondary battery, respectively, as illustrated in Figure 1.4.9 (described later).
Figure 1.4.6 Redox couple of a nitroxide radical and a phenoxyl radical
Not only radical molecules, but also their oxidized (p-doped) and reduced (n-doped)
forms play important roles in battery electrode performance. For example, the oxidized form
of the TEMPO radical, that is, the oxoammonium cation salt, was isolated, which was robust
as well as the radical molecule under ambient conditions. Chemical stability of both the
radical and the doped forms is essential for durability of the charging and discharging
processes of the battery. Figure 1.4.7 shows the crystallographic structures and IR data of the
TEMPO derivative and its oxoammonium compound.[126] The latter was characterized by the
double band nature of N-O and almost planar C2O plane due to the sp2 character of the
nitrogen atom. However, the structural change between the radical and the oxoammonium
was very slight, which could be responsible for the rapid electron transfer reaction of the
radical molecule.
Figure 1.4.7 Structures of the nitroxide radical and oxoammonium cation of a TEMPO derivative
Electron-transfer rate constants (k0) for the nitroxide radicals and the phenoxyl radical in
solution were estimated to be on the order of 10-1 cm/s [127] (Table 1). This rapid

Page 35
Introduction
- 29 -
electron-transfer rate for the radical redoxes is the most important feature when compared to
the slow rates for the other organic redox reactions. For example, the electron-transfer rate
constants of 10-4 and 10-8 cm/s for the ascorbic acid oxidation and thional oxidation to form a
disulfide, respectively. The electron-transfer reactions of the radical molecules are rather
faster than that for the ferrocene, well-known as a standard molecule in electrochemical
reactivity, and are almost comparable to that for the copper ion.
The radical polymer electrode was prepared by coating the polymer on a current collector,
such as an ITO-PET film and glassy carbon substrate. In the radical polymer layer, an electron
is hopping or a charge is transferred (or propagated) via the redox reaction of the neighboring
radical moieties on the polymer (or the geared cycles of the radicals’ redoxes) (Figure. 8). The
redox process is accompanied by incorporation and transfer of a counter ion (here an anion) to
compensate the charge, which would be the rate-determing step of the charge propagation.
The diffusion coefficient (D) of the electron- or the charge-propagation in the radical polymer
layer was on the order of 10-9 cm2/s,[128] which was comparable to those of preciously
reported redox-active polymers, such as poly(vinylferrocene) (D = 10-9 cm2/s). The
amorphous, solvated, and slightly swollen structure of the radical polymer in the electrode
ensures a fast counter ion mobility during the charge-transfer process. These features afford a
high power-rate performance for the charging and discharging during battery applications of
the radical polymers.

Page 36
Chapter 1
- 30 -
Figure 1.4.8 Charge-propagation in the radical polymer layer
1.4.4 Performance of Totally-Organic Radical Polymer Battery
Radical polymers with different redox potentials can be employed as the cathode- and
anode-active materials in an all organic-based battery[129] (Figure 1.4.9). A representative
combination
is
the
poly(methacrylate)-combined
TEMPO,
poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl methacrylate) shown in the upper left section of
Figure. 11, as the cathode and the poly(galvinoxylstyrene) (the third listing in the lower
column of Figure. 12) as the anode. These two polymers were synthesized via the radical
polymerization of the corresponding non-radical precursor methacrylate and styrene
derivatives followed by chemical oxidation to generate the radical polymers. The radical
density of each polymer was >0.9 unpaired electrons per monomer unit. Solutions of the
radical polymers were coated as thin films on an ITO-PET substrate as the current collectors.
The coated radical polymers were suitably modified via a cross-linking reaction to impede
their dissolution into the electrolyte solution which causes self-discharging of the battery. A
micro-porous separator film containing the electrolyte solution, such as ethylenecarbonate
containing tetrabutylammonium chloride, was sandwiched between two radical polymer films
coated on the current collectors, in order to fabricate the all-organic battery consisting of
radical polymer electrodes, namely an all-organic “radical battery”.[130]
Figure 1.4.9 Totally-organic radical polymer battery (Li ion-free secondary battery)
Figure 1.4.10 is a picture of the paper-like and flexible, totally-organic radical battery.
The blue color in the charged state results from the galvinolate anion that dramatically

Page 37
Introduction
- 31 -
reverted to a light yellow color of the galvinoxyl radical in the discharged state. In a
see-through battery, the color change, accompanied by radical redox reactions, can be used as
an indicator of the charging level. The organic radical battery composed of the radical
polymer electrodes has several advantages:[125, 131] (1) a high charging and discharging
capacity (>100 mAh/g), ascribed to the stoichiometric redox of the radical moieties, (2) a
high-charging and -discharging rate performance resulting from the rapid electron-transfer
process of the radical species and from the amorphous state of the radical polymers, and (3) a
long cycle life, often exceeding 1000 cycles, derived from the chemical stability of the
radicals and from the amorphous electrode structure.
Figure 1.4.10 A flexible plastic battery totally composed of organic radical polymers
A series of radical polymers has been synthesized, and Figures 1.4.11 and 1.4.12 depict
the radical polymers previously reported by our groups.[123-134] A variety of polymer
backbones have been employed to bear the pendant radical groups, such as
poly(meth)acrylates, polystyrene, poly(vinyl ether)s, polyethers, and poly(norbornene)s. For
example, the backbones with a lower glass transition temperature or rubbery polymers often
produced a higher rate performance during the charging and discharging processes.
Figure 1.4.11 Nitroxide radical polymers based on various polymer backbones

Page 38
Chapter 1
- 32 -
We have extensively explored the n-type redox active radical polymers (Figure 1.4.12),
for example, introducing an electro-withdrawing group, such as a carbonyl and trifluorometyl
group, on the neighboring position of the nitroxide group in order to stabilize the n-type redox
pair and to tune the redox potential. The molecular design and synthesis based on Green
Chemistry are powerful strategies for developing organic functional materials including the
organic radical polymers.
Figure 1.4.12 n-Type radical polymers
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Page 44

Page 45
Chapter 2
Synthesis and Electrochemical Properties of TEMPO Substituted
Polyvinylether
2.1 Introduction
2.2 Synthesis of the TEMPO Substituted Polyvinylether
2.3 Electrochemical Properties of the TEMPO Substituted Polyvinylether
2.4 Cathode performance of the TEMPO Substituted Polyvinylether
2.5 Experimental Section
References

Page 46
Chapter 2
- 40 -
2.1 Introduction
Studies on high-performance charge-storage devices represented by lithium-ion batteries
have become of great interest in recent years.[1, 2] Many researchers have focused on
improvement of the charging-discharging rate performance by electrode surface
modifications,[3] and reduction of hazard risks and safety concerns [4] in the charge-storage
devices or batteries. The author proposed and reported secondary or rechargeable polymer
batteries which utilize radical polymers as an electrode-active material and the operation of
which is based on the redox property of the robust radicals [5-7]. The author has synthesized a
series of aliphatic polymers bearing the pendant robust radical groups (we called them
“radical polymers”) as electrode-active materials.[5-15] Rechargeable batteries composed of the
radical polymer-electrodes displayed advantages over previously reported organic
material-based batteries, such as batteries based on a doping process of polyacetylene[16] and a
redox reaction of thiol/disulfide derivatives[17]: (i) High charging and discharging capacity
(>100 mAh/g), ascribed to the stoichiometric redox of the radical moieties, (ii) High charging
and discharging rate performance caused by rapid electron-transfer process of the radicals,
and (iii) Long cycle life derived from the chemical stability of the radicals and from the
amorphous electrode structure.[9-13] These advantages also resulted from device fabrication
using organic electrolytes, such as the ethylenecarbonate-diethylenecarbonate solution
containing lithium perchlorate. On the other hand, any radical polymer which sufficiently
functions in aqueous electrolytes as an electrode has never been reported except in our
preliminary communication paper.[18]
A combination of a radical polymer and aqueous electrolyte is expected to improve the
charging-discharging rate performance. Aqueous electrolytes possess more than
10-times-higher equivalent electrical conductivity than organic electrolytes,[19] allowing a
very rapid charge diffusion even within polymer films. In addition, the combination of
aqueous electrolyte or the organic-solvent-free battery configuration could be expected to
reduce ignition and/or explosion risks of the rechargeable batteries.
Molecular design of the electrode-active radical polymer for working in aqueous
electrolytes would require a hydrophilicity or sufficient compatibility with water and selection
of robust radical species in aqueous electrolytes. The author preliminarily reported [18] a
hydrophilic radical polymer, poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl vinylether) (PTVE),
which is composed of a hydrophilic polyvinylether-backbone and a pendant robust
2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) group with redox capability even in aqueous
electrolytes. The PTVE also possessed a high formula-weight-based redox capacity per
weight of 135 mAh g-1, which was even higher than those of our previously reported
TEMPO-bearing radical polymers, a polymethacrylate-based one (PTMA) (111 mAh g-1)[14]

Page 47
Synthesis and Electrochemical Properties of TEMPO Substituted Polyvinylether
- 41 -
and a polynorbornene-based one (109 mAh g-1).[10, 12]
This chapter describes the hydrophilic radical polymer, PTVE, its high rate
charging-discharging performance as an electrode-active radical for rechargeable devices,
based on the combination of aqueous electrolytes, and a test battery fabricated with the PTVE
cathode, a zinc anode, and an aqueous electrolyte.
2.2 Synthesis of the TEMPO Substituted Polyvinylether
2.2.1 Monomer Synthesis
Although vinyl ethers are prepared by the reaction of acetylene with an alcohol, these
synthetic methods are not plausible due to their severe reaction conditions or toxicity of the
metal species used. The author thereby envisaged easier synthesis of vinyl ethers and focused
on the iridiumcatalyzed transformation of vinyl acetate into vinyl alcohols, which was
recently reported by Ishii. Their results indicated that the reaction was possible for an alcohol
bearing a TEMPO radical moiety. The method for synthesizing the vinyl ether monomer
bearing a TEMPO radical and the corresponding polymer are shown in Scheme 2.1. First, the
monomer was synthesized by reacting vinyl acetate and TEMPO–OH in the presence of 2
mol-% of [IrCl(cod)]2.
2.2.2 Polymer Synthesis
PTVE with a molecular weight of Mn=78 000 (Mw/Mn =1.2) was prepared by cationic
polymerization of 2,2,6,6-tetrametylpiperidne-N-oxyl-4-vinyl ether in dichloromethane using
trifluoroborane–diethylether as the initiator. The obtained polymer was characterized by
elemental analysis and 1H- and 13C-NMR spectroscopes, supporting the fact that the cationic
polymerization proceeded without any side reactions. The polymer was soluble in acetonitrile,
but swollen and not soluble in water.
Scheme 2.1 Synthesis procedure of PTVE.
2.2.3 Unpaired Electron Concentration
The TEMPO radical moiety of PTVE was characterized with ESR spectroscopy and
SQUID magnetic measurement. g-Value (2.0067) in the ESR signal (inset of Figure 2.1)
agreed with that of TEMPO (2.0056 [20]). Broadening of the ESR spectrum was explained by
an intrachain dipole-dipole interaction due to the close proximity of the polymer-bound

Page 48
Chapter 2
- 42 -
radical moieties. The unpaired electron concentration of PTVE was determined by SQUID
using Curie-Weiss plots (Figure 2.1). The linear relation was ascribed to a typical
paramagneric behavior of the unpaired electrons of PTVE, and its slope gave the unpaired
electron or radical concentration of the PTVE sample, in the example of Figure 2.1, of 0.97
per monomer unit of PTVE. A maximum effective charging-discharging capacity per weight
of 131 mAh g-1 was calculated using formula-weight-based charging-discharging capacity 135
mAh g-1× 0.97. The unpaired electron concentration almost maintained over three months
under ambient conditions.
Figure 2.1 Curie-Weiss plots of 1/magnetic susceptibility (χg) vs. temperature (K) for the powder
sample of PTVE. Inset: ESR spectrum at room temperature.
2.2.4 Thermal Properties and Hydrophilic Properties
Thermal analysis of the PTVE powder sample revealed that PTVE itself was stable up to
around 250°C: The 10%-decomposition temperature was 276°C (Figure 2.2). The unpaired
electron concentration in PTVE was maintained up to 150°C. The TEMPO radical moiety in
PTVE was robust in these applications. The glass transition temperature (Tg) of PTVE was
Figure 2.2 Relative concentration of unpaired electrons (●) and relative weight (—) of the powder
sample of PTVE. Inset: DSC thermogram.

Page 49
Synthesis and Electrochemical Properties of TEMPO Substituted Polyvinylether
- 43 -
124°C, which was higher than that of other polyvinylethers such as poly(tert-butoxyethylene)
(Tg = 88°C[21]) and poly(cyclohexyloxyethylene) (81°C[21]). The higher Tg could be derived
from the sterically bulky TEMPO moiety.
The hydrophilic property of the PTVE film was examined by contact angle measurement
of a water droplet on the surface of PTVE film (The surface formed by spin-coating was
smooth with a roughness of ± 4 nm on an AFM image). The contact angle was 65‒71°, which
was significantly smaller than 82‒89° for the surface of the lipophilic polymethacylate-based
TEMPO Polymer (PTMA), and supported the hydrophilicity of the PTVE polymer. The
volume swell ratio of the PTVE film (thickness of 1.1 μm) was estimated by microscopic
analysis of the polymer volume before and after swelling in water. The degree of swelling
under equilibrated conditions was ca. 1.2 (v/v), which indicated that the polymer had a
sufficient water absorbability for functioning as an electrode-active material in aqueous
electrolytes.
2.3 Electrochemical Properties of the TEMPO Substituted Polyvinylether
2.3.1 Redox Properties
The PTVE film with a thickness of 60 nm displayed a chemically reversible redox wave
at 0.73 V (vs. Ag/AgCl) in 0.1 M aqueous NaCl at pH 6.8 (Figure 2.3). The redox wave
showed a narrow peak-to-peak separation (∆E = 16 mV) for the film with a thickness of <35
nm, indicating electrochemically reversible and very fast electron transfer within the polymer
film. This arose both from the fast electrode kinetics of PTVE and the rapid diffusion of
counter ions in aqueous electrolytes, leading to a Nernstian adsorbate-like behavior despite
the substantial thickness of the polymer film. The anodic or oxidation peak was sharper than
the cathodic or reduction peak in Figure 2.3, although the oxidation and reduction capacities
or the peak areas almost coincided with each other. This redox wave shape was similar to that
of the polyvinylferrocene redox in aqueous electrolytes. Jureviciute et al.[22] discussed that the
sharp oxidation peak was ascribed to a rapid incorporation of counter ions and that the
broadened reduction peak would be caused by a slow releasing of hydrated counter ions.
Scheme 2.2 Redox couple of PTVE.

Page 50
Chapter 2
- 44 -
In an aqueous NaCl solution with a pH of 1–8 or under a neutral and acidic condition, the
PTVE film, showed chemically reversible redox ability and gave almost quantitative redox
capacity (inset in Figure 2.3). On the other hand, the redox wave of PTVE was attenuated
with a voltage sweep in the aqueous solution at pH >9, probably because the oxoammonium
cation, generated by oxidation of the nitroxide radical, suffered a nucleophilic attack by
hydroxide ion and was converted to an electrochemically inert species.[23, 24]
Figure 2.3 Cyclic voltammogram of the PTVE film with a thickness of 60 nm coated on a glassy
carbon substrate in 0.1 M aqueous NaCl. Inset: Redox capacity relative to pH.
2.3.2 Thickness Dependency
The redox capacity of PTVE was proportional to the film thickness and reached 45 mC
cm-2 for a film with a thickness of 1 μm (Figure 2.4), even in the absence of conductive
additives which are frequently employed in battery electrodes. This result means that the
PTVE polymer was homogeneously solvated with the aqueous electrolyte phase to
Figure 2.4 Redox capacity per area for the PTVE film with a thickness of 35 nm–1 μm. The solid line
represents the calculated redox capacity for the coating amount.

Page 51
Synthesis and Electrochemical Properties of TEMPO Substituted Polyvinylether
- 45 -
compensate for the charge and that almost all of the TEMPO moiety of the PTVE functioned
as the redox site. These results also suggested that the polymer film fabricated by a
solution-based, e.g., spin-coating, process did not involve any structural defects to decrease
the capacity and to prevent the charge transfer within the polymer film.
2.3.3 Charge Propagation Analysis
The effects of electrolyte species on the redox property, especially on the charge
propagation within the PTVE film, were studied by impedance analysis for a half-cell of the
PTVE electrode, using 0.1 M aqueous NaCl solution, aqueous (C4H9)4NCl solution, and
(C4H9)4NCl ethylene carbonate/diethylene carbonate (50/50 v/v) (EC/DEC) solution.
Impedance plots of the PTVE electrode showed three regions in the diagram of the imaginary
part of the impedance vs. the real part of the impedance (Figure 2.5): a kinetic control region,
a diffusional control region, and a charge saturation region. At high frequencies of ω >5 Hz,
the semicircular plots reflected the average rate of injection and removal of electrons and
counter ions into the polymer film. At intermediate frequencies of 5> ω >0.5 Hz, the
impedance plots were linear with unity slope. At very low frequencies of ω <0.3 Hz , the
impedance was capacitive reflecting charge saturation limited by the finite polymer thickness.
In the kinetic control region, semicircular plots gave solution resistance (Rs) and charge
transfer resistance (Rc) of the half-cells of the PTVE electrode, given in Table 2.1. The PTVE
half-cells using the aqueous electrolytes showed very low solution resistance originating from
the aqueous electrolytes possessing 10-times-higher equivalent electrical conductivity than
those of an electrolyte using organic solvents such as EC/DEC. The half-cells using the
aqueous electrolytes also showed lower charge transfer resistance and higher charge diffusion
Figure 2.5 Impedance spectra for the charge propagation condition of the PTVE film in 0.1 M NaCl
aq. (●), TBACl aq. (□), and TBACl EC/DEC solution (○) using the half-cell.

Page 52
Chapter 2
- 46 -
constants within the polymer film than those for a half-cell using the organic EC/DEC
electrolyte. These results denote that electrolyte species affected not only the solution
resistance but also the charge propagation within the polymer film. The combination of the
hydrophilic PTVE and aqueous electrolytes could result in fast charge propagations or counter
ions diffusion within the radical polymer film, which would lead to a rapid
charging-discharging process of the PTVE electrode in aqueous electrolytes.
Table 2.1 Solution resistance (RS), Charge transfer resistance (RC) and diffusion constant (D) for the
charge propagation in the PTVE film
2.4 Cathode performance of the TEMPO Substituted Polyvinylether
2.4.1 Charging-discharging Performance
Charging-discharging curves for the half-cell composed of the PTVE film as the working
electrode in 0.1 M NaCl aq. exhibited a plateau voltage at 0.71‒0.75 V (vs. Ag/AgCl) (inset in
Figure 2.6), which agreed with the redox potential of the PTVE film (0.73 V) shown in Figure
2.3. The charging-discharging capacities almost coincided at ca. 131 mAh g-1 and agreed with
the calculated capacity obtained in Figure 2.4 (2.8 mC cm-2 × 60 nm thickness), even under
very rapid charging-discharging at the C-rate of 60 C. (Most conventional batteries function in
charging or discharging at 1C that takes 1h.)
Figure 2.6 Columbic efficiency (●) and discharging capacity (○) for the half-cell composed of the
PTVE film on the charging–discharging cycle number at the charging–discharging rate of 60 C (45 μA
cm-2). Inset: Charging-discharging curve of the PTVE film.

Page 53
Synthesis and Electrochemical Properties of TEMPO Substituted Polyvinylether
- 47 -
The cycle performance of the charging-discharging at cutoff voltages of 0.6‒1.0 V and
the C-rate of 60 C is shown also in Figure 2.6. Even after 1000 charging-discharging cycles,
the coulombic efficiency (discharging capacity over the charging capacity) was maintained at
almost 100%, indicating that the charged species, the oxoammonium form of PTVE,
stoichiometrically contributed to the following discharging process. However, the discharging
capacity decreased to ca. 75% of the initial value after 1000 cycles. In the one experiment
using the PTVE sample with a higher molecular weight of Mn=135 000, the discharging
capacity of the PTVE electrode was maintained at 92% of the initial capacity after 1000
cycles. These results suggested that the capacity decrease was derived from partial elution out
of the PTVE polymer into the electrolyte, which could be impeded through slight crosslinking
of the polymer.
2.4.2 Charging-discharging Rate Performance
To examine the charging rate performance, the PTVE half-cell using 0.1 M NaCl aq. was
charged at a 60‒1200 C-rate and then discharged at 60 C (Figure 2.7 and inset). Discharging
capacity was almost maintained even with the tremendously rapid charging at 1200 C,
indicating that the PTVE cathode could be fully charged even in 3 seconds. The fully charged
PTVE half-cell was discharged at a 60‒1200 C-rate to examine the discharging rate
performance. The discharging capacity gradually decreased with the C-rate (Figure 2.7).
These results suggest that the charging of the PTVE electrode is faster than the discharging.
The fast charging or oxidation of the nitroxide radical of PTVE could be attributed to a rapid
compensation of counter ions into the hydrophilic PTVE film, and the relatively slow
discharging or regeneration of the radical would be caused by a slow releasing of the hydrated
counter ions from the PTVE film. This charging-discharging behavior does not conflict with
the asymmetric redox wave of PTVE as had been described in Figure 2.3.
2.4.3 Influence on the Electrolyte for Charging-discharging Rate Performance
The effects of the electrolyte species on the charging and discharging rates of the PTVE
electrode were studied on the half-cell using the electrolytes of 0.1 M NaCl aq., (C4H9)4NCl
aq. and (C4H9)4NCl EC/DEC. Under the charging and discharging rate at 60 C, the charging
and discharging capacities were coincided with each other almost at the value of 131 mAh g-1
calculated using the film amount of PTVE for the three cells using different electrolytes. In
comparing the charging carves, the charging capacity for the cell using the (C4H9)4NCl aq.
was maintained even at the high C-rate.

Page 54
Chapter 2
- 48 -
Figure 2.7 Charging-rate performance of the half-cell of the PTVE film using the electrolyte of 0.1 M
NaCl aq. (●), (C4H9)4NCl aq. (□), and (C4H9)4NCl EC/DEC (○). Inset: Charging-discharging curves for
the cell using the 0.1 M NaCl aq..
On the other hand, the charging capacity for the cell using the organic (C4H9)4NCl
EC/DEC solution significantly decreased at the high C-rate of >240 C and to almost half of
the initial capacity at 1200 C (Figure 2.7). For the discharging rate carves, the discharging
capacity for the cell using the (C4H9)4NCl aq. slightly decreased with increasing C-rate;
however, that for the cell using, the organic (C4H9)4NCl EC/DEC solution was reduced to
30% of the initial capacity at 1200 C (Figure 2.8). The combination of aqueous electrolytes
and the hydrophilic radical polymer PTVE electrode was very effective in allowing high rates
in the charging-discharging processes.
Figure 2.8 Discharging-rate performance of the half-cell of the PTVE film using 0.1 M NaCl aq. (●),
(C4H9)4NCl aq. (□), and (C4H9)4NCl EC/DEC (○).
Inset: Discharging curves at discharging-rate of 600 C.

Page 55
Synthesis and Electrochemical Properties of TEMPO Substituted Polyvinylether
- 49 -
In summary, a polyvinylether-based TEMPO radical polymer, PTVE, was synthesized
and characterized as a hydrophilic and electrode-active polymer. The PTVE film even with a
thickness of 1 μm coated on a current collector and equilibrated with aqueous NaCl solutions
of pH 1‒8 showed reversible redox capacity in agreement with that calculated based on the
film thickness, concluding that the PTVE film was defect-free for the one-electron redox of
the TEMPO moiety and was homogeneously solvated with the aqueous electrolyte. The
half-cell composed of the PTVE electrode showed a very rapid charging-discharging
performance based on virtue of the combination of the hydrophilic radical polymer and the
aqueous electrolyte possessing a high electrical conductivity.
2.5 Experimental Section
Martial
Monomer Synthesis
2,2,6,6-Tetramethylpiperidinyloxy-4-yl vinylether was prepared as follows: To a mixture
of TEMPO-OH (2.5g), Na2CO3 (1.5g) and [IrCl(cod)]2 (0.2 g) in 25 ml of dry toluene, vinyl
acetate (2.7 ml) was added. The mixture was stirred at 90°C for 6 h. The reaction mixture was
concentrated with a rotary evaporator, and then added to 50 ml of hexane and stirred at for
10min. The mixture was passed through a Celite pad to remove any solid residue. The pad
was washed with hexane. The combined filtrate was purified by flash chromatography on
silica gel (hexane/ethyl acetate = 5:1) to afford the corresponding monomer as a red solid.
Polymer Synthesis
Poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl vinylether) (PTVE) wa prepared as follows[25,
26]: To a solution of vinylether monomer (1.0g) in 10 ml of dry CH2Cl2, BF3-Et2O (12.8 ml)
was added at -78°C. The mixture was left to rest at -25°C for 20 h. After the polymerization
reaction, the resulting mixture changed to viscous reddish gel, which was washed with
methanol to remove the initiator. The residue was dried under reduced pressure to afford
PTVE as a red slid (64% yield)
The molecular weight of the polymer was Mn=78 000 with a dispersity of Mw/Mn =1.2.
Elemental analysis of PTVE: C, 65.9; H, 9.9; and N, 6.8; Calcd. for C11H20NO2: requires C,
66.6; H, 10.1;and N, 7.1. The PTVE was chemically reduced with phenylhydrazine, and
characterized by NMR spectroscopy. δH (500 MHz; CD3CN; Me4Si) 3.85 (1 H, m, piperidine
CH), 3.68 (1 H, br s, OCHCH2), 1.93 (2 H, m, piperidine CH2), 1.79 (2 H, m, piperidine CH2),
1.32 (2 H, br s, OCHCH2), 1.11 (6 H, s, 2 × CH3), 1.10 (6 H, s, 2 × CH3); δC(500 MHz;
CD3CN; Me4Si) 20.7, 33.1, 48.9, 59.6, 63.1, 74.8, 75.6.

Page 56
Chapter 2
- 50 -
Determination of the Radical Content
PTVE was characterized by the g-value (2.0067) of the ESR signal, which was in
agreement with that of TEMPO. The radical concentrations were determined, assuming that
the polymer was paramagnetic at room temperature, by comparing the integrated ESR
intensity with that of the TEMPO powder as the standard. The radical concentration was also
determined by means of SQUID measurements using the Curie-Weiss plot. The two
independently determined values agreed well each other.
Electrode Preparation and Electrochemical Measurements
The acetonitrile solutions of PTVE (10‒50 g/L) were spin-coated on a current collector
such as a glassy carbon substrate, followed by drying at 80˚C for 24 hr under vacuum, to yield
the PTVE film with a thickness of 35 nm‒1 μm, respectively.
The electrochemical measurements were performed using a conventional three-electrode
cell under standard ambient condition. A normal potentiostat system (BAS Inc. ALS660B)
was used for the cyclic voltammetry, chronopotentiometry and other electrochemical
measurements. A coiled platinum wire and Ag/AgCl were used as the counter and reference
electrode. The cyclic voltammogram was measured in a 0.1 M NaCl aq. and its pH were
controlled adding HCl and NaOH.
The chronopotentiometry were measured in 0.1 M NaCl aq., 0.1 M (C4H9)4NCl aq. and
0.1 M (C4H9)4NCl ethylene carbonate/diethylene carbonate (50/50 v/v) electrolyte. (1) Cycle
performance test: the PTVE half cell was charged and discharged at 60 C repeatedly until
1000 cycles. (2) Charging rate performance test: the PTVE half cell was charged at the
60‒1200 C-rate, and its discharging capacity was measured at 60 C. (3) Discharging rate
performance test: the PTVE half cell, fully charged at 60 C, was discharged at a 60‒1200
C-rate, and the discharging capacities were measured.
The impedance spectrum ware measured in 0.1 M NaCl aq., 0.1 M (C4H9)4NCl aq. and
0.1 M (C4H9)4NCl ethylene carbonate/diethylene carbonate (50/50 v/v) electrolyte. The range
of frequencies applied was 0.1 to 2500 Hz
Other Measurements
The 1H- and 13C NMR spectra were recorded using a JEOL Lambda 500 or Bruker
AVANCE 600 spectrometer, and Gel permeation chromate graphy was performed with DMF
using a Tosoh HLC-8220 instrument. Electron spin resonance (ESR) spectra were obtained
using a JEOL JES-TE200ESR spectrometer with 100 kHz field modulation. The
magnetization and magnetic susceptibility of the powder polymer sample were measured by
Quantum Design MPMS-7SQUID (superconducting quantum interference device)
magnetometer. The magnetic susceptibility was measured from 10 to 300 K in a 1.0 T field.

Page 57
Synthesis and Electrochemical Properties of TEMPO Substituted Polyvinylether
- 51 -
The thermal analyses were performed with a Seiko DSC220C and a TG/DTA 220 thermal
analyzer at a heating rate of 10°C/min under helium.
References
[1] G. Pistoia, "Batteries For Portable Devices ", Elsevier Amsterdam, 2005.
[2] B. Scrosati, W. A. V. Schalkwijk, "Advances in Lithium-Ion Batteries", Plenum
Publishers, 2002.
[3] L. J. Fu, H. Liu, C. Li, Y. P. Wu, E. Rahm, R. Holze, H. Q. Wu, Solid State Sci. 2006, 8,
113.
[4] M. Galinski, A. Lewandowski, I. Stepniak, Electrochimica Acta 2006, 51, 5567.
[5] H. Nishide, K. Oyaizu, Science 2008, 319, 737.
[6] K. Oyaizu, H. Nishide, Adv. Mater. 2009.
[7] H. Nishide, K. Koshika, K. Oyaizu, Pure Appl. Chem. 2009.
[8] H. Nishide, T. Suga, Electrochem. Soc. Interface 2005, 14, 32.
[9] T. Suga, H. Ohshiro, S. Sugita, K. Oyaizu, H. Nishide, Adv. Mater. 2009, 21, 1627.
[10] T. Suga, H. Konishi, H. Nishide, Chem. Commun. 2007, 1730.
[11] T. Suga, Y. J. Pu, S. Kasatori, H. Nishide, Macromol. 2007, 40, 3167.
[12] K. Oyaizu, Y. Ando, H. Konishi, H. Nishide, J. Am. Chem. Soc. 2008, 130, 14459.
[13] K. Oyaizu, T. Suga, K. Yoshimura, H. Nishide, Macromol. 2008, 41, 6646.
[14] H. Nishide, S. Iwasa, Y. J. Pu, T. Suga, K. Nakahara, M. Satoh, Electrochim. Acta 2004,
827.
[15] K. Nakahara, S. Iwasa, M. Satoh, Y. Morioka, J. Iriyama, M. Suguro, E. Hasegawa,
Chem. Phys. Lett. 2002, 359, 351.
[16] D. Macinnes, M. A. Druy, P. J. Nigrey, D. P. Nairns, A. G. Macdiarmid, A. J. Heeger,
Journal of the Chemical Society-Chemical Communications 1981, 317.
[17] N. Oyama, T. Tatsuma, T. Sato, T. Sotomura, Nature 1995, 374, 196.
[18] K. Koshika, N. Sano, K. Oyaizu, H. Nishide, Chem. Commun. 2009, 836.
[19] D. R. Lide, in Handbook of Chemistry and Physics, 72nd edition, CRC Press, Boston,
1991, p. 96.
[20] M. Weng, M. H. Zhang, T. Shen, Dyes and Pigments 1998, 36, 93.
[21] J. Brandrup, E. H. Immergut, in Polymer Handbook, Third Eddition edition,
Wiley-Interscience Publication, Weinheim, 1989, p. 220.
[22] I. Jureviciute, S. Bruckenstein, A. R. Hillman, J. Electroanal. Chem. 2000, 488, 73.
[23] J. R. Fish, S. G. Swarts, M. D. Sevilla, T. Malinski, J. Phys. Chem. 1988, 92, 3745.
[24] Y. Kato, Y. Shimizu, Y. J. Lin, K. Unoura, H. Utsumi, T. Ogata, Electrochimica Acta
1995, 40, 2799.
[25] M. Suguro, S. Iwasa, Y. Kusachi, Y. Morioka, K. Nakahara, Macromol. Rapid Commun.

Page 58
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2007, 28, 1929.
[26] M. Suguro, S. Iwasa, K. Nakahara, Macromol. Rapid Commun. 2008, 29, 1635.

Page 59
Chapter 3
Redox Properties of TEMPO Substituted Polyvinylether on Aqueous
Electrolyte Conditions and its Battery performance of Test-Cell
Fabricated with Zinc Anode
3.1 Introduction
3.2 Redox Properties on pH
3.3 Redox Properties on Salt Concentration
3.4 Redox Properties on Variety of Salts
3.5 Battery performance of the Test-Cell Fabricated with Zinc Anode
3.6 Experimental Section
References

Page 60
Chapter 3
- 54 -
3.1 Introduction
Some of nitroxide radical molecules such as 2,2,6,6-tetramethylpiperidine-1-oxyl
(TEMPO) are robust and known to show reversible redox ability in organic and aqueous
solutions,[1] and they have been often studied as a redox mediator in sensors[2] and catalysts[3].
We have synthesized a series of aliphatic polymers bearing the pendant nitroxide radical
groups and utilized them as an electrode-active or the charge-storage material applicable in
secondary or rechargeable batteries.[4-11] The radical polymer battery fabricated with the
nitroxide radical polymer as the cathode showed the following features; high
charging-discharging capacity ascribed to the stoichiometric redox of the nitroxide radical,
high charging-discharging rate resulting from the rapid electron-transfer process of the
nitroxide radical, and long cycle-life derived from the chemical stability of the nitroxide
radical.
Recently,
we
designed
a
hydrophilic
radical
polymer,
poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl vinylether) (PTVE), which is composed of a
hydrophilic
polyvinylether-backbone
and
a
pendant
robust
2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) group with redox capability even in aqueous
electrolytes. The PTVE sufficiently functioned even in an aqueous electrolyte, and reported
the following electrode performance [12, 13]: (i) High charging and discharging capacity of 131
mAh g-1 ascribed to the stoichiometric redox of the radical moieties, (ii) Long cycle life,
often exceeding 1000 cycles, derived from the chemical stability of the radicals and from the
amorphous electrode structure, and (iii) High charging-discharging rate performance (1200 C)
resulting from the rapid electron-transfer process of the radical moiety and the high equivalent
electrical conductivity of the aqueous electrolyte on the order of 10-2–10-3 m2 S mol-1, which
is 10-times higher than that of organic electrolytes.[14] (The rate of 1 C is defined as the
current density at which the charging or discharging of the cell takes 1h. Most conventional
batteries function during the charging or discharging at 1–2 C.) These results were obtained
under the neutral condition of 0.1 M NaCl aq. Generally, redox active polymers such as
polyvinylferrocene and polyviologen were known to change their redox properties by their
electrolyte conditions such as pH, salt concentration, and salt species.
However the affection of electrolyte condition for redox properties of radical polymers
has never been reported. Research for the conditions in which radical polymer works with a
high performance, was very important for test full-cell fabrication due to the combination for
electrolytes and counter electrode. In this chapter, we report influence for redox properties of
PTVE film on electrolyte conditions, such as pH, salt concentration, and salt species. Based
on this information, the test-full cell was fabricated with PTVE cathode, zinc anode and
ZnCl2-NH4Cl aq.. The test-cell performance is also reported.

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Redox Properties of TEMPO Substituted Polyvinylether on Electrolytes
and its Battery performance of the Test-Cell with Zinc Anode
- 55 -
3.2 Redox Properties on pH
The PTVE film with a thickness of 60 nm displayed a chemically reversible redox wave
at 0.73 V (vs. Ag/AgCl) in 0.1 M aqueous NaCl at pH 6.8. The redox wave showed a narrow
peak-to-peak separation (∆E = 16 mV) for the layer with a thickness of <35 nm, indicating
electrochemically reversible and very fast electron transfer within the polymer layer. This
arose both from the fast electrode kinetics of PTVE and the rapid diffusion of counter ions in
aqueous electrolytes, leading to a Nernstian adsorbate-like behavior despite the substantial
thickness of the polymer layer.
Scheme 3.1 Redox couple of PTVE.
Effect of pH conditions on redox property of PTVE was examined. In an aqueous NaCl
solution with a pH of 1–8 or under a neutral and acidic condition, the PTVE layer showed
chemically reversible redox ability and gave almost quantitative redox capacity (inset in
Figure 3.1. (a)). On the other hand, the redox wave of PTVE was attenuated with a voltage
sweep in the aqueous solution at pH >9, probably because the oxoammonium cation,
generated by oxidation of the nitroxide radical, suffered a nucleophilic attack by hydroxide
ion and was converted to an electrochemically inert species.[15, 16]
Figure 3.1 Relative redox capacities of PTVE film on several pH conditions. Inset: Cyclic
voltammograms of PTVE film (a) pH 1 and (b) pH 11.

Page 62
Chapter 3
- 56 -
3.3 Redox Properties on Salt Concentration
The effects of electrolyte salt concentration on the redox property, especially on the redox
potential, was studied by cyclic voltammograms for a half-cell of the PTVE electrode, using
NaCl aq., NaPF6 aq., and Na2SO4 aq.. In the aqueous NaCl solution with concentration of
0.001―0.5 M, PTVE showed chemically reversible redox ability and quantitative redox
capacity. The redox potential of PTVE film in NaCl aq. was decreased in proportion of salt
concentration with a slope of 59 mV. The redox potential in NaPF6 was also decreased in
proportion with a slope of 59 mV (Figure 3.2.(a)). These results mean that the counter anion
was contained in a redox equation of PTVE and PTVE+, as follows.
PTVE
[PTVE X]
+ Xn-
+ ne-
][log
59
][]
[
]
[
log
0
0
-
-
-
=
+
=
n
a
n
a
a
a
X
n
mV
EE
X
PTVE
X
PTVE
nF
RT
EE
On the other hand, the redox potential in Na2SO4 was decreased in proportion with a slope of
28 mV, which was almost correspond to 59/2 mV derived from the dianion of SO4
2-.This
result supported above prediction, and indicated the redox properties were influenced by the
salt species strongly.
Figure 3.2 Redox potentials dependency on electrolyte salt concentration (a) NaCl and NaPF6, (b)
Na2SO4.

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Redox Properties of TEMPO Substituted Polyvinylether on Electrolytes
and its Battery performance of the Test-Cell with Zinc Anode
- 57 -
3.4 Redox Properties on Variety of Salts
3.4.1 Cyclic Voltammograms
The effects of electrolyte species on the redox property, especially on the charge
propagation within the PTVE film, were studied by cyclic voltammometry, and impedance
analysis for a half-cell of the PTVE electrode, using 0.1 M NaCl aq., NaBF4 aq., and NaPF6
aq.. The PTVE film showed redox waves with different shapes in aqueous electrolytes. In
NaCl aq., the PTVE displayed reversible redox wave at 0.72 V vs. Ag/AgCl with narrow peak
separation of 27 mV. On the other hand, in NaBF4 aq., and NaPF6 aq., the PTVE displayed
reversible redox wave at 0.65 and 0.54 V vs. Ag/AgCl with wider peak separations of 65 and
165 mV, respectively.
Figure 3.3 Cyclic voltammograms of PTVE film in (a) NaCl aq., (b) NaBF4 aq., and (c) NaPF6 aq.
These redox capacities calculated with anion spices indicated that the charge propagations
influence on anion spices. The from cyclic voltammograms were agreed with 131 mAh g-1.
The difference peak separations diffusion of chloride anion within the polymer could be the
fastest among them due to its small size. However, TEMPO in 0.1 M NaCl aq., NaBF4 aq.,
and NaPF6 aq. showed same redox waves (Figure 3.4). This difference indicated the different
redox waves of PTVE derived from a instruction between polymer and anion species.
Figure 3.4 Cyclic voltammograms of TEMPO in NaCl aq., NaBF4 aq., and NaPF6 aq..

Page 64
Chapter 3
- 58 -
3.4.2 Charging-Discharging Rate Performance
Discharging curves of PTVE film in NaCl aq., NaBF4 aq., and NaPF6 aq. gave plateau
voltages at 0.67–0.72, 0.62–0.65, and 0.55–0.51, respectively (Figure 3.5. (a), (b) and (c)),
which were almost coincided with redox potentials of cyclic voltammograms (Figure 3.3.).
Figure 3.5 Charging-discharging rate performance of PTVE film in aqueous electrolytes: (a) NaCl aq.,
(b) NaBF4 aq. and (c) NaPF6 aq..
The charging-discharging rate performance was summarized in Figure 3.6. The PTVE
was charged and discharged at a 20–1200 C-rate. In comparing the discharging carves, the
discharging capacity for the cell using the NaCl aq. was maintained even at the high C-rate.
On the other hand, the discharging capacity for the cells using the NaBF4 aq., and NaPF6 aq.
significantly decreased at the high C-rate of >50 C and to almost half of the initial capacity at
120 C. This result supported above estimation that interaction between the polymer and anion
species influence on charge propagation within the polymer. The combination of aqueous
NaCl solution and the hydrophilic radical polymer PTVE electrode was very effective in
allowing high rates in the charging-discharging processes.
Figure 3.6 Comparing rate performance in 0.1 M NaCl aq. (●), NaBF4 aq. (○), and NaPF6 aq. (■) using
the half-cell.

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Redox Properties of TEMPO Substituted Polyvinylether on Electrolytes
and its Battery performance of the Test-Cell with Zinc Anode
- 59 -
3.4.3 Charge Propagation Analysis
Impedance plots of the PTVE electrode showed three regions in the diagram of the
imaginary part of the impedance vs. the real part of the impedance (Figure 3.6): a kinetic
control region, a diffusional control region, and a charge saturation region. At high
frequencies of ω >5 Hz, the semicircular plots reflected the average rate of injection and
removal of electrons and counter ions into the polymer layer. At intermediate frequencies of
5> ω >0.5 Hz, the impedance plots were linear with unity slope. At very low frequencies
of ω <0.3 Hz , the impedance was capacitive reflecting charge saturation limited by the finite
polymer thickness. In the kinetic control region, semicircular plots gave solution resistance
(RS) and charge transfer resistance (RC) of the half-cells of the PTVE electrode, given in Table
3.1. The PTVE half-cells using the aqueous electrolytes showed very low solution resistance
originating from the aqueous electrolytes possessing 10-times-higher equivalent electrical
conductivity than those of an electrolyte using organic solvents such as EC/DEC. The
half-cells using the aqueous electrolytes also showed lower charge transfer resistance and
higher charge diffusion constants within the polymer layer than those for a half-cell using the
organic EC/DEC electrolyte. These results denote that electrolyte species affected not only the
solution resistance but also the charge propagation within the polymer layer. The combination
of the hydrophilic PTVE and aqueous electrolytes with especially chloride ion could result in
fast charge propagations or counter ions diffusion within the radical polymer layer, which
would lead to a rapid charging-discharging process of the PTVE electrode in aqueous
electrolytes.
Figure 3.6 Impedance spectra for the charge propagation condition of the PTVE layer in 0.1 M NaCl
aq. (●), NaBF4 aq. (○), and NaPF6 aq. (■) using the half-cell.

Page 66
Chapter 3
- 60 -
Table 3.1 Impedance data of PTVE film in aqueous electrolytes
3.4.4 Redox Capacity on Film Thickness
The redox capacity of PTVE in NaCl aq. was proportional to the film thickness and
reached 45 mC cm-2 for a film with a thickness of 1 μm (Figure 3.7), even in the absence of
conductive additives which are frequently employed in battery electrodes. This result means
that the PTVE polymer was homogeneously solvated with the aqueous electrolyte phase to
compensate for the charge and that almost all of the TEMPO moiety of the PTVE functioned
as the redox site. On the other hand, the redox capacity of PTVE in NaPF6 was quantitative
proportional to the film thickness until 150 nm. Then the capacities with film thickness of 240,
430, and 590 were almost same amount. This result indicated that the diffusion of PF6 ion
within the polymer was slower than that of Cl-. Quantitative redox capacity would be obtained
by slower sweep of potential (less than 1 mV s-1).
Figure 3.7 Redox capacities of PTVE film on film thickness in 0.1 M NaCl aq. (●). and NaPF6 aq.
(■).

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Redox Properties of TEMPO Substituted Polyvinylether on Electrolytes
and its Battery performance of the Test-Cell with Zinc Anode
- 61 -
3.5 Battery performance of the Test-Cell Fabricated with Zinc Anode
A test full-cell was fabricated using the PTVE cathode and a zinc anode in the aqueous
solution of 0.1 M ZnCl2 and 0.1M NH4Cl. The charging-discharging curves for the fabricated
cell displayed a plateau voltage at 1.73 V (vs. Zn/Zn2+) with the capacity of 124 mAh g-1
(Figure 3.8). The charging capacity over the 131 mAh g-1 indicated that the charged species,
the oxoammonium form of PTVE, were partially reduced by zinc in electrolyte (which could
be impeded through separator). The cycle performance of the charging-discharging at the
cut-off voltages of 1.0‒2.0 V and C-rate of 60 C is shown in the inset of Figure 7. The
columbic efficiency is maintained at almost 80% even after 500 charging-discharging cycles.
The discharging capacity gradually decreases to ca. 65% of the initial after 500 cycles. These
results supported the potential of the aqueous electrolyte-based organic radical polymer
battery.
Figure 3.8 Charging–discharging curve of the test cell fabricated with PTVE cathode, zinc anode,
aqueous solution of 0.1 M ZnCl2 and 0.1 M NH4Cl.Inset: coulombic efficiency (●) and discharging
capacity (○) on the cycle number
In summary, Redox ability of PTVE was stable in acidic and neutral condition with pH
1‒8. Salt concentrations effected redox potential, indicating that concentration of counter ions
were contained in redox process equation as an important factor. Selection of counter ion
species effected charging-discharging properties such as, charging-discharging rate
performance, charge transfer resistance, and capacity on film thickness. Among the three ions,
chloride ion was the most effective for demonstrating a high charging-discharging
performance, such as high redox potential, rapid charging and high capacity. Based on this
data, the author fabricated semi-organic model radical battery composed of the PTVE cathode
and a zinc anode in the aqueous solution of 0.1 M ZnCl2 and 0.1M NH4Cl. The test full-cell
demonstrated quantitative charging-discharging property, supporting its practical expectation.

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Chapter 3
- 62 -
3.6 Experimental Part
Martial
PTVE was prepared as follows: 2,2,6,6-tetrametylpiperidne-N-oxyl-4-vinyl ether) was
prepared by using coupling reaction of 4-hydroxy-TEMPO and vinyl acetate at 90°C. Then
the PTVE monomer was polymerized by cationic polymerization in dichloromethane with
trifluoroborane–diethylether as the initiator at -25°C.
The molecular weight of the polymer was Mn = 78 000 with a dispersity of Mw/Mn =1.2.
Elemental analysis of PTVE: C, 65.9; H, 9.9; and N, 6.8; Calcd. for C11H20NO2: requires C,
66.6; H, 10.1;and N, 7.1. The PTVE was chemically reduced with phenylhydrazine, and
characterized by NMR spectroscopy. δH (500 MHz; CD3CN; Me4Si) 3.85 (1 H, m, piperidine
CH), 3.68 (1 H, br s, OCHCH2), 1.93 (2 H, m, piperidine CH2), 1.79 (2 H, m, piperidine CH2),
1.32 (2 H, br s, OCHCH2), 1.11 (6 H, s, 2 × CH3), 1.10 (6 H, s, 2 × CH3); δC(500 MHz;
CD3CN; Me4Si) 20.7, 33.1, 48.9, 59.6, 63.1, 74.8, 75.6.
Determination of the Radical Content
PTVE was characterized by the g value (2.0067) of the ESR signal, which was in
agreement with that of TEMPO. The radical concentrations were determined, assuming that
the polymer was paramagnetic at room temperature, by comparing the integrated ESR
intensity with that of the TEMPO powder as the standard. The radical concentration was also
determined by means of SQUID measurements using the Curie-Weiss plot. The two
independently determined values agreed well each other.
Electrode Preparation and Electrochemical Measurements
The acetonitrile solutions of PTVE (10‒50 g/L) were spin-coated on a current collector
such as a glassy carbon substrate, followed by drying at 80˚C for 24 hr under vacuum, to yield
the PTVE film with a thickness of 35 nm‒1 μm, respectively.
The electrochemical measurements were performed using a conventional three-electrode
cell under standard ambient condition. A normal potentiostat system (BAS Inc. ALS660B)
was used for the cyclic voltammetry, chronopotentiometry and other electrochemical
measurements. A coiled platinum wire and Ag/AgCl were used as the counter and reference
electrode. The cyclic voltammogram was measured in a 0.1 M NaCl aq., NaBF4 aq., and
NaPF6 aq.. Their pH were controlled adding HCl and NaOH.
The chronopotentiometry were measured in 0.1 M NaCl aq., NaBF4 aq. and NaPF6 aq. (1)
Cycle performance test: the PTVE half cell was charged and discharged at 60 C repeatedly
until 1000 cycles. (2) Charging rate performance test: the PTVE half cell was charged at the
60‒1200 C-rate, and its discharging capacity was measured at 60 C. (3) Discharging rate
performance test: the PTVE half cell, fully charged at 60 C, was discharged at a 60‒1200

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Redox Properties of TEMPO Substituted Polyvinylether on Electrolytes
and its Battery performance of the Test-Cell with Zinc Anode
- 63 -
C-rate, and the discharging capacities were measured.
An impedance spectrum analyzer (Solartron SI 1260) with ZPlot software was employed
to measure the ac-impedance of three types of half-cells composed of the PTVE layer and the
respective electrolytes. The ac potential amplitude was set at 10 mV and the frequencies
ranged from 0.01‒2500 Hz.
Cell Fabrication and Battery Performance
A test full-cell was fabricated using the PTVE layer on a glassy carbon substrate as the
cathode and a zinc anode in an aqueous solution of 0.1 M ZnCl2 and 0.1M NH4Cl.
Charging-discharging capacities and output voltage of the cell were tested by
chronopotentiometry at 60 C. The cycle performance of the cell was examined by repeating
charging-discharging galvanostatic cycles at 60 C. The cutoff potentials were 1.4 and 2.0 V vs.
Zn/Zn2+.
Other Measurements
The 1H- and 13C NMR spectra were recorded using a JEOL Lambda 500 or Bruker
AVANCE 600 spectrometer, and Gel permeation chromate graphy was performed with DMF
using a Tosoh HLC-8220 instrument. Electron spin resonance (ESR) spectra were obtained
using a JEOL JES-TE200ESR spectrometer with 100 kHz field modulation. The
magnetization and magnetic susceptibility of the powder polymer sample were measured by
Quantum Design MPMS-7SQUID (superconducting quantum interference device)
magnetometer. The magnetic susceptibility was measured from 10 to 300 K in a 1.0 T field.
Refarences
[1] G. I. Likhtenshtein, J. Yamauchi, S. Nakatsuji, A. I. Sminov, R. Tamura, Nitroxides 2008.
[2] R. A. Sheldon, I. W. C. E. Arends, G. J. T. Brink, A. Dijksman, Accounts Chem. Res. 2002,
35, 774.
[3] P. J. Wright, A. M. English, Journal of the American Chemical Society 2003, 125, 8655.
[4] H. Nishide, S. Iwasa, Y. J. Pu, T. Suga, K. Nakahara, M. Satoh, Electrochim. Acta 2004,
827.
[5] H. Nishide, T. Suga, Electrochem. Soc. Interface 2005, 14, 32.
[6] T. Suga, H. Konishi, H. Nishide, Chem. Commun. 2007, 1730.
[7] T. Suga, Y. J. Pu, S. Kasatori, H. Nishide, Macromol. 2007, 40, 3167.
[8] Y. Yonekuta, K. Oyaizu, H. Nishide, Chem. Lett. 2007, 36, 866.
[9] H. Nishide, K. Oyaizu, Science 2008, 319, 737.
[10] K. Oyaizu, Y. Ando, H. Konishi, H. Nishide, J. Am. Chem. Soc. 2008, 130, 14459.
[11] K. Oyaizu, T. Suga, K. Yoshimura, H. Nishide, Macromol. 2008, 41, 6646.

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[12] K. Koshika, N. Sano, K. Oyaizu, H. Nishide, Chem. Commun. 2009, 836.
[13] K. Koshika, N. Sano, K. Oyaizu, H. Nishide, Macromol. Chem. Phys. 2009.
[14] D. R. Lide, in Handbook of Chemistry and Physics, 72nd edition, CRC Press, Boston,
1991, p. 96.
[15] J. R. Fish, S. G. Swarts, M. D. Sevilla, T. Malinski, J. Phys. Chem. 1988, 92, 3745.
[16] Y. Kato, Y. Shimizu, Y. J. Lin, K. Unoura, H. Utsumi, T. Ogata, Electrochimica Acta
1995, 40, 2799.

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Chapter 4 Safety Assessment s of the Radical Polymers for Battery
Electrode
4.1 Introduction
4.2 Cathode Performance Evaluation
4.3 Disaster Safety Assessment
4.4 Health Safety Assessment
4.5 Experimental Section
References

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4.1 Introduction
Research on devices for electrical energy storage has currently received significant
attention.[1-4] Rechargeable or secondary batteries, such as lithium ion batteries, are very
popular and being used in portable electronic devices, such as mobile phones, laptop PCs, and
digital cameras, and could also be used in electric vehicles, for electric storage and in solar-
and wind-energy converters. Secondary batteries have been regarded as an environmentally
benign technology because of their rechargeability which contributes to reducing the amount
of discarded primary batteries. However, secondary batteries still remain immature from the
view points of green chemistry, i.e., limited metal resources, tedious waste treatment
processes, and safety concerns (disaster and health). Some electrode-active materials in
conventional batteries have been made from rare metals such as cobalt, manganese and
nickel.[3] The used batteries were collected in large-amounts at least in Japan, but most of
them have been landfilled (only part of them was recycled for the metals).[5, 6] Finally, some
secondary batteries, such as Li-ion and Ni-Cd, are encountering over-heating problems and
the tightening of regulation issues of hazardous substances, respectively. The over-heating
problems were caused by the combination of the exothermic electrode reaction and the ion
conduction in organic electrolytes, sometimes resulting in a series of ignition accidents.[4]
Indeed, in 2007 and 2008, Panasonic and Sony encountered serious recalls of their 46 and 0.1
million Li-ion batteries for mobile phones and laptops, respectively.[7, 8] The regulations
against hazardous substances have become stricter on a global scale. In the European Union,
Restriction on Hazardous Substances (RoHS) restricted the use of six hazardous materials,
such as lead, mercury and cadmium, in the manufacture of various types of electronic and
electrical equipment (except batteries) in 2003. The directive 2006/66/EC then restricted the
amount of mercury and cadmium contained in batteries in 2006. After the start of the directive,
most batteries with a certain mercury or cadmium content will be prohibited from the mercket.
Many manufacturers dealing with such hazardous substances started to prepare for their
replacement.
We have studied electrode-active polymers using robust radicals for organic-based
secondary batteries as one of the solutions to the problems.[9-11] We have focused our attention
on the redox property of the robust radicals, synthesizing a series of aliphatic polymers
bearing the pendant robust radical groups (we called them radical polymers) and utilizing
them as organic electrode-active materials.[12-18] The radical polymers, synthesized from less
limited petroleum feedstock, have the possibility to alleviate the above resource problem and
to allow a simple treatment process by incineration disposal. However, previously reported
battery configurations with radical polymers and an organic electrolyte, such as poly(2,2,6,6,-
tetramethylpiperidinyloxy-4-yl methacrylate) (PTMA) and an acetonitrile solution containing
tetrabutylammonium[12] still retained the potential risk of ignition, thus requiring a built-in

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Safety Assessment s of the Radical Polymers for Battery Electrode
- 67 -
safety system like the lithium-ion battery.[4] This is because the previously reported radical
polymers showed a hydrophobic character, not working in aqueous electrolytes.
According to the twelve principles of green chemistry, it is better to prevent waste than to
treat or clean up waste after it is formed.[19, 20] Recently, the author designed a hydrophilic
radical polymer, poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl vinylether) (PTVE), which
sufficiently functioned even in an aqueous electrolyte, and reported the following electrode
performance [21, 22]: (i) High charging and discharging capacity of 131 mAh g-1 ascribed to the
stoichiometric redox of the radical moieties, (ii) Long cycle life, often exceeding 1000 cycles,
derived from the chemical stability of the radicals and from the amorphous electrode structure,
and (iii) High charging-discharging rate performance (1200 C) resulting from the rapid
electron-transfer process of the radical moiety and the high equivalent electrical conductivity
of the aqueous electrolyte on the order of 10-2–10-3 m2 S mol-1, which is 10-times higher than
that of organic electrolytes.[23] (The rate of 1 C is defined as the current density at which the
charging or discharging of the cell takes 1h. Most conventional batteries function during the
charging or discharging at 1–2 C.) An important issue described in this report is that a
combination of hydrophilic radical polymer and aqueous electrolyte allowed an organic
electrolyte-free battery design and a rapid charging-discharging performance at the same time.
Previous papers [21, 22] have discussed only the electrode performance, without evaluating the
safety of the radical polymer-electrode. One could assume that such a battery configuration
has inherent advantages in terms of many aspect of green chemistry. In this paper, the author
report, for the first time, the disaster and health safeties of the hydrophilic radical polymer as
a preliminary assessment at the early development stage. The safety was studied along the
i-Messe[24], an evaluation method proposed by the committee of the Green Sustainable
Chemistry Network Japan.
Figure 4.1 Aqueous electrolyte-type radical polymer battery

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Chapter 4
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4.2 Cathode Performance Evaluation
Cathode performance of PTVE was compared with those prepared with PTMA and
lithium cobalt oxide by measuring charging-discharging rate, rechargeable cycle and electro
motive force against the standard reference anode. As for the performance of lithium ion
battery the specifications given by an relevant literature[25] was used and given on the list for
the purpose of having appropriate level of performances.
Aqueous Electrolyte Type Radical Polymer Battery Cathode: PTVE
The chemical structure of PTVE is composed of hydrophilic polyvinyl ether-backboned
polymer and TEMPO pendant group. It gave a reversible one-electron oxidation capability
even in aqueous electrolytes. PTVE prepared and used in this study, gave a redox wave at
1.7 V vs. Zn/Zn2+. The capacity of PTVE remained more than 80% of initial level after
1000 charging-discharging cycles. The charging-discharging rate performance of PTVE was
1200 C (corresponding to the full charging and discharging for 3 seconds, respectively).
Organic Electrolyte Type Radical Polymer Battery Cathode: PTMA
PTMA is composed of lipophilic polymethacylate-bacakboned polymer and TEMPO
pendant group. The PTMA used in this study gave a redox wave at 3.6 V vs. Li/Li+. The
capacity of PTMA remained more than 95% of initial level after 1000 charging-discharging
cycles. The charging-discharging rate performance of PTMA was 12 C (corresponding to the
full charging and discharging for 5 minutes, respectively).
Li-ion Battery Cathode: Lithium Cobalt Oxide
Lithium cobalt oxide has 3.7 V of electro motive force vs. graphite carbon. The capacity
remained more than 75% of initial capacity after 500 charging-discharging cycles. The
charging-discharging rate performance was 2 C (corresponding to the full charging and
discharging for 30 minutes, respectively).
Table 4.1 Comparison of cathode performances

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Safety Assessment s of the Radical Polymers for Battery Electrode
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4.3 Disaster Safety Assessment
Along the i-Messe, an evaluation method, the impact for safety was divided into two
categories: “Disaster safety” and “Health safety”, the safety impact of the cathode-active
materials were evaluated as two objects: “production, usage and disposal” and “raw material”.
The
author
selected
three
electrode-active
materials:
poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl
vinylether)
(PTVE),
poly(2,2,6,6,-tetrametylpiperidine methacrylate) (PTMA) and lithium cobalt oxide as cathode
active material of aqueous electrolyte-type radical polymer battery, organic electrolyte-type
radical polymer battery and lithium ion battery, respectively.
Electrode active material, during the use and upon disposal
PTVE and PTMA were considered basically to be low potential risks causing disaster
hazards. PTVE and PTMA are chemically stable, no explodability, flammability and
pyrophoric property. The polymers have a low reactivity toward oxygen and water, remaining
unchanged with no decomposition and deactivation under ambient conditions over 1 year. The
polymers are also thermally stable. Their10% decomposed temperatures are higher than
200°C. This is sufficiently higher than envisioned operating temperature of the battery.
During the use and disposal, the polymers are also low potential risks causing disaster hazards.
Unlike lithium cobalt oxide, the redox reaction of the polymers is fundamentally
non-exothermic. The redox reaction of lithium cobalt oxide includes the lattice transformation
with heat generation. On the other hand, the structural change of TEMPO unit between
nitroxide radical and oxoammonium cation is very slight. This reduces the risk of overheating.
In addition, considering combination of electrolyte solution, PTVE is considered lowest risk
potential of ignition and explosion because of combination of non-exothermic electrode and
aqueous electrolyte solutions. The polymers demonstrated quantitative coulombic efficiency
and high rechargeability. This result means the redox reaction of TEMPO has no side
reactions and both the polymers in charging state and discharging state have low reactivity
toward electrolyte salts and solutions. Therefore the PTVE and PTMA have a low possibility
to generate heat, gasses and exploitive materials. During the disposal, the polymers are simply
burned and generate CO2, NO2 and H2O. It was estimated essentially not much difference
with the disaster risk between the radical polymer cathodes and conventional lithium cobalt
oxide.

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Materials used for the synthesis
Among the row materials in three syntheses, organic solvent was considered to be highest
disaster risk material. In polymer synthesis process, organic solvents were used as reaction
solvent. Some organic solvents, such as THF and toluene, showed the risk phrase of R-11
(high flammable). They require careful handling, however, the author estimated the actual
ignition risk was within the acceptable range.
Table 4.2 Disaster safety assessment of PTVE, PTMA and Lithium cobalt oxide
4.4 Health Safety Assessment
Electrode active materials, during the use and upon disposal
PTVE and PTMA were considered basically to be non-toxic and low potential risks
causing health hazards during the use and disposal. PTVE and PTMA have a low
bioavailability as well as most of general polymers. The polymers are nonvolatile and
insoluble for general solvents except for a few kinds of organic solvents such as acetonitrile,
DMSO. i.e. the polymers had low possibility to enter the human body through the
respiratory tract and skin. During the use, the polymers have low possibility of generating
secondary toxic materials because of their stability as referred to above. For the disposal,
they are burned and generate NOx. However NOx gases are recovered by incineration
system.
Materials used for the synthesis
In this study, the electrode active materials, PTVE and PTMA, were synthesized by the
following three steps as shown in Scheme 4.1–4.3. Among the row materials, boron
trifluoride diethyl etherate, the initiator of polymerization was estimated as the materials of

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Safety Assessment s of the Radical Polymers for Battery Electrode
- 71 -
highest toxicity. It gave TPI (Toxic Potential Indicator by Fraunhofer Institute IZM) of as
high as 47 mg-1. However, the author estimated the actual toxicity was within the acceptable
range because the usage amount of boron trifluoride diethyl etherate was as low as 2 mol%
of the monomer.
Table 4.3 Safety assessment of PTVE, PTMA and Lithium cobalt oxide
In summary, a hydrophilic radical polymer cathode was designed, prepared and evaluated
based the concept of Green and Chemistry. The basic cathode performances were compared
with the organic electrolyte-type radical polymer battery cathode and the lithium ion battery
cathode. Preliminary evaluation along the i-Messe showed substantial improvements with the
health safety and disaster safety as well as environmental impacts upon disposal. The
preliminary results of cathode performances showed that a higher recharging rate, exceeding
1000 recharging cycle number and 1.7 V of electro motive force. These results supported
strongly that aqueous electrolyte-type radical polymer battery promises to be safer and the
next generation secondary battery with highly improved Green Chemistry profiles and
electrode performances.

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Chapter 4
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4.5 Experimental Section
Synthetic procedures
PTVE
2,2,6,6-Tetrametylpiperidne-N-oxyl-4-vinyl ether was synthesized as the monomer to
yield, prepared by using coupling reaction of 4-hydroxy-2,2,6,6-tetrametylpiperidne- N-oxyl
and vinyl acetate, according to the previous paper. The vinyl monomer was polymerized via
cataionic polymerization in dichloromethane with boron trifluoride diethyl etherate, as the
initiator at -25°C.
Scheme 4.1 Synthesis of PTVE
PTMA
The precursor of PTMA monomer (2,2,6,6,-tetrametylpiperidine methacrylate) was
polymerized by radical polymerization in THF with 2,2’-azobisisobutyronitrile as the radical
initiator at 80°C. The precursor polymer was treated with 3-chloroperoxybenzoic acid to yield
PTMA at room temperature.
Scheme 4.2 Synthesis of PTMA
Lithium cobalt oxide
Lithium cobalt oxide prepared by heating stoichiometric mixture of lithium carbonate and
cobalt(II,III) oxide at 800 °C in air for 20 h.
Scheme 4.3 Syntesis of lithium cobalt oxide
Formulation and preparation of electrode
PTVE cathode
A film electrode was prepared by following procedure. The acetonitrile solutions of

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Safety Assessment s of the Radical Polymers for Battery Electrode
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PTVE were spin-coated on a current collector such as a glassy carbon substrate, followed by
drying at 80˚C for 24 hr under vacuum, to yield the PTVE film with a thickness of 60 nm.
PTMA cathode
A carbon-composite electrode (1.2 mg/cm2) was prepared by following procedure. 10
milligrams of the radical polymer, PTMA, and 80 mg of graphite (carbon fiber prepared in
gas-phase: VGCF, Showa Denko Co.) were mixed with 10 mg of binder powder
(polyvinylidenefluoride resin: KF polymer, Kureha Chemical Co.) in the presence of a solvent.
The resulting black clay was spread onto a current collector such as aluminum plate, followed
by drying at 80˚C for 24 hr under vacuum.
Referenece
[1] G. Pistoia, "Batteries For Portable Devices ", Elsevier Amsterdam, 2005.
[2] B. Scrosati, W. A. V. Schalkwijk, "Advances in Lithium-Ion Batteries", Plenum
Publishers, 2002.
[3] R. J. Brodd, K. R. Bullock, R. A. Leising, R. L. Middaugh, J. R. Miller, E. Takeuchi, J.
Electrochem. Soc. 2004, 151, K1.
[4] P. G. Balakrishnan, R. Ramesh, T. P. Kumar, J. Power Sources 2006, 155, 401.
[5] "Report from Ministry of Economy, Trade and Industry Japan: Yearbook of Machinery
Statistics ", 2008.
[6] "Report from Japan Portable Rechargeable Battery Recycling Centor:
http://www.jbrc.net/recycle/recycle/index.html".
[7] "The Wall Street Journal Oct 30, 2008".
[8] "The Wall Street Journal Aug 14, 2007".
[9] H. Nishide, K. Oyaizu, Science 2008, 319, 737.
[10] H. Nishide, K. Koshika, K. Oyaizu, Pure and Applied Chemistry 2009.
[11] K. Oyaizu, H. Nishide, Adv. Mater. 2009.
[12] H. Nishide, S. Iwasa, Y. J. Pu, T. Suga, K. Nakahara, M. Satoh, Electrochim. Acta 2004,
827.
[13] H. Nishide, T. Suga, Electrochem. Soc. Interface 2005, 14, 32.
[14] T. Suga, H. Konishi, H. Nishide, Chem. Commun. 2007, 1730.
[15] T. Suga, Y. J. Pu, S. Kasatori, H. Nishide, Macromol. 2007, 40, 3167.
[16] K. Oyaizu, Y. Ando, H. Konishi, H. Nishide, J. Am. Chem. Soc. 2008, 130, 14459.
[17] K. Oyaizu, T. Suga, K. Yoshimura, H. Nishide, Macromolecules 2008, 41, 6646.
[18] T. Suga, H. Ohshiro, S. Sugita, K. Oyaizu, H. Nishide, Adv. Mater. 2009, 21, 1627.
[19] P. T. Anastas, J. C. Warner, "Green chemistry: Theory and Practice", Oxford University

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Press, New York.
[20] P. T. Anastas, M. M. Kirchhoff, Accounts Chem. Res. 2002, 35, 686.
[21] K. Koshika, N. Sano, K. Oyaizu, H. Nishide, Chem. Commun. 2009, 836.
[22] K. Koshika, N. Sano, K. Oyaizu, H. Nishide, Macromol. Chem. Phys. 2009.
[23] D. R. Lide, in Handbook of Chemistry and Physics, 72nd edition, CRC Press, Boston,
1991, p. 96.
[24] I. Yasui, T. Goto, M. Kitajima, Y. Naito, "Proposal for a New Evaluation Method for
Green & Sustainable Chemistry", in AIChe Annual Meeting 2005, Cincinnati, Ohio, USA,
2005.
[25] "Sanyo Mobile Energy Company specification document:
http://battery.sanyo.com/product/lithum-ion/pdf/02/UF383543F.pdf ".

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Chapter 5
Battery Performance and Green Evaluation of Organic Secondary
Battery Fabricated with Radical Polymers and Aqueous Electrolyte
5.1 Introduction
5.2 Synthesis of Viologen Polymer for Anode-Active Material
5.3 Electrochemical Properties of Viologen Polymer
5.4 Battery Performance of the Organic Secondary Battery
5.5 Green Evaluation for the Organic Secondary Battery
5.6 Experimental Section
References

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5.1 Introduction
Studies of high-performance charge-storage devices similar to lithium-ion batteries are of
great interest.[1-3] The author have previously studied organic secondary batteries that use
polymer electrodes and whose operation is based on the redox property of stable radicals.
Among the suitable stable radicals, nitroxide radical molecules, such as
2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), are known to exhibit a reversible redox
property in both organic and aqueous solutions.[4, 5] A series of aliphatic polymers bearing the
pendant nitroxide radical groups have been synthesized and used as electrode-active or
charge-storage materials.[6-16]
The organic secondary battery composed of the radical polymer electrodes demonstrate
several advantages over other organic-based batteries: (i) a high charging and discharging
capacity (>100 mAh/g), ascribed to the stoichiometric redox of the radical moieties, (ii) a
high-charging and -discharging rate performance resulting from the rapid electron-transfer
process of the nitroxide radical species, and (ii) a long cycle life, often exceeding 1000 cycles,
derived from the chemical stability of the radicals and from the amorphous electrode
structure.
Previous studies on the radical polymer batteries report that electrode-active polymers
have a lipophilic character. Organic electrolytes are highly compatible with the polymers and
are therefore suitable media for supplying charge-compensating ions to active sites of the
lipophilic radical polymers in the electrode. Thus in radical polymer batteries, the
compatibility between the electrolyte and electrode-active polymer is very important in
influencing battery performance. Any degree of incompatibility shortens the
charge-compensating ion supply and thus reduces the charging-discharging capacity of the
battery. Therefore from the view point of the compatibility, water has never been studied as
the electrolyte of radical polymer battery. However, batteries fabricated with radical polymer
electrodes in aqueous electrolytes are expected to show improved charging-discharging rate
performance. This is because aqueous electrolytes possess ten-times-higher equivalent
electrical conductivity than organic electrolytes allowing rapid charge diffusion within the
polymer. In addition, such batteries are also expected to reduce ignition and/or explosion risk
due to their organic-solvent-free design.
The molecular design of electrode-active polymer for use in aqueous electrolyte must
address two issues: (1) some radical polymers have a low degree of compatibility with water
and (2) some radical molecular are unstable in water. We therefore designed a hydrophilic
radical polymer poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl vinylether) (PTVE) to address
these issues. PTVE is composed of a hydrophilic polyvinylether-backboned polymer and a
TEMPO pendant group with stable redox capability even in aqueous electrolytes. Due to its

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functional and compact molecular design, PTVE exhibits a high formula-weight-based
charging-discharging capacity per weight of 135 mAh g-1, which has improved from those of
conventional redox polymers, such as polyvinylferrocene[17]
and polybutylviologen
dibromide,[18]
was even higher than that of the previously reported
poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl methacrylate) (PTMA) (111 mAh g-1)[6] by our
group. In this chapter, the author report on the synthesis and electrochemical properties of
polydecylbilogen (PV10) and the performance of a prototype test cell fabricated with PTVE
cathode, PV10 anode, and aqueous electrolyte. In addition, green characteristics of the totally
organic radical battery were evaluated using i-Messe, an evaluation method proposed by the
committee of the Green Sustainable Chemistry Network Japan. According to the i-Messe, the
green characteristics were evaluated by comparing with semi-organic model radical polymer
battery composed of PTVE cathode, zinc anode and ZnCl2-NH4Cl aq. from the view point of
environmental compatibility, safety and socio-economic impact. The i-Messe had an
advantage over the life cycle assessment. Life cycle assessment is one of the well known
green evaluation method. However life cycle assessment requires strictly quantitative
evaluation. On the other hand, i-Messe allow evaluating their green characteristics by
comparing. Therefore the i-Messe is easy to apply the research in early development stage.
5.2 Synthesis of Viologen Polymer for Anode-Active Material
5.2.1 Polymer Design and Synthesis
Poly(decyl viologen) (PV10) was designed as an suitable anode-active polymer for
utilizing with PTVE. PV10 also has a redox capability in water under neutrality condition.
(polyquinone exhibits stable redox capability only in strong basic condition) The redox
potential of PV10 is -0.6 V (vs. Ag/AgCl), which is expected to demonstrate 1.3 V of output
voltage. (The redox potential of polyviniferocen is 0.7 V (vs. Ag/AgCl) similar to PTVE.)
PV10 with a molecular weight of Mn = 5000 (Mw/Mn = 1.1) was synthesized by
Menschutkin reaction of 4,4’-bipyridine and 1,10-dibromodecane. The obtained polymer was
soluble in water. To fix on the current collector, the polymer was complexed with poly(styrene
sulfonate) with a molecular weight of Mw = 75000. The polymer complex was dissolved in a
mixture of HCl, water and dioxane in a weight ratio of 5:50:45, and spin-coated on to glassy
carbon substrate, followed by drying at 80°C for 24 h under vacuum.
Scheme 5.1 Synthesis of PV10.

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5.2.2 Thermal Properties
Thermal analysis of the PV10 and PV10-PSS powder sample revealed that PV10 and
PV10-PSS themselves were stable up to around 240 and 300°C: The 10%-decomposition
temperatures were 257 and 312°C, respectively (Figure 5.1). The complex formation of
PV10-PSS gave a thermal stability. Both polymers had a sufficient thermal stability in the
range of electrode applications.
Figure 5.1 Relative concentration of unpaired electrons (●) and relative weight (—) of the powder
sample of PTVE. Inset: DSC thermogram.
5.3 Electrochemical Properties of Viologen Polymer
5.3.1 Redox Properties
The cyclic voltammogram of the PV10-PSS film repeatedly displayed a chemically
reversible redox wave at -0.50 vs. (Ag/AgCl) in a 0.1 M NaCl aq. at pH 6.2 (Inset of Figure
5.2). The redox capacity was almost agreed with molecular weight based calculated capacity
of 40 mAh g-1. In neutrality, weakly acidic and basic condition with pH 3–11, PV10-PSS
demonstrated stable redox ability and obtained almost quantitative redox capacity respectively
(Figure 5.2). In acidic condition with pH of less than 3, PV10-PSS was soluble in electrolyte
because of their dissociation. On the other hand, in basic condition with pH of more than 12,
PV10-PSS demonstrated redox wave attenuation with a voltage sweep.
Scheme 5.2 Redox couple of PV10

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Figure 5.2 Cyclic voltammogram of the PTVE layer with a thickness of 60 nm coated on a glassy
carbon substrate in 0.1 M aqueous NaCl. Inset: Redox capacity relative to pH
5.3.2 Charging-discharging Cycle Performance
The charging-discharging curves of the half cell exhibited a plateau voltage at -0.5 V vs.
Ag/AgCl (Figure 5.3), which nearly agreed with the redox potential of the PV10-PSS film
(-0.50 V) shown in Figure 5.3. The charging-discharging capacity almost coincided with each
other at ca. 40 mAh g-1 and agreed with the calculated capacity obtained in the Figure 5.3.
The cycle performance of the charging-discharging at the cut-off voltages of 0–-0.8 V and
C-rate of 60 C is shown in inset of Figure 5.3. The coulombic efficiency, i.e., discharging
capacity vs. charging capacity, is maintained at almost 100% even after 100
charging-discharging cycles, indicating that the charged species, the viologen mono cation
form of PV10-PSS, stoichiometrically contributed to the following discharging process.
Figure 5.3 Charging-discharging curve of PV10-PSS film in 0.1 M NaCl aq. at 60 C. Inset:
Discharging capacity on the charging-discharging cycle number.

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However, the discharging capacity decreases to ca. 40% of the initial value after 100 cycles,
suggesting partial elution out of the PV10-PSS into the electrolyte (which could be impeded
through slight crosslinking of the polymer).
5.3.2 Charging-discharging Rate Performance
The PV10-PSS half-cell using 0.1 M NaCl aq. was charged at a 60–1200 C-rate and then
discharged at 60 C to examine the charging rate performance (Figure 5.4). The coulombic
efficiency (discharging capacity over the charging capacity) was maintained at almost 100%
from 60 to 1200 C. This result means that the charging rate performance was able to be
evaluated with charging capacity. The charging capacity gradually decreased to 40% of the
initial capacity at 600 C (Inset of Figure 5.4).
Figure 5.4 Charging-discharging rate performance of PV10-PSS film. Inset: Relative
capacity on charging-discharging rate.
5.4 Battery Performance of the Organic Secondary Battery
The test-cell was fabricated with PTVE film (60 nm) cathode, PV10 complex anode (100
nm) anode, and 0.1 M NaCl aq.. As a reference, another cell was fabricated with PTVE film
(60 nm) cathode, zinc plate anode and 0.1 M ZnCl2 and 0.1M NH4Cl. The author called them
“organic model” and “semi-organic model”, respectively.
5.4.1 Charging-discharging property and its cycle performance
In charging-discharging performance test at C-rate of 60 C, organic model and
semi-organic model exhibited output voltage of 1.3 V and 1.7 V (inset of Figure 5.5), which
agreed with the difference of the redox potentials of between PTVE and PV10, PTVE and
zinc, respectively. The discharging capacities of both organic model and semi-organic model
displayed ca. 131 mAh g-1 and agreed with a maximum effective charging–discharging
capacity per weight (2.8 mC cm-2 × 60 nm thickness). The cycle performance of the

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discharging capacities of the organic model, semi-organic model, and half-cell of PTVE at
C-rate of 60 C is shown in Figure 5.5. The three discharging capacities of PTVE were
gradually decreased with cycle number similaly until 150 cycles. Then discharging capacity
of semi-organic model was continued to decrease to ca 60% of initial capacity until 500
cycles. On the other hand, discharging capacity attenuation of half-cell and organic model
were gradually reduced. After 1000 cycle, more than ca. 65% of initial capacity were
remained. In case of semi-organic model, white precipitation of zinc hydroxide was gradually
generated with increasing cycle number. The precipitation could influence on the decreasing
capacity. On the other hand, electrolyte of organic model was clear and no precipitation. The
PTVE cathode in organic model demonstrated high cycle performance similar to in half-cell.
Figure 5.5 Discharging capacities for organic model (●), semi-organic model (o), half-cell (○)
on the charging–discharging cycle number. Inset: Discharging curves of the three cells.
5.4.2 Charging-discharging Rate Performance
The charging-discharging rate performance of the organic model, semi-organic model,
and half-cell of PTVE are shown in Figure 5.6. The capacity of the half-cell charged and
discharged even at 1200 C (corresponding to the full charging for 3 seconds) retained at 97%
(127 mAh g-1) of the calculated capacity. However, the charging-discharging capacities of
both organic model and semi-organic model decreased with increasing C-rate. These results
means that charging-discharging speed of viologen and zinc are slower than that of PTVE.
Especially redox process of zinc contains morphological modification between metal solid
and ion. On the other hand, the redox process of viologen has only molecular structural
change, no morphological modification. Therefore in organic model, twice higher of
charging-discharging capacities were remained at more than 240 C. Optimization of the
molecular design of viologen polymer such as “shorten the distance of redox active site” will

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lead to demonstrate higher charging-discharging rate performance.
Figure 5.6 Charging-discharging capacities for organic model (●), semi-organic model ( ), half-cell
(○) on the charging–discharging rate.
5.5 Green Evaluation for the Organic Secondary Battery
The green characteristics of organic model were evaluated along with “i-Messe”. The
baudary condition was set 4 process, such as material production, fabrication, usage, and
disposal. The evaluation results are summerized in Figure 5.7 These results were expressed by
relative comparison with semi-organic model as a standard. Smaller daimond shape means
improvement of impacts.
Figure 5.7 i-Messe evaluation of organic model comparing with semi-organic model
For environment impact and safety impact, major advantages of organic model were
found in three evaluation item: ‘Waste volume’, ‘Emission to environment’, and ‘Health
safety of production, usage, and disposal’. Alternation of zinc and zinc chloride reduced
directly the health safety (production, usage and disposal) risk and heavy metal emission to

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environment. In addition, heavy metal free design allow incineration disposal, reducing waste
volume. On the other hand, major disadvantages were found in four evaluation item: ‘Energy
consumption’, ‘Material consumption’, ‘Health safety of raw material’, and ‘Disaster safety’.
Organic model has synthesis process of the viologen. This process consumed the extra energy
and material. This extra material increased the health safety risk and disaster safety risk.
However, material consumption will be improved by synthesis process optimization, which
also reduces the safety risks. For socio-economic impact, ‘Social, regional loss’ was decreased
by risk reduction of water pollution and ground pollution. ‘Producer’s demerit’ was also
decreased by intellectual property and good corporate image. The evaluation details described
as below.
5.5.1 Environmental Impact
Energy consumption
Energy consumption, such as electrical power, steam and fuel consumption, for
organic model were evaluated qualitatively in each process. In material production process,
increased energy consumption was estimated due to the added PV10 synthesis process. In
process of use and disposal, energy consumptions for organic model were considered to be
same level. Main energy consumption in use process was charging. Charging efficiency of
the organic model and semi-organic model was same level. On the other hand, main energy
consumption in disposal process was incineration. The consuming energy was considered
to be almost same. In fabrication process, energy consumption should be reconsidered
appropriate timing, but at the current status there is little difference between organic model
and semi-organic model.
Emission to environment
Impact of organic model on ‘Emission to environment’ was estimated as follows.
‘Emission to environment’ was improved in disposal process and was comparable in other
three processes. In disposal process, emission amount from both batteries were assessed on
the assumption that metals and electrolyte salts remained as ash, and polymer changed to
carbon dioxide and nitrogen dioxide. In this case, target substances were zinc and nitrogen
dioxide. Incineration disposal of organic model emitted 280 mg of nitrogen dioxide. On the
other hand, incineration disposal of semi-organic model emitted 120 mg of nitrogen
dioxide and 1 g zinc. This decreased emission amount was derived from the metal-free
design of organic model.
Material consumption
Impact of organic model on ‘Material consumption’ was estimated as follows. Material

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consumption was increased in material production process and comparable in other three
processes. Material consumption of organic model and semi-organic model were 57.9 g
and 48.7 g, respectively. Material production including synthesis consume mach amount of
raw materials. This result indicated that optimization of synthesis process was required.
Waste volume
Impact of organic model on ‘Waste volume’ was estimated as follows. Waste volume
was decreased in disposal process and comparable in other three processes. In this case,
target substances were zinc and electrolyte salt. Incineration disposal of organic model
wasted 58 mg of electrolyte salt. On the other hand, incineration disposal of semi-organic
model wasted 190 mg of electrolyte salt and 1 g zinc. This decreased waste volume was
derived from the metal-free design of organic model.
Table 5.1 Environmental impact
5.5.2 Safety Impact
Health safety—product
Product-Health safety in organic model was substantially improved. TPI-value of
organic model reduced to zero, because replacement of zinc, zinc chloride and ammonium
chloride to PV10 and sodium chloride. Zinc, zinc chloride and ammonium chloride are
known as toxic potential materials such as, very toxic to aquatic organisms, may cause
long-term adverse effects in the aquatic environment, harmful if swallowed, causes burns,
and irritating to eyes.
Health safety—raw materials
Raw materials-Health safety in organic model decreased. Organic model showed TPI-
value of 8.0×105 ,which was higher than semi-organic model of 6.1×105. This was
derived from usage of Methanol and DMF in synthesis of PV10. Toxicity of Methanol is
known as follows: danger of very serious irreversible effects through inhalation, in contact
with skin and if swallowed. DMF is also known as follows: May cause harm to the unborn
child, Harmful by inhalation and in contact with skin, and Irritating to eyes.

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This result indicated that synthesis process optimization including reconsideration of
reaction solution selection was required.
Disaster safety—product
For product disaster safety, organic model and semi-organic model gave 0 TPI. This
means both model were composed without the materials possessing disaster risks. In
predictive disasters for batteries, one of the most serious disaster problems was ignition or
explosion accidents. These accidents were caused in lithium ion batteries, which composed
of high exothermic electrode and flammable organic electrolyte. On the other hand,
organic model and semi-organic model utilized aqueous electrolyte, decreasing the ignition
and explosion risks.
Disaster safety—raw materials
Raw materials –disaster safety in organic model also decreased. Organic model showed
TPI- value of 4.0×105, which was higher than semi-organic model of 2.8×105. The main
reason of this incensement was derived from methanol for polymer synthesis.
Table 5.2 Safety impact
5.5.3 Socio-Economic Impact
Global, ecosystem loss
Global, ecosystem loss was evaluated from the view point of 5 items: (1) global
warming, (2) ozone depletion, (3) energy consumption, (4) exhaustible resources, and (5)
recyclable resources. These evaluation results were summarized in Table 5.3. It was
particularly worth noting that organic model reduced usage amount of exhaustible
resources and increase emission amount of carbon dioxide by incineration disposal.
Social, regional loss
Social, regional loss was evaluated from the view point of 5 items: (1) air pollution /
acidification, (2) water pollution / eutrophication, (3) land pollution, (4) emission of waste,

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and (5) effect on regional society. These evaluation results were summarized in Table 5.3.
It was particularly worth noting that organic model reduced water pollution substance, land
pollution substance and waste volume.
Users’ demerit
Users’ demerit was evaluated from the view point of 8 items: (1) price, (2) performance,
(3) product life, (4) amount used, (5) feeling of safety, (6) feeling of security, (7)
convenience, and (8) comfort. These evaluation results were summarized in Table 5.3. It
was particularly worth noting that organic model improved their performance and product
life.
Producers’ demerit
Producers’ demerit was evaluated from the view point of 8 items: (1) corporate image,
(2) environmental costs, (3) technological power, (4) intellectual property, (5) equipment
expenses, (6) equipment maintenance costs, (7) operation management costs, and (8)
operation safety. These evaluation results were summarized in Table 5.3. It was
particularly worth noting that organic model contributed producers by corporate image up
and intellectual properties.
Table 5.3 Socio-Economic Impact

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5.6 Experimental Section
Martial
Poly(decyl viologen)
4,4’-Bipyridine (320 mg) and 1,10-dibromodecan were dissolved in a methanol/DMF
mixture (0.9 ml) at 60˚C for overnight. The resulting precipitate was washed with acetonitrile,
then with chloroform, and dried under reduced pressure for 12 h. Poly(decyl viologen) was
obtained as a yellow solid (400 mg).
The molecular weight of the polymer was Mn = 6 000. Elemental analysis of PV10: C,
52.5; H, 6.4; and N, 6.1; Calcd. for C20H28N2Br2: requires C, 50.8; H, 6.4;and N, 5.9. The
PV10 was characterized by NMR spectroscopy. δH (500 MHz; D2O; Me4Si) 1.25 (12 H, t, J =
10.9 Hz, 2 × NCH2CH2C3H6), 1.98 (4 H, t, J = 13.3 Hz, 2 × NCH2CH2C3H6), 4.62 (4 H, t, J =
14.2 Hz, 2 × NCH2CH2C3H6), 8.44 (4 H, d, J = 5.7 Hz, β-H of pyridinium CH), 9.01 (4 H, d,
J = 5.7 Hz, α-H of pyridinium, ); δC(500 MHz; D2O; Me4Si) 25.3, 28.1, 28.5, 30.7, 62.3,
127.6, 145.5, 150.0.
Poly(decyl viologen) and poly(styrene sulfonate) complex
The comples of PV10 with poly(styrene sulfonate) (PSS) was prepared by adding a 5wt%
aqueous solution of PSS (Mw = 75 000, 18% solution obtained from Aldrich) in to a 5wt%
aqueous solution of PV10 in a molar ratio of 2:1. The obtained precipitate was collected by
filtration and dried under reduced pressure for 12 h. Poly(decyl viologen) and poly(styrene
sulfonate) complex was obtained as a yellow solid (500 mg).
Electrode Preparation and Electrochemical Measurements
PV10-PSS complex was dissolved in a mixture of HCl, water and dioxane in a weight
ratio of 5:50:45. The solution was spin-coated on a current collector such as a glassy carbon
substrate, ITO glass substrate and ITO PET substrate, followed by drying at 80˚C for 24 hr
under vacuum, to yield the PV10-PSS film with a thickness of 50 ‒300 nm, respectively.
The electrochemical measurements were performed using a conventional three-electrode
cell under standard ambient condition. A normal potentiostat system (BAS Inc. ALS660B)
was used for the cyclic voltammetry, chronopotentiometry and other electrochemical
measurements. A coiled platinum wire and Ag/AgCl were used as the counter and reference
electrode. The cyclic voltammogram was measured in a 0.1 M NaCl aq. and its pH were
controlled adding HCl and NaOH.
The chronopotentiometry were measured in 0.1 M NaCl aq.. (1) Cycle performance test:
the PV10 half cell was charged and discharged at 60 C repeatedly until 100 cycles. (2)
Charging rate performance test: the PTVE half cell was charged at the 60‒1200 C-rate, and its

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discharging capacity was measured at 60 C. (3) Discharging rate performance test: the PTVE
half cell, fully charged at 60 C, was discharged at a 60‒1200 C-rate, and the discharging
capacities were measured.
Cell Fabrication and Battery Performance
A semi-organic test full-cell was fabricated using the PTAm cathode and a zinc anode in
the aqueous solution of 0.1 M ZnCl2 and 0.1M NH4Cl. The charging-discharging rate
performance was measured using chronopotentiometry at 60‒1200 C-rate. The cycle
performance of the cell was tasted by repeated charging-discharging galvanostatic cycles at 60
C. The cut-off potentials were 1.4 and 2.0 V vs. Zn/Zn2+. The impedance spectrum of
semi-organic model was measured with applied frequencies range of 0.1 to 2500 Hz.
An organic test full-cell was fabricated using the PTAm cathode and a viologen anode in
the aqueous solution of 0.1 M NaCl. The charging-discharging rate performance was
measured using chronopotentiometry at 60‒1200 C-rate.The cycle performance of the cell
was tasted by repeated charging-discharging galvanostatic cycles at 60 C. The cut-off
potentials were 0.8 and 1.6 V vs. violgen/viologen+. The impedance spectrum of organic
model was measured with applied frequencies range of 0.1 to 2500 Hz.
Other Measurements
The 1H- and 13C NMR spectra were recorded using a JEOL Lambda 500 or Bruker
AVANCE 600 spectrometer, and Gel permeation chromate graphy was performed with DMF
using a Tosoh HLC-8220 instrument. Electron spin resonance (ESR) spectra were obtained
using a JEOL JES-TE200ESR spectrometer with 100 kHz field modulation. The
magnetization and magnetic susceptibility of the powder polymer sample were measured by
Quantum Design MPMS-7SQUID (superconducting quantum interference device)
magnetometer. The magnetic susceptibility was measured from 10 to 300 K in a 1.0 T field.
The thermal analyses were performed with a Seiko DSC220C and a TG/DTA 220 thermal
analyzer at a heating rate of 10°C/min under helium.
References
[1] B. Scrosati, W. A. V. Schalkwijk, "Advances in Lithium-Ion Batteries", Plenum
Publishers, 2002.
[2] R. J. Brodd, K. R. Bullock, R. A. Leising, R. L. Middaugh, J. R. Miller, E. Takeuchi, J.
Electrochem. Soc. 2004, 151, K1.
[3] G. Pistoia, "Batteries For Portable Devices ", Elsevier Amsterdam, 2005.
[4] J. Y. G. I. Likhtenshtein, S. Nakatsuji, A. I. Sminov and, R. Tamura, "Nitroxides",
Wiley-VCH, Weinheim, 2008.

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[5] W. A. Walter, "The chemistry of Free Radicals", Oxford University Press, London, 1948.
[6] H. Nishide, S. Iwasa, Y. J. Pu, T. Suga, K. Nakahara, M. Satoh, Electrochim. Acta 2004,
827.
[7] H. Nishide, T. Suga, Electrochem. Soc. Interface 2005, 14, 32.
[8] T. Suga, H. Konishi, H. Nishide, Chem. Commun. 2007, 1730.
[9] T. Suga, Y. J. Pu, S. Kasatori, H. Nishide, Macromolecules 2007, 40, 3167.
[10] H. Nishide, K. Oyaizu, Science 2008, 319, 737.
[11] K. Oyaizu, Y. Ando, H. Konishi, H. Nishide, J. Am. Chem. Soc. 2008, 130, 14459.
[12] K. Oyaizu, T. Suga, K. Yoshimura, H. Nishide, Macromol. 2008, 41, 6646.
[13] K. Koshika, N. Sano, K. Oyaizu, H. Nishide, Chem. Commun. 2009, 836.
[14] K. Koshika, N. Sano, K. Oyaizu, H. Nishide, Macromol. Chem. Phys. 2009.
[15] K. Oyaizu, H. Nishide, Adv. Mater. 2009.
[16] T. Suga, H. Ohshiro, S. Sugita, K. Oyaizu, H. Nishide, Adv. Mater. 2009, 21, 1627.
[17] C. Iwakura, T. Kawai, M. Nojima, H. Yoneyama, Journal of the Electrochemical Society
1987, 134, 791.
[18] J. M. Zen, D. M. Tsai, H. H. Yang, Electroanalysis 2002, 14, 1597.

Page 96

Page 97
Chapter 6
Synthesis and Electrochemical Properties of TEMPO Substituted
Polyacrylamide
6.1 Introduction
6.2 Synthesis of the TEMPO Substituted Polyacrylamide
6.3 Electrochemical Properties of the TEMPO Substituted Polyacrylamide
6.4 Cathode Performance of the TEMPO Substituted Polyacrylamide
6.5 Battery Performance of the Organic Secondary Battery
6.6 Experimental Section
References

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6.1 Introduction
A combination of a radical polymer and aqueous electrolyte showed improved
charging-discharging rate performance over the combination of radical polymer and organic
electrolyte.[1-10]
Recently, we designed a hydrophilic radical polymer,
poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl vinylether) (PTVE), which sufficiently
functioned even in an aqueous electrolyte, and reported the following electrode performance
[11, 12]: (i) High charging and discharging capacity of 131 mAh g-1 ascribed to the
stoichiometric redox of the radical moieties, (ii) Long cycle life, often exceeding 1000 cycles,
derived from the chemical stability of the radicals and from the amorphous electrode structure,
and (iii) High charging-discharging rate performance (1200 C) resulting from the rapid
electron-transfer process of the radical moiety and the high equivalent electrical conductivity
of the aqueous electrolyte on the order of 10-2–10-3 m2 S mol-1, which is 10-times higher than
that of organic electrolytes.[13] (The rate of 1 C is defined as the current density at which the
charging or discharging of the cell takes 1h. Most conventional batteries function during the
charging or discharging at 1–2 C.)
However, thicken the film for earning capacity and improve the cycle performance were
remained as issues to be solved. We designed new hydrophilic radical polymer,
poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl acrylamide), which showed a high compatibility
for aqueous electrolyte and a low solubility for aqueous electrolyte. We selected
polyacrylamide as a polymer back bone of new hydrophilic polymer. Polyacrylamide has
found numerous applications as a soil conditioner, in wastewater treatment, in the cosmetic,
paper, and textile industries, and in the laboratory as a solid support for the separation of
proteins by electrophoresis.[14-19] Polyacrylamide is also known as water soluble polymer
derived from amide group with a high hydrophilic property.[20-22] Additionally polyacrylamide
with high molecular weight was easy to be obtained by radical polymerization.[23-25]
This molecular design was expected to improve the charging-discharging performance.
The increased amount of aqueous electrolyte within the polymer could contribute to rapid
charge propagation within the polymer, allowing quantitative charging-discharging capacity
with thicker films. On the other hand, increased molecular weight could stop to suppress the
low molecular weight polymer elution into electrolyte, leading degradation of electrode cycle
performance. In this chapter, author report a design for another hydrophilic radical polymer,
and its characterization and electrochemical properties. Additionally organic based secondary
battery was fabricated with PTAm cathode, PV10 anode and aqueous sodium chloride
solution.

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Synthesis and Electrochemical Properties of TEMPO Substituted Polyacrylamide
- 93 -
6.2 Synthesis of the TEMPO Substituted Polyacrylamide
6.2.1 Monomer Synthesis
2,2,6,6-Tetrametylpiperidine-4-yl acrylamide was prepared by aminolysis reaction of
acrylchloride and 4-amino-2,2,6,6-tetrametylpiperidine in toluene. The obtained monomer
was characterized by elemental analysis, FAB-MS and 1H- and 13C-NMR spectroscopes,
supporting the high purity.
Scheme 6.1 Monomer synthesis of PTAm.
6.2.2 Polymer Synthesis
Poly(2,2,6,6-tetrametylpiperidine-4-yl acrylamide) was prepared by radical
polymerization using 2,2’-Azobisisobutyronitile (AIBN) as an initiator. The molecular weight
of obtained polymer were 96 000. The obtained polymer was characterized by elemental
analysis and 1H- and 13C-NMR spectroscopes, supporting the fact that the radical
polymerization proceeded without any side reactions. The polymer was soluble in acetonitrile,
methanol and THF.
The polymer treated in m-chloroperbenzoic acid-THF solution for 3h. The resulting
polymer was precipitated into diethylether/hexane mixed solvent to remove the
m-Chloroperbenzoic acid and low molecular polymer. The polymer was soluble in acetonitrile,
methanol and THF, but insoluble in water. The obtained polymers were characterized by
elemental analysis and 1H- and 13C-NMR spectroscopes of the chemically reduced
(radical-quenched) polymers, supporting the oxidation of piperidine was proceed without any
side reactions.
.
Scheme 6.2 Synthesis procedure of PTAm.

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Chapter 6
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6.2.3 Unpaired Electron Concentration
The TEMPO radical moiety of PTVE was characterized with ESR spectroscopy and
SQUID magnetic measurement. The PTAm powder gave a single broad ESR at g = 2.0067
(Figure 6.1) corresponding to that of TEMPO (2.0056 [26]). The broadening of the ESR
spectrum is explained by intrachain dipole-dipole interaction due to the close distance among
the polymer-bound radical sites.
Figure 6.1 ESR spectrum of the powder sample of PTAm.
The unpaired electron density in PTAm was determined from the 1/χmol versus T plots
(Figure 1d), based on the Curie-Weiss rule according to 1/χpara = T/C - θ/C where C is a Curie
constant defined as Neg2μB
2S(S + 1)/(3kB). The slope of the 1 χmol versus T plots corresponded
to 1/C and gave an unpaired electron density of Ne = 1.95 × 1021 spin/g for PTAm The linear
relation was ascribed to a typical paramagneric behavior of the unpaired electrons of PTAm,
and its slope gave the unpaired electron or radical concentration of the PTAm sample, in the
example of Figure 6.2, of 0.96 per monomer unit of PTAm. A maximum effective
charging-discharging capacity per weight of 114 mAh g-1
was calculated using
formula-weight-based charging-discharging capacity 119 mAh g-1× 0.96. The unpaired
electron concentration almost maintained over three months under ambient conditions.
Figure 6.2 Plots of 1/magnetic susceptibility (15 mg) vs. temperature (Curie-Weiss plots) for the
powder sample of PTVE. Inset: ESR spectrum of the powder sample of PTVE.

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Synthesis and Electrochemical Properties of TEMPO Substituted Polyacrylamide
- 95 -
6.2.4 Thermal Properties and Hydrophilic Properties
Unpaired electron concentration in PTAm was maintained up to 150°C (Figure 6.3)
Thermal analysis revealed that PTAm itself was stable at 200°C: the 10% decomposition
temperature 276°C. Glass transition temperature (Tg) of PTAm was not find from 0―150°C,
which was acceptable because other polyacrylamide such as 165°C[27] of poly(acrylamide)
and 180°C[27] of poly(N-methyl-N-phenylacrylamide). This glass transition temperature
elevation could be derived from hydrogen bonding in the acrylamide group.
Figure 6.3 Relative concentration of unpaired electrons (●) and relative weight (—) of the powder
sample of PTVE. Inset: DSC thermogram.
The hydrophilic property of the PTVE layer was examined by contact angle measurement
of a water droplet on the surface of PTVE layer (The surface formed by spin-coating was
smooth with a roughness of ± 4 nm on an AFM image). The contact angle was 63–69°, which
was significantly smaller than 82–89° for the surface of the lipophilic polymethacylate-based
TEMPO Polymer (PTMA), and supported the hydrophilicity of the PTVE polymer. The
volume swell ratio of the PTVE layer (thickness of 1.1 μm) was estimated by microscopic
analysis of the polymer volume before and after swelling in water. The degree of swelling
under equilibrated conditions was ca. 1.4 (v/v), which indicated that the polymer had a
sufficient water absorbability for functioning as an electrode-active material in aqueous
electrolytes.
6.3 Electrochemical Properties of the TEMPO Substituted Polyacrylamide
6.3.1 Redox Properties
The cyclic voltammogram of the PTAm film repeatedly displayed a chemically reversible
redox wave at -0.63 vs. (Ag/AgCl) in a 0.1 M NaBF4 aq. at pH 6.8 (Figure 6.4 (a)). The
anodic or oxidation peak was sharper than the cathodic or reduction peak, although the
oxidation and reduction capacities or the peak areas almost coincided with each other. The
peak separations of PTAm film were very narrow, which gave the value of 6, 30, 51 and 80

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Chapter 6
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mV with sweep rates of 1, 5, 10 and 20 mV/s, respectively. This result indicated rapid charge
propagation within the polymer film.
Figure 6.4 (a) Cyclic voltammograms of the PTAm film in 0.1 M NaBF4 aq. with sweep rates of 1, 5,
10 and 20 mV/s. (b) Redox couple of PTAm.
In neutrality and also acidic condition with pH 1–8, PTAm demonstrated stable redox
ability and obtained almost quantitative redox capacity respectively (inset of Figure 6.5). On
the other hand, in basic condition with pH of more than 9, PTAm demonstrated redox wave
attenuation with a voltage sweep and, because oxoammonium cation generated by oxidation
of nitroxide radical changed to an electrochemically inert species by addition reaction with
hydroxide ion in electrolyte.
Figure 6.5 Relative redox capacity of PTAm on pH. Inset: Cyclic voltammograms of pH 1, 7 and 12
6.3.2 Thickness Dependency
The redox capacity was proportional to the film thickness and reached 51 mC cm-2 for the
film with a thickness of 1.2 μm, even in the absence of conductive additives which are
frequently employed in battery electrodes (Figure 6.6). These results mean that the PTAm
polymer was homogeneously solvated with aqueous electrolyte phase to compensate the

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Synthesis and Electrochemical Properties of TEMPO Substituted Polyacrylamide
- 97 -
charge, and that the TEMPO group of the PTAm worked as the redox site. These results also
suggested that the polymer film fabricated by the solution-based, e.g., spin-coating, process
did not involve any structural defects to decrease the capacity and to prevent the charge
transfer within the polymer.
Figure 6.6 Redox capacity per area for the PTVE film with the thickness of 35 nm–1.2 μm. The solid
line represents the calculated redox capacity with the coating amount.
6.4 Cathode Performance of the TEMPO Substituted Polyacrylamide
6.4.1 Charging-discharging Performance
The charging-discharging curves of the half cell exhibited a plateau voltage at 0.66–0.71
V vs. Ag/AgCl (Figure 6.7), which agreed with the redox potential of the PTAm film (0.68 V)
shown in Figure 6.4. The charging-discharging capacity almost coincided with each other at
ca. 114 mAh g-1 and agreed with the calculated capacity obtained in the Figure. 6.6 (4.1 mC
cm-2 × 100 nm thickness).
Figure 6.7 Charging–discharging curve of the PTAm film at charging-discharging rate of 60 C.

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Chapter 6
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6.4.2 Charging-discharging Rate Performance
The PTAm half-cell using 0.1 M NaBF4 aq. was charged at a 60–1800 C-rate and then
discharged at 60 C to examine the charging rate performance (Figure 6.8 (a)). The coulombic
efficiency (discharging capacity over the charging capacity) was maintained at almost 100%
from 60 to 1800 C. This result means that the charging rate performance was able to be
evaluated with charging capacity. The charging capacity gradually decreased to 90% of the
initial capacity at 1200 C (Inset of Figure 6.8 (a)). This rapid charging was derived from the
combination of hydrophilic radical polymer and aqueous electrolyte.
Figure 6.8 (a) Charging curves and (b) Discharging curves of the half-cell of PTAm film in 0.1 M
NaBF4 aq. with C-rate of 60–600. Inset of (a): Charging rate performance and (b): discharging rate
performance at 60–1800 C.
On the other hand, to examine the discharging rate performance, the fully charged PTAm
half-cell was discharged at a 60–1800 C-rate (Figure 6.8 (b)). The discharging capacity
gradually decreased to 80% of the initial capacity at 1200 C (Inset of Figure 6.8 (b)). This
result indicated that the rate-determining process in electrode reaction was discharging
process.
6.4.3 Charging-discharging Cycle Performance
The cycle performance of the charging-discharging at the cut-off voltages of 0.4–0.9 V and
C-rate of 60 C is shown in Figure 6.8. The coulombic efficiency, i.e., discharging capacity vs.
charging capacity, is maintained at almost 100% even after 10000 charging-discharging
cycles, indicating that the charged species, the oxoammonium form of PTVE,
stoichiometrically contributed to the following discharging process. The discharging capacity
was maintained to ca. 85% of the initial value after 10000 cycles, suggesting no partial elution
out of the PTAm polymer into the electrolyte.

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Synthesis and Electrochemical Properties of TEMPO Substituted Polyacrylamide
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Figure 6.9
Discharging capacity for the half-cell composed of the PTAm film on the
charging-discharging cycle number at the charging–discharging rate of 60 C. Inset:
Charging-discharging curve of the PTAm film.
6.5 Battery Performance of the Organic Secondary Battery
6.5.1 Semi-Organic Secondary Battery Using Zinc Anode
A test full-cell was fabricated using the PTAm cathode and a zinc anode in the aqueous
solution of 0.1 M ZnCl2 and 0.1M NH4Cl. The charging-discharging curves for the fabricated
cell displayed a plateau voltage at 1.68 V (vs. Zn/Zn2+) with the charging capacity of 112
mAh g-1 and the discharging capacity of 98 mAh g-1 (Figure 6.10 (a)). The cycle performance
of the charging-discharging at the cut-off voltages of 1.5–1.9 V and C-rate of 60 C is shown in
the Figure 6.10 (b). The columbic efficiency is maintained at almost 85% even after 100
charging-discharging cycles. The discharging capacity gradually decreases to ca. 75% of the
initial after 100 cycles. These results supported the potential of the aqueous electrolyte-based
organic radical polymer battery.
Figure 6.10 (a)Charging–discharging curve of the test cell fabricated with PTAm cathode, zinc
anode, aqueous solution of 0.1 M ZnCl2 and 0.1M NH4Cl. (b) coulombic efficiency (●) and discharging
capacity (○) on the cycle.

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Chapter 6
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6.5.2 Organic Secondary Battery Using PV10 Anode
A organic model test full-cell was fabricated using the PTVE cathode and a PV10 anode
in the aqueous solution of 0.1 M NaBF4. The charging-discharging curves for the fabricated
cell displayed a plateau voltage at 1.18 V (vs. PV10/PV10+) with the capacity of ca. 100 mAh
g-1 (Figure 6.11 (a)), which almost coincide with formula weight based capacity. The charging
capacity and the discharging capacity was agreed each other, indicating improvement of
coulombic efficiency comparing semi-organic model. The cycle performance of the
charging-discharging at the cut-off voltages of 1.1–1.5 V and C-rate of 60 C is shown in the
inset of Figure 6.11 (b). The columbic efficiency is maintained at almost 100% even after
1000 charging-discharging cycles. The discharging capacity gradually decreases to ca. 85% of
the initial after 1000 cycles. These results supported the potential of the aqueous
electrolyte-based organic radical polymer battery.
Figure 6.11 (a) Charging–discharging curve of the test cell fabricated with PTAm cathode, PV10
anode, aqueous solution of 0.1 M NaCl. (b) discharging capacity on the cycle.
In summary, PTAm was synthesized as an electrode-active and hydrophilic radical
polymer. The PTAm film displayed chemically reversible redox wave in aqueous electrolyte.
PTVE with even film thickness of 1.2 μm gave redox capacity in agreement with that
calculated with the film thickness, suggesting that PTAm film was defect-free and
homogeneously solvated with aqueous electrolyte. The PTAm film demonstrated rapid
charging-discharging performance based on virtue of the combination of the hydrophilic
radical polymer and the aqueous electrolyte possessing a high electrical conductivity. The
fabricated cell composed of this polymer cathode, PV10 anode and aqueous electrolyte
showed 1.2 V of output voltage, stable charging-discharging curves and cycle performance
exceeding 1000 cycles. Application of hydrophilic radical polymer for cathode active material
in aqueous electrolyte-type organic secondary battery was demonstrated.

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Synthesis and Electrochemical Properties of TEMPO Substituted Polyacrylamide
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6.6 Experimental Section
Martial
Preparation of 2,2,6,6-tetrametylpiperidine-4-yl acrylamide
Acryl chloride (1.3 ml) was added dropwise to ice-cold solution of
4-amino-2,2,6,6-tetrametylpiperidine (2.8 ml) in anhydrous benzene (60 ml) and triethyl
amine (0.9 ml) under an argon atmosphere with magnetic stirring. The mixture was
vigorously stirred for 1 h at 5˚C and then additionally for 1 h at room temperature. At the end
of the reaction, the precipitate was collected by filtration, extracted with dichloromethane and
washed with K2CO3 aq. The solvent was removed in vacuo, and the residue was purified
using a silica gel column with ethyl acetate. Appropriate fraction was collected and
crystallized from ethanol/hexane mixed solution. The acrylamide monomer was isolated as a
white crystal (1.1 g).
The elemental analysis: C, 68.7; H, 10.7; and N, 13.2; Calcd. for C11H20NO2: requires C,
68.5; H, 10.5;and N, 13.3. δH (500 MHz; CDCl3; Me4Si) 6.28 (1H, d, J = 1.5 Hz, vinyl CH2),
6.06 (1H, q, J = 10.4 Hz, vinyl CH), 5.63 (1H, dd, J = 1.5 Hz, vinyl CH2), 5.29 (1H, s, amide
NH), 4.35 (1H, d, J = 12.2 Hz, piperidine CH), 1.94 (2H, dd, J = 4.0 Hz, piperidine CH2),
1.27 (6 H, s, 2 × CH3), 1.13 (6 H, s, 2 × CH3) 0.94 (2H, t, J = 12.2 Hz, piperidine CH2);
δC(500 MHz; CDCl3; Me4Si) 28.5, 34.9, 42.7, 45.2, 51.1, 126.4, 131.0, 164.8. Mass: m/z,
211.2 (found), 210.3 (calcd).
Radical polymerization of the acrylamide monomer
2,2,6,6-tetrametylpiperidine-4-yl acrylamide (320 mg) was dissolved in a methanol (0.9
ml). 2,2’-Azobisisobutyronitile (AIBN) (4.9 mg) was added to the solution. The glass
ampoule containing the solution was sealed. Then the solution was heated for 3 h at 85˚C. The
resulting solution was evaporated, and dissolved in small amount of chloroform. The solution
was added dropwise to chloroform/hexane (1/4 v/v 100 ml). The precipitate was collected by
filtration, and dried under reduced pressure for 12 h. poly(2,2,6,6-tetrametylpiperidine-4-yl
acrylamide) was obtained as a white powder (220 mg).
The molecular weight of the polymer was Mn=87 000. Elemental analysis of
poly(2,2,6,6-tetrametylpiperidine-4-yl acrylamide): C, 68.1; H, 10.9; and N, 13.19; Calcd. for
C11H20NO2: requires C, 68.5; H, 10.5 and N, 13.3. The precursor polymer was characterized
by NMR spectroscopy. δH (500 MHz; CDCl3; Me4Si) 6.28 (1 H, br s, amide NH), 4.20 (1 H,
m, piperidine CH), 2.21 (1 H, br s, alkyl CH2), 1.85 (2 H, br s, piperidine CH2), 1.66 (1 H, br
s, alkyl CH2), 1.25 (6 H, s, 2 × CH3), 1.12 (6 H, s, 2 × CH3), 1.00 (2 H, br s, piperidine CH2),
0.65 (1 H, br s, alkyl CH2); δC(500 MHz; CDCl3; Me4Si) 28.7, 29.0, 35.1, 42.3, 42.7, 45.2,
51.0, 174.4.

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Oxidation of poly(2,2,6,6-tetrametylpiperidine-4-yl acrylamide)
poly(2,2,6,6-tetrametylpiperidine-4-yl acrylamide) (150 mg) was added to ice-cold
solution of m-chloroperbenzoic acid (620 mg) in THF (5 ml), and stirred for 3 h at room
temperature. The polymer was solved in THF with oxidation progress.The solution was added
dropwise to diethylether/hexane (1/1 v/v 200 ml). The precipitate was collected by filtration,
and dried under reduced pressure for 12 h. poly(2,2,6,6-tetrametylpiperidinyloxy-4-yl
acrylamide) was obtained as an orange powder (140 mg). The molecular weight of the
polymer was Mn=90 000 with a dispersity of Mw/Mn =3.0.
Characterization of the radical polymer
PTAm was characterized by the g-value (2.0067) of the ESR signal to contain the
TEMPO moiety. The radical concentration or the concentration of the unpaired electron of
each sample was determined on the basis of the assumption of being paramagnetic at room
temperature by integration of the ESR signal standardized with that of the TEMPO solution.
The radical concentration was also analyzed by the slope of the Curie plots and the saturated
magnetization in the SQUID measurement. These radical concentration values estimated by
the two methods almost agreed with each other.
Electrode Preparation and Electrochemical Measurements
The THF solutions of PTAm (10–55 g/L) were spin-coated on a current collector such as
a glassy carbon substrate, followed by drying at 70˚C for 4 hr under vacuum, to yield the
PTVE film with a thickness of 50 nm–1.2 μm, respectively.
The electrochemical measurements were performed using a conventional three-electrode
cell under standard ambient condition. A normal potentiostat system (BAS Inc. ALS660B)
was used for the cyclic voltammetry, chronopotentiometry and other electrochemical
measurements. A coiled platinum wire and Ag/AgCl were used as the counter and reference
electrode. The cyclic voltammogram was measured in a 0.1 M NaCl aq. and NaBF4 aq..
The chronopotentiometry were measured in 0.1 M NaCl aq., (1) Cycle performance test:
the PTAm half cell was charged and discharged at 60 C repeatedly until 1000 cycles. (2)
Charging rate performance test: the PTAm half cell was charged at the 60–1800 C-rate, and its
(discharging) capacity was measured (at 60 C). (3) Discharging rate performance test: the
PTAm half cell with fully charged at 60 C was discharged at 60-1800 C-rate, and their
discharging capacities were measured.
Cell Fabrication and Battery Performance
A semi-organic test full-cell was fabricated using the PTAm cathode and a zinc anode in
the aqueous solution of 0.1 M ZnCl2 and 0.1M NH4Cl. The cycle performance of the cell was

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Synthesis and Electrochemical Properties of TEMPO Substituted Polyacrylamide
- 103 -
tasted by repeated charging-discharging galvanostatic cycles at 60 C. The cut-off potentials
were 1.5 and 1.9 V vs. Zn/Zn2+. An organic test full-cell was fabricated using the PTAm
cathode and a viologen anode in the aqueous solution of 0.1 M NaCl. The cycle performance
of the cell was tasted by repeated charging-discharging galvanostatic cycles at 60 C. The
cut-off potentials were 1.1 and 1.5 V vs. violgen/viologen+.
Other Measurements
The 1H- and 13C NMR spectra were recorded using a JEOL Lambda 500 or Bruker
AVANCE 600 spectrometer, and Gel permeation chromate graphy was performed with DMF
using a Tosoh HLC-8220 instrument. Electron spin resonance (ESR) spectra were obtained
using a JEOL JES-TE200ESR spectrometer with 100 kHz field modulation. The
magnetization and magnetic susceptibility of the powder polymer sample were measured by
Quantum Design MPMS-7SQUID (superconducting quantum interference device)
magnetometer. The magnetic susceptibility was measured from 10 to 300 K in a 1.0 T field.
The thermal analyses were performed with a Seiko DSC220C and a TG/DTA 220 thermal
analyzer at a heating rate of 10°C/min under helium.
Referenece
[1] H. Nishide, S. Iwasa, Y. J. Pu, T. Suga, K. Nakahara, M. Satoh, Electrochim. Acta 2004,
827.
[2] T. Suga, Y. J. Pu, K. Oyaizu, H. Nishide, Bulletin of the Chemical Society of Japan 2004,
77, 2203.
[3] H. Nishide, T. Suga, Electrochem. Soc. Interface 2005, 14, 32.
[4] T. Suga, H. Konishi, H. Nishide, Chem. Commun. 2007, 1730.
[5] T. Suga, Y. J. Pu, S. Kasatori, H. Nishide, Macromol. 2007, 40, 3167.
[6] H. Nishide, K. Oyaizu, Science 2008, 319, 737.
[7] K. Oyaizu, Y. Ando, H. Konishi, H. Nishide, J. Am. Chem. Soc. 2008, 130, 14459.
[8] K. Oyaizu, T. Suga, K. Yoshimura, H. Nishide, Macromol. 2008, 41, 6646.
[9] K. Oyaizu, H. Nishide, Adv. Mater. 2009.
[10] T. Suga, H. Ohshiro, S. Sugita, K. Oyaizu, H. Nishide, Adv. Mater. 2009, 21, 1627.
[11] K. Koshika, N. Sano, K. Oyaizu, H. Nishide, Chem. Commun. 2009, 836.
[12] K. Koshika, N. Sano, K. Oyaizu, H. Nishide, Macromol. Chem. Phys. 2009.
[13] D. R. Lide, in Handbook of Chemistry and Physics, 72nd edition, CRC Press, Boston,
1991, p. 96.
[14] F. A. Andersen, International Journal of Toxicology 2005, 24, 21.
[15] M. Friedman, Journal of Agricultural and Food Chemistry 2003, 51, 4504.
[16] A. Jungbauer, R. Hahn, Journal of Chromatography A 2008, 1184, 62.

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[17] N. C. Stellwagen, E. Stellwagen, Journal of Chromatography A 2009, 1216, 1917.
[18] J. R. Stokes, L. J. W. Graham, N. J. Lawson, D. V. Boger, Journal of Fluid Mechanics
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[19] G. R. Warnick, J. R. McNamara, C. N. Boggess, F. Clendenen, P. T. Williams, C. C.
Landolt, Clinics in Laboratory Medicine 2006, 26, 803.
[20] J. Barton, S. Kawamoto, K. Fujimoto, H. Kawaguchi, I. Capek, Polymer International
2000, 49, 358.
[21] S. Guha, B. Ray, B. M. Mandal, Journal of Polymer Science Part a-Polymer Chemistry
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[22] R. K. Wanchoo, P. K. Sharma, European Polymer Journal 2003, 39, 1481.
[23] M. Albarghouthi, B. A. Buchholz, E. A. S. Doherty, F. M. Bogdan, H. H. Zhou, A. E.
Barron, Electrophoresis 2001, 22, 737.
[24] S. Durmaz, O. Okay, Polymer 2000, 41, 3693.
[25] D. Q. Xiao, M. J. Wirth, Macromolecules 2002, 35, 2919.
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Wiley-Interscience Publication, Weinheim, 1989, p. 217.

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Chapter 7
Conclusion and Future Prospects
7.1. Conclusion
7.2. Future Prospects
References

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- 106 -
7.1 Conclusion
In this thesis, the author described the design and synthesis of a series of hydrophilic
radical polymers and their application to energy storage device. In this chapter, the
characteristics of aqueous electrolyte-type radical polymer battery and important conclusions
derived from this study are summarized.
In chapter 1, the author summarized ‘current situations and issues of secondary batteries’,
‘the twelve principals of green chemistry and practice in design of organic secondary battery’
and ‘radical polymers for electrode-active materials’, respectively.
In chapter 2, the synthesis and electrochemical property of TEMPO substituted
polyvinylether were described. The TEMPO substituted polyvinylether,
poly(2,2,6,6-Tetrametylpiperidne-N-oxyl-4-vinyl ether) was designed as a hydrophilic and
electrode-active radical polymer with maximum effective capacity of 135 mAh g-1. The
TEMPO substituted polyvinylether was synthesized by cationic radical polymerization with
high yield. The TEMPO substituted polyvinylether film coated on a glassy carbon substrate
showed chemically reversible redox with 1μm film thickness in aqueous electrolyte. The
obtained redox capacity was agreed with calculated capacity. This result suggested that the
TEMPO substituted polyvinylether film was homogeneously solvated with the aqueous
electrolyte phase to compensate for the charge and that almost all of the TEMPO moiety of
the polymer functioned as the redox site. The charging-discharging performance of the
TEMPO substituted polyvinylether film was highly stable, remaining more than 75% of the
initial capacity after 1000 cycles. The charging rate performance was also high, which showed
a rapid full charging within 3seconds. In comparing in organic electrolyte, only 30% of the
capacity was charged with 3seconds. This result means a combination of hydrophilic radical
polymer and aqueous electrolyte was effective to demonstrate a rapid charging.
In chapter 3, Affection of electrolyte conditions such as pH, salt concentration and salt
species for redox property of the TEMPO substituted polyvinylether was studied to fabricate a
test full-cell using zinc anode. The TEMPO substituted polyvinylether showed stable redox
ability in acidic and neutral pH conditions. The redox potential of the polymer fell with
decreasing salt concentration with a slope of 59 mV, indicating that the counter ions strongly
effect on the redox property. The charge transportation resistance within the polymer
decreased with the order of ion size, Cl-, BF4
-, and PF6
-, which agreed with the
charging-discharging rate performance in NaCl, NaBF4 and NaPF6 aq. This result indicated
that electrolyte condition affected on the charging-discharging performance. A test full-cell
was designed based on the results. The test cell was fabricated with a TEMPO substituted
polyvinylether cathode, zinc anode, and 0.1 M NH4Cl and ZnCl2 aqueous solutions,
demonstrating 1.7 of output voltage and more than 500 times rechargeability. This was the

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Conclusion and Future Prospects
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first report of an aqueous electrolyte-type radical polymer battery.
In chapter 4, health safety and disaster safety of radical polymers were assessed for
electrode application. For health safety, radical polymers were considered basically to be
non-toxic and low potential risks causing health hazards during the use and disposal. Radical
polymers had a low bioavailability as well as most of general polymers. The polymers were
nonvolatile and insoluble for general solvents except for a few kinds of organic solvents such
as acetonitrile, DMSO. i.e. the polymers had low possibility to enter the human body through
the respiratory tract and skin. On the other hand, for disaster safety, radical polymers were
considered basically to be low potential risks causing disaster hazards. Radical polymers were
chemically stable, no explodability, flammability and pyrophoric property. The polymers had
a low reactivity toward oxygen and water, remaining unchanged with no decomposition and
deactivation under ambient conditions over 1 year. The polymers were also thermally stable.
Their10% decomposed temperatures are higher than 200°C. This was sufficiently higher than
envisioned operating temperature of the battery.
In chapter 5, the battery design and performance of the aqueous electrolyte-type radical
polymer battery were studied for totally organic model. Polydecilviologen was selected as a
hydrophilic electrode-active polymer for totally organic model which was expected to show
1.3 V of output voltage. The polydecilviologen was synthesized by Menschutkin reaction of
4,4’-bipiridyle and 1,10-dibromodecane. The totally organic test full-cell was fabricated with
a TEMPO substituted polyvinylether cathode, polydecilviologen anode and 0.1 M NaCl
aqueous electrolyte. The organic model cell demonstrated 1.3 V of output voltage and more
than 1000 cycle rechargeability. In addition, the green characteristics of this model were also
evaluated comparing with semi-organic model, which was composed of zinc and aqueous zinc
chloride solution, by i-Messe, an evaluation method proposed by the Green Sustainable
Chemistry Network.
In chapter 6, synthesis and electrochemical property of TEMPO substituted
polyacrylamide were studied for new hydrophilic radical polymer. TEMPO substituted
polyacrylamide, poly(2,2,6,6-Tetrametylpiperidne-N-oxyl-4yl-acrylamide) was synthesized
by radical polymerization with high molecular weight. This polymer showed 2times higher
volume swell rate for water than that of TEMPO substituted polyvinylether. The TEMPO
substituted polyacrylamide film coated on glassy carbon substrate showed chemically
reversible redox ability. The charging-discharging cycle performance was also high,
remaining more than 85% of the initial capacity after 10000 cycles. This result suggested that
the long cycle life was derived from no partial elution of the TEMPO substituted
polyacrylamide.

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Chapter 7
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7.2 Future Perspective
Research and study on functional polymers will continue to expand because of no
limitation of their molecular design. Many issues which are difficult to solve by inorganic
materials will be solved by new molecular design. The organic secondary battery using radical
polymer also will be improved and demonstrate the higher performance by new molecular
design. In this section the author proposes improvement polymer design for anode polymer
and additionally suggest another application using TEMPO substituted radical polymer.
7.2.1 High Performance Hydrophilic Radical Polymer Anode
The author proposes a molecular design for hydrophilic and anode-active polymer for
TEMPO substituted polymer cathode. In chapter 5 and 6, PV10-PSS was synthesized and
applied for the organic secondary battery as an anode-active polymer. Viologen has been
studied as electrochromic materials [1-4] and also has several advantages as one of the energy
storage materials utilizing with TEMPO substituted polymers as follows: (i) chemically stable
in ambient condition and easily deal with them, (ii) suitable redox potential (1.0–1.2 vs.
TEMPO/TEMPO+) which less than the voltage of water electrolysis, and (iii) stable in wide
range of acidic and basic condition with pH 3–11. The viologen will showed improved
electrode performance by compact molecular design (Figure 7.1 (a)). The
poly(tripyridiniomesitylene) was expected to demonstrate (i) a high capacity (229 mAh/g), (ii)
improved charging-discharging rate performance derived from shortened distance between
redox units, and (iii) long cycle life derived from the suppression of polymer elution in
electrolyte by cross linked structure. The cross linked structure is synthesized by
electropolymerization, saving the process of solubility control for applying solvent and wet
process application (Figure 7.1 (b)).
Figure 7.1 (a) Molecular design for anode-active polymer and (b) scheme of electropolymerization.

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Conclusion and Future Prospects
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7.2.2 Wettability Control by Redox ability of Radical Polymers
A study on wettability control using temperature responsive polymer has paid much
attention, applying for cell growth medium.[5-7] Some acrylamide polymers such as
poly(N-isopropylacrylamide) (PNIPPAm)[8, 9] have a Lower Critical Solution Temperature
behavior, controlling their hydrophilic properties temperature. On the other hand, the PTAm
have a possibility to control its wettability using the redox property. The PTAm has a redox
couple between nitroxide radical and oxoammonium cation. The oxoammonium cation
showed a higher hydrophilicity derived from its higher polarity. The wettability of PTAm
applied to current collector was switched by electrochemical oxidation and reduction (Figure
7.2).
Figure 7.2 Wettability control using electrochemical oxidation and reduction.
References
[1] J. Volke, V. Volkeova, Chemicke Listy 1996, 90, 137.
[2] K. S. Schanze, T. S. Bergstedt, B. T. Hauser, C. S. P. Cavalaheiro, Langmuir 2000, 16,
795.
[3] R. J. Mortimer, A. L. Dyer, J. R. Reynolds, Displays 2006, 27, 2.
[4] K. Kamata, T. Kawai, T. Iyoda, Langmuir 2001, 17, 155.
[5] M. Yektafard, A. B. Ponter, Journal of Adhesion Science and Technology 1992, 6, 253.
[6] C. M. Chan, T. M. Ko, H. Hiraoka, Surface Science Reports 1996, 24, 3.
[7] Y. Shirai, K. Kawatsura, N. Tsubokawa, Progress in Organic Coatings 1999, 36, 217.
[8] H. G. Schild, Progress in Polymer Science 1992, 17, 163.
[9] S. H. Gehrke, Advances in Polymer Science 1993, 110, 81.

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Page 117
List of Publications
1. Kenichiroh Koshika, Naoki Sano, Kenichi Oyaizu, Hiroyuki Nishide, “An Ultrafast
Chargeable Polymer Electrode Based on the Combination of Nitroxide Radical and
Aqueous Electrolyte” Chemical Communications, 7, 836-838 (2009).
2. Hiroyuki Nishide, Kenichiroh Koshika, Kenichi Oyaizu, “An Environmentally Benign
Battery Based on Organic Radical Polymers” Pure and Applied Chemistry, (2009) in
press.
3. Kenichiroh Koshika, Naoki Sano, Kenichi Oyaizu, Hiroyuki Nishide, “An Aqueous
Electrolyte-Type Organic Secondary Battery Using Hydrophilic Radical Polymer
Cathode” Macromolecular Chemistry and Physics, (2009), submitted.
4. Kenichiroh Koshika, Masao Kitajima, Kenichi Oyaizu, Hiroyuki Nishide, “A
Rechargeable Battery Based on Hydrophilic Radical Polymer-Electrode and its Green
Assessment” Green Chemistry Letters and Reviews, (2009) in press.
5. Kenichiroh Koshika, Naoki Sano, Masao Kitajima, Kenichi Oyaizu, Hiroyuki Nishide, “A
Rechargeable Device Composed of Polymer Electrodes and Aqueous Electrolyte” Journal
of Green Chemistry, (2009), submitted.
6. Kenichiroh Koshika, Natsuru Chikushi, Naoki Sano, Kenichi Oyaizu, Hiroyuki Nishide,
“A Long Life Organic Electrode Based on TEMPO Substituted Polyacrylamid” Journal of
Materials Chemistry, (2009), submitted.
7. Takashi Kurata, Kenichiroh Koshika, Fumiaki Kato, Junji Kido, Hiroyuki Nishide, “An
Unpaired Electron-Based Hole-Transporting Molecule: Triarylamine-Combined Nitroxide
Radicals” Chemical Communications, 28, 2986-2988 (2007)

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Acknowledgements
The present thesis is the collection of the studies which have been carried out under the
direction of Prof. Dr. Hiroyuki Nishide, Department of Applied Chemistry in Waseda
University, during the 2007-2009. The author expresses the greatest acknowledgement to Prof.
Dr. Hiroyuki Nishide for his invaluable suggestion, discussion, and continuous
encouragement throughout this work.
The author also expresses his sincere gratitude to Prof. Dr. Shinji Takeoka and Assoc. Prof.
Dr. Kenichi Oyaizu (Waseda Univ.) for their valuable advice and encouragement. The
author wishes to thank Prof. Dr. Takayuki Homma (Waseda Univ.) for their efforts as
members on judging committee for the doctoral thesis.
The author appreciates Dr. Masao Kitajima (Waseda Univ.) for his valuable technical
advice and fruitful discussion on the GSC evaluation.
The author expresses the great acknowledgement to Dr. Yong-Jin Pu (Yamagata Univ.), Dr.
Takashi Kurata (Mitsubishi Chemical Co.), Dr. Takeo Suga (Waseda Univ.) from their
excellent advice, fruitful discussion, and encouragement through the experiments. Also
Acknowledgements are Dr. Kei Saito (Monash Univ.) Dr. Hidenori Murata (Nissan Co.), Dr.
Yosuke Okamura (Waseda Univ.), Dr. Yasunori Yonekuta (Fuji Film Co.), Dr. Takahiro Tago
(Asahi Kasei Co.), Dr. Hyundae Hah (Samsung Co.), Dr. Tsuyoshi Hyakutake (PWRI), and Dr.
Masami Shouji (Asahi Kasei Co.) for their constructive comments and discussion.
The author expresses the special thanks to all active and energetic collaborators, Mr.
Naoki Sano, Mr. Natsuru Chikushi, Mr. Wataru Tomita, and Mr. Hiroshi Yamada for their
strong assistance in the experimental work.
The author deeply thanks Mr. Takeshi Ibe, Mr. Fumiaki Katoh, Mr. Teruyuki Okayasu, Mr.
Satoshi Nakajima, Mr. Wihatmoko Waskitaji, Ms. Xiuli Zhuang, Mr. Won-Song Choi, and all
members in the laboratory for their fruitful discussion and kind assistance.
Finally, the author expresses his deepest gratitude heartily to his parents, Mr. Masao
Koshika, Mrs. Mizuho Koshika, and his brother, Mr. Jiroh Koshika, for their heartfelt
supports.
July, 2009
Kenichiroh Koshika