BIOPOLYMER-BASED RECHARGEABLE BATTERYamgs.or.kr/New/common/journal/vol6/vol6_no.2-10.pdf · A...

APEC Youth Scientist Journal Vol. 6 / No.2

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BIOPOLYMER-BASED RECHARGEABLE BATTERY

∗ LO Chun Kit Jason, WONG Chi Sum

1

1 The Chinese Foundation Secondary School, 8 Armony Road, Siu Sai Wan, HONG KONG

1. INTRODUCTION

A rechargeable battery is a type of secondary dry cell because its electrochemical

reactions are electrically reversible. Several different combinations of chemicals are

commonly used, including: lead–acid, nickel cadmium (NiCd), nickel metal hydride (NiMH),

lithium ion (Li-ion), and lithium ion polymer (Li-ion polymer). While lithium batteries are

widely used in different areas and extensively studied nowadays, they were first proposed in

the 1970s. Primary lithium batteries in which the negative electrode is made from lithium

pose safety issues. Soon, lithium-ion batteries were developed using material containing

lithium ions in both electrodes. The modern design of lithium-ion batteries advances to

incorporate the nanotechnology on the synthesis of lithium compound, so as to increase the

performance of the battery. As of 2011, lithium-ion batteries contribute for 66% (1,218,342

out of 1,847,264) of all portable secondary sales in Japan.

However, the improper disposal of rechargeable battery may raise environmental

issues as most of the materials used in the rechargeable battery are non-renewable and non-

biodegradable. These materials and organic solvents may also be toxic. For example,

cadmium may cause damage to soil micro-organisms and affect the breakdown of organic

matter. Moreover, lithium-ion batteries can be easily ignited. When they are burned, the

mercury in it will vaporize into the air and the lead inside will still exist in the ash. These may

end up polluting our water sources. Therefore, development of rechargeable battery using

renewable, biomaterials is an unarguable topic in scientific research.

∗ Correspondence to : LO Chun Kit Jason ([email protected])

APEC Youth Scientist Journal Vol.6 / No.2

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A polymer lithium ion rechargeable battery was first proposed and has been

available since 1995. The primary difference between polymeric lithium ion rechargeable

battery and new design is that the lithium-salt electrolyte is not held in an organic solvent but

in solid polymer composite such as polyethylene oxide and polyacrylnitrile. The advantage of

polymeric design is a potentially lower cost of manufacture. Therefore, studies of solid

polymer electrolyte have attracted world-wide interest.

Using conductive polymers in the fabrication of adaptable energy storage devices is

particularly interesting because of their fast redox switching, high conductivity, mechanical

flexibility, light-weight and possibility to be integrated into existing production processes.

Apart from the fact that conductive polymers are more environmentally friendly and cost-

effective than most metal containing electrode materials, the insufficient cyclic stabilities and

the high self-discharge rate of a battery in the contemporary market could also be improved.

From the hundreds of choices of conductive polymer, composites with polypyrrole (PPy)

have drawn great attention to scientists, but the performance of these materials is limited to

its non-continuous network properties. PPy itself tends to form a discrete crystal, rather than

the continuous polymer fiber. One way to improve the performance of nonmetal-based

energy storage devices would be using composite electrode materials of conductive polymers

PPy deposited as thin-layers on a suitable large surface area substrate. Various biopolymers

(agar or cellulose) may be suitable substrate materials because of their abundance in nature

and its well-established industrial use. Therefore, this project attempts to study the feasibility

of using all polymer materials mentioned above (polypyrrole and various biopolymer) in the

fabrication of rechargeable battery.

Conductive polypyrrole can be formed by the polymerization of pyrrole monomers

(System Diagram 1). The underlying principle of the proposed biopolymer-based

rechargeable battery is to make use of the redox-behavior of polypyrrole (System Diagram 2)

and then the intercalation of polymer fiber crystal in the three-dimensional hierarchical

structure of the intertwined biopolymer fibers with highly porous structure.

N

H

oxidation by Fe3+

N

Hn

N

H

N

H

N

H

N

H

n

polymerization

polar polypyrrole fiber

System Diagram 1: Polymerization of pyrrole


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N

H

N

H

N

H

N

H

N

H

N

H

N

H

N

H− e

− Oxidation

Reduction + e−

Reduced form Oxidized form

Systemic Diagram 2: Redox behavior of polypyrrole

During charging and discharging cycles, polypyrrole polymer chains are switching

between the oxidized and reduced form (System Diagram 2), by anions and electrons transfer

in polypyrrole-composite. Charging and discharging capacity were adjusted by incorporating

with other biopolymers or other carbon-based materials (such as graphite, carbon nanotubes

or graphene) so as to alter their porosity and its charging and discharging efficiency.

In order to have full development on the potential of using biopolymer based

rechargeable battery, several intrinsic factors (types of biopolymer and their composition) and

extrinsic factor (structure of electrode) are needed to optimize, including conductivity,

chemical stability, biocompatibility and the resistance to decomposition. Optimal electrodes

preferably require porous structure to provide a large surface for the electrical contact, to

allow fast ion migration between two electrodes.

Recently, there is a strong interest in the development of thin, flexible, lightweight, and

environmentally friendly batteries to meet the needs for applications such as interactive

packaging and consumer products. Therefore, this project also attempts to optimize the

performance of battery by varying its intrinsic factors, designing a low-cost, porous structure

with high surface area electrode. Finally, a paper-thin-layered biopolymer-based rechargeable

battery was successfully constructed and demonstrated, which may closely match to the

practical requirement in real situation.


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2. MATERIALS & METHODS

2.1. Preparation of the Graphite-doped and CNT-doped Cellulose-based Composite

Battery

2.1.1. Procedure

2.1.1.1.Extraction and chemical modification of cellulose

Cellulose-rich grass was cropped into several small pieces. 1 M sodium hydroxide

solution was added to the grass pieces in order to remove the lignin by alkaline digestion. The

mixture was heated gently for two hours and aged overnight. Finely-divided cellulose-grass

was remained.

The mixture was filtered and rinsed with water until it reached neutrality. Cellulose-

fibre was then treated with bleaching solution for the oxidation of C−6 hydroxyl group to

form carboxylic group. Resulting mixture was heated for one hour and aged overnight. As-

prepared plant tissues were rinsed with deionized water until neutrality was reached, and

dried inside the oven under 100oC to complete dryness. Plant tissue was grinded into powder

and creamy-white oxidized cellulose-powder was obtained

2.1.1.2.Preparation of PPy-cellulose-gelatin composite

Other plant-based electrodes were fabricated from the deviated cellulose and gelatin.

5.00 g of gelatin was dissolved into 80 cm3 of 0.5 M sodium hydroxide solution with constant

heating and stirring, until the all chemicals were completely dissolved to give pale yellow

solution, followed by suspending 5.00 g of cellulose in the resulting mixture with constant

heating and stirring for one hour. Pale yellow paste was separated by centrifugation. 5.00 g of

pyrrole solution was mixed in the 80 cm3 5% glycerol solution with the help of 20 minutes

sonication, until the solution becomes homogenous. 5.00 g of cellulose-gelatin composite was

suspended into the pyrrole-glycerol mixture. 20 cm3 of 2 M of iron (III) sulphate solution was

added to the mixture dropwise so as to induce the cationic polymerization of pyrrole.

Solution turns from yellow to dark brown, further darken to black colour. Resulting black-

coloured paste was separated by centrifugation, and rinsed by 2 M hydrochloric acid to

remove the excess physically adsorbed iron (III) sulphate solution. Black-coloured composite

was collected.

To prepare graphite/cellulose-based conductive electrode, 2.5% by weight of

graphite powder was firstly suspended and dispersed in the pyrrole-glycerol solution under

sonication for 20 minutes. Black coloured suspension was obtained. As-prepared cellulose-


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gelatin composite, prepared by the previous method mentioned above, was then added into

the resulting mixture and further stirred for a while. 20 cm3 of 2 M of iron(III) sulphate

solution was added to initiate the cationic polymerization of pyrrole. Graphite/cellulose-

gelatin composite was then stirred and aged, followed by centrifugation and moulding into

desirable dimensions. Carbon nanotube (CNT)/cellulose-based electrodes were also

synthesized by similar method, 2.5% by weight of CNT was used instead of graphite powder

in the pretreatment stage. The size of the electrode was also set as 2.5 cm × 2.5 cm.

2.1.1.3.Fabrication of thin-layered biopolymer electrodes

Thin-layered electrodes were prepared by doctor-blade method as follow: Few drops

of Triton X-100 surfactant were added to the black-coloured composite to increase the

viscosity of composite. Composite was coated on the waxy-paper, compressed into a thin-

layered structure with the thickness of 2 mm, and resized to electrode with dimensions of 2.5

cm × 2.5 cm.

2.1.1.4.Assembly of Thin-Layered Biopolymer-based Rechargeable Battery

Thin-layered battery was composed of two identical electrodes, a polyester thin

membrane as separator, and plastic thin-film as supporter. Two electrodes were placed on two

stainless steel strips respectively, which act as cathodic and anodic compartments of the

battery. Electrodes were fully absorbed with 2 M lithium nitrate solution. Separator was

sandwiched by the two compartments. Two pieces of plastic layers were utilized to stabilize

the cell and to apply pressure on the composites and the stainless steel strips to improve the

contact between these parts.

Separator

Free-standing

PPy-biopolymer composite

c o n t a c to r

Transparent plastic film

Transparent plastic film

Free-standing

PPy-biopolymer composite

Systematic Diagram 3: Assembly of Flexible Thin-layered PPy/Agar-based Composite Cell

2.1.1.5.Biopolymer-based rechargeable battery performance analysis

Charge-discharge measurements were performed in 2.0 M lithium nitrate solution as


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electrolyte. A battery cell was constructed by two identical pieces of the PPy-biopolymer

composite as cathode and anode separated by a sheet of polyester membrane. In the testing,

the battery cell was charged and discharged by applying the current ranging from 160 mA and

320 mA. To test for the long-term cycling stability, the charge-discharge measurements were

continuously repeated for at least 120 cycles. The performance of battery was also

demonstrated by powering on the motor and propeller after charging.

2.1.1.6.RESULT AND DISCUSSION

Both graphite and carbon nanotube (CNT) are porous and high-surface-area

conductive materials. Graphite has a layered-structure, while CNT has a hollow capacity.

Graphite and CNT can help embed ions, as an effective current collector, leading to an

increase in electrical conductivity and decrease in internal resistance of the composite. These

advantages can be utilized by mixing graphite or CNT into the cellulose, so as to improve the

batteries’ performance. Cellulose-based composite has a hierarchical structure with

complicated surface morphology, functional groups such as hydroxyl group, and high

porosity. Each cellulose fiber is comprised of multiple individual fibrils, which are in turn

composed of multiple microfibrils bundled. The interaction of these polymeric fibers with

CNTs is further facilitated by these properties as well as several properties of the CNTs

themselves. CNTs have been proved to have large van der Waals’ interactions with many

types of polymers. Furthermore, acid treated CNTs have carboxyl groups on the surface and

the ends, which can form strong hydrogen bonds with the hydroxyl groups in the cellulose

fibers. Because of the mechanical flexibility of CNTs and the high surface area of cellulose

fibers, together with the large water absorbability of the composites, surface contact between

CNTs and composite fibers is maximized. Upon contact, large van der Waals’ forces and

hydrogen bonding occurs, which binds the CNTs very tightly to the composite fibers.

Systematic Diagram 4 shows CNTs wrapping around composite fibers to create a 3D porous

structure.

Cellulose-fibers

Carbon nanotubes

Systematic Diagram 4: Carbon nanotubes wrapping around cellulose-fibers to form 3D


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In the electrochemical studies, graphite/cellulose-based battery was charged and

discharged for 200 cycles under 160 mA and 320 mA in stability tests respectively (Graph 1).

In first 20 cycles under 160 mA of charging, graphite/cellulose-based battery had a peak

voltage of 1.75 V and maintain steadily until 100th to 120th cycles. While under 320 mA

charging current, the peak voltage of 2.7 V in the first 20 cycles, declined to 2.5 V during

100th to 120th cycles. For CNT/cellulose-based composite, under 160 mA charging current,

the peak voltage of 2.0 V in first 20 cycles, declined slightly by 5% (1.9 V) in 100th to 120th

cycles. Under 320 mA charging current, the peak voltage was 2.8 V and declined by 3.6%

(2.7 V) during 100th to 120th cycles (Graph 2). As compared to undoped cellulose-based

electrode, both modified electrodes (graphite-doped and CNT-doped) showed a range of

3.85% to 25% surplus in peak voltage. Both conductive graphite and CNT provide large

surface area and extensive porosity on trapping the charge particles.

Graph 1: Charge and discharge cycles (right: 1 – 20, left: 100 – 120) of

the graphite/cellulose-based composite cell under 160 mA (top) and 320 mA

(bottom) charging current

0 100 200 300 400 500 600 700

0.0

0.5

1.0

1.5

2.0

Charge and discharge cycles

Cell voltage / V

Time / s

3500 3600 3700 3800 3900 4000 4100 4200

0.0

0.5

1.0

1.5

2.0


Cell voltage / V

Time / s

0 100 200 300 400 500 600 700

0.0

0.5

1.0

1.5

2.0

2.5

3.0


Cell voltage / V

Time / s

3500 3600 3700 3800 3900 4000 4100 4200

0.0

0.5

1.0

1.5

2.0

2.5

3.0


Cell voltage / V

Time / s


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Graph 2: Charge and discharge cycles (right: 1 – 20, left : 100 – 120) of

the CNT/cellulose-based composite cell 160 mA (top) and 320 mA (bottom)

charging current

Data in graph 3 showed the cycling behaviour of the graphite/cellulose-based

composite cell charging current on 160 mA and 320 mA respectively. Under charging current

of 160 mA, the battery had a charge capacity of 15.81 mAh g-1 at the initial stage, and

slightly decreased by 5.9% to 14.89 mAh g-1 by 5.9% after 100 charge-and-discharge cycles.

Under charging current of 320 mA, the battery had a charge capacity of 14.58 mAh g-1 at the

beginning and decreased by 6.1% to 13.69 mAh g-1 after 100 charge-and-discharge cycles. In

graph 8, the cycling behaviour of CNT/cellulose-based battery was shown. The battery had a

charge capacity of 19.04 mAh g-1 and gently decreased by 3.8% to 18.30 mAh g

-1 after 100

charge-and-discharge cycles under charging current of 160 mA. While under charging current

of 320 mA, the battery gave a charge capacity of 18.27 mAh g-1 at first, then slightly

decreased by 4.1% to give a charge capacity of 17.56 mAh g-1 after 100 charge-and-discharge

cycles.

0 100 200 300 400 500 600 700

0.0

0.5

1.0

1.5

2.0

2.5


Cell voltage / V

Time / s

3500 3600 3700 3800 3900 4000 4100 4200

0.0

0.5

1.0

1.5

2.0

2.5


Cell voltage / V

Time / s

0 100 200 300 400 500 600 700

0.0

0.5

1.0

1.5

2.0

2.5

3.0


Cell voltage / V

Time / s

3500 3600 3700 3800 3900 4000 4100 4200

0.0

0.5

1.0

1.5

2.0

2.5

3.0


Cell voltage / V

Time / s


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0 10 20 30 40 50 60 70 80 90 100

0

2

4

6

8

10

12

14

16

18

160 mA

320 mA

Change in charge capacity with cycle number

Charge capacity (mAh g

-1)

Cycle number

Graph 3: Cycling behavior of the graphite/cellulose-based composite cell at different

charging current (160 mA and 320 mA). A 5.9 % and 6.1% decreases in the charge

capacity were observed after 100 cycles.

0 10 20 30 40 50 60 70 80 90 100

10

12

14

16

18

20

160 mA

320 mA

Change in charge capacity with cycle number

Charge capacity (mAh g

-1)

Cycle number

Graph 4: Cycling behavior of the CNT/cellulose-based composite cell at different charging

current (160 mA and 320 mA). A 3.8 % and 4.1% decreases in the charge capacity

were observed after 100 cycles.

As compared to the cellulose-based battery (table 1), graphite/cellulose-based

battery showed +8 – 11% increase in the charge capacity under different charging current

(160 mA and 320 mA). The increase in figure can be explained from the intrinsic structure of

the composite. Cellulose fibres were randomly intertwined with each other to construct inter-

fibrous spaces in macro-mesoporous sizes. Such irregular vacancies are not favourable in

holding the ions inside. In contrast, layered graphite, with a stacking pattern, provides a

uniform separation with the inter-layer distance of 0.335 nm, which is almost the double of

the diameter of common ions (e.g. diameter of Li+ = 0.180 nm). Ions can be embedded


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regularly in between the layers, maximizing the charge holding capacity. At the same time,

the high electrically conductive properties can further reduce the internal resistance of the

battery.

Similar effect on the charge capacity by CNT doping can also be observed from the

results between the charge capacities of cellulose-based and CNT/cellulosed-based in table 1.

The CNT/cellulose-based battery showed a surplus of +30 – 40% under different charging

current. CNT/cellulose-based battery also showed increase of +20 – 28% in charging capacity

compared to the graphite/cellulose-based battery. The open-ended tubular structure with high

aspect ratio of CNT may intensify the capillary effect in the nanotubes, leading to the influx

of lithium ions into the interior tubular cavity. Also, the open-ended structure provides

barrier-free pathway for the migration and housing of ions, which further enhance the rate of

loading/unloading of ions. Moreover, the aggregation of CNTs may fill the separations of the

cellulose fibrous structures, which increases the density and the charge capacity of the final

composite.

Table 1: Comparison of charge capacity between cellulose-based model, graphite/cellulose-

based model, and CNT/cellulose-based model battery at different charging current

Charging current 160 mA 320 mA

Charging cycle 1st – 10

th 100

th – 110

th 1

st – 10

th 100

th – 110

th

Cellulose-based 14.54 mAh g−1 13.57 mAh g

−1 13.13 mAh g

−1 12.57 mAh g

−1

Graphite/cellulose-

based 15.81 mAh g

−1 14.89 mAh g

−1 14.58 mAh g

−1 13.69 mAh g

−1

Percentage change +8.73% +9.72% +11.04% +8.91%

Cellulose-based 14.54 mAh g−1 13.57 mAh g

−1 13.13 mAh g

−1 12.57 mAh g

−1

CNT/cellulose-based 19.04 mAh g−1 18.30 mAh g

−1 18.27 mAh g

−1 17.56 mAh g

−1


Graphite/cellulose-

based 15.81 mAh g

−1 14.89 mAh g

−1 14.58 mAh g

−1 13.69 mAh g

−1

CNT/cellulose-based 19.04 mAh g−1 18.30 mAh g

−1 18.27 mAh g

−1 17.56 mAh g

−1


Graph 5 represents the variations of cell voltage of CNT/agar-based battery and

CNT/cellulose-based battery under 5 hours of discharging. The cell voltage of

CNT/cellulose-based model was dropped from 2.24 V to 0.87 V in the first hour of discharge,

and keep steadily decrease to 0.60 V. While the CNT/agar-based model was decreased in less

extent throughout the 5 hours of discharging, from 1.52 V to 0.95 V. Obviously,

CNT/Cellulose-based model is able to give a high open-circuit voltage, but not a long-lasting


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stable discharge performance, while the discharge performance of CNT/agar-based model is

relatively steady and long lasting. In view of two advantages from different composite

materials, perhaps the drawback of the low stability of discharge performance in cellulose-

based model can be compensated by merging the unique characteristic of agar into cellulose-

composite in the preparation of cellulose-based electrode. Owing to the fibrous structure of

cellulose-gelatin composite and its discharging performance, it is obvious that the rate of

decrease in the cell voltage of the cellulose-based electrode is relatively higher than that of

the agar-based electrode. It may be understood from the relative porosity of the electrodes:

the charge transfer may increases with the porosity of the electrodes. High porosity may favor

the charge-and-discharge process and turns shorten the time for charging process and,

however, also the time for discharging. Idea battery should provide a stable discharging rate

and increase its service time. In view of the different structural properties of agar and

cellulose composites, agar-cellulose-gelatin composite was designed and fabricated to

combine the advantages raised from the agar composite and cellulose-gelatin composite.

Graph 5: Discharging behaviors of various CNT-doped biopolymer batteries of

CNT/agar model and CNT-cellulose model

2.2.Preparation of the Graphite-doped and CNT-doped Agar-Cellulose-based

Composite Battery

2.2.1. Procedure

Agar-cellulose-gelatin composite was prepared by the similar method as mentioned

above. 2 : 5 : 5 by weight agar-cellulose-gelatin was suspended in either graphite or CNT

pyrrole-glycerol mixture and heated with constant stirring, until all agar powder completely

0 1 2 3 4 5

0.0

0.5

1.0

1.5

2.0

2.5

CNT/cellulose compsite

CNT/agar compsite

Discharge Curve

Cell voltage / V

Time / hr

0 1 2 3 4 5

0

20

40

60

80

100


CNT/agar compsite

Discharge Curve

% change in cell voltage

Time / hr


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dissolved to give a homogenous solution. Iron(III) solution was added dropwise to induce the

cationic polymerization of pyrrole with gently stirring. Mixture was allowed to stir for a

while. Black viscous mixture was then poured to the molder for molding. The jelly-like gel

was then aged and dried inside the oven until a firm and mechanically strong with rough-

texture agar-cellulose-gelatin composite was obtained. A dimension of 2.5 cm × 2.5 cm

electrode was then prepared and ready for assembly of battery.

2.2.2. Result and discussion

The first and last 20 cycles of the 120 charge-and-discharge cycles preformed using

a current of 160 mA and 320 mA of graphite-doped or CNT-doped agar-cellulose-based

batteries were shown in graphs 10 and 11 respectively. The calculated charge capacities from

the charge curves normalized by the total weight of the active composite material were

plotted versus cycle number. Results of both cell peak voltage and charge capacity of either

graphite-doped or CNT-doped agar-cellulose battery were summarized in Table 2.

Table 2: Comparison of cell peak voltage and charge capacity in different cycles of graphite-

doped or cellulosed-doped in agar-cellulose composite cell

Charging current Graphite/agar-cellulose model CNT/agar-cellulose model


th 100

th – 110

th 1

st – 10

th

100th –

110th

Cell peak voltage (160

mA) 1.60 V 1.60 V 2.41 V 2.33 V

Cell peak voltage (320

mA) 2.08 V 1.99 V 2.58 V 2.45 V

Percentage change 160 mA : 0% ; 320 mA : −4.3% 160 mA : −3.3% ; 320 mA :

−5.3%

Charge capacity (160 mA) 15.61 mAh g−1 14.83 mAh g

−1 18.08 mAh g

−1

17.61

mAh g−1

Charge capacity (320 mA) 14.88 mAh g−1 14.69 mAh g

−1 17.92 mAh g

−1

17.42

mAh g−1

Percentage change 160 mA : −5.0% ; 320 mA :

−1.3%

160 mA : −2.6% ; 320 mA :

−2.8%

Graph 6 and 7 show that the materials still cycles well after 100 cycles at a rate of

either 160 mA or 320 mA. Results were seen in Graph 12 (left), the decrease in the charge

capacities of graphite-doped battery during the experiment was only 5.0% (from 15.61 mAh

g−1 to 14.83 mAh g

−1) and 1.3% (from 14.88 mAh g

−1 to 14.69 mAh g

−1) after a long run

under charging current of 160 mA and 320 mA respectively. Similar results, shown in Graph


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8 (right), can also be found in the CNT-doped battery; around 2.7 % decreases in the charge

capacities were observed after 100 cycles under both charging currents of 160 mA and 320

mA. Similarly, the overall performance of CNT-doped battery is better than that of graphite-

doped battery. The main focus of this section is to improve the discharge performance of the

cellulose-based battery through increasing the density of biopolymer fiber. Based on the

texture and weight of the agar-cellulose-based electrode with same dimensions, heavier,

rough and continuous film provide a good evidence for the better intercalation of polymer

chains in different chain length. Moreover, the shrinkage of agar-polymer film can be

observed in the aging process. Shrinkage of polymer exerts the inwards force to the

composite for further compression of polymer chains. It is known that agar polymer is a

thermoplastic with low mechanical strength and resistance to heat. Surprisingly, the texture

and framework of the agar-cellulose-composite were retained as firm as the original state

even after 120 charge-and-discharge cycles or long charging process for the discharging test.


the graphite/agar-cellulose-based composite cell under 160 mA (top) and 320 mA


0 100 200 300 400 500 600 700

0.0

0.5

1.0

1.5

2.0


Cell voltage / V

Time / s

3600 3700 3800 3900 4000 4100 4200 4300

0.0

0.5

1.0

1.5

2.0


Cell voltage / V

Time / s

0 100 200 300 400 500 600 700

0.0

0.5

1.0

1.5

2.0

2.5

3.0


Cell voltage / V

Time / s

3600 3700 3800 3900 4000 4100 4200 4300

0.0

0.5

1.0

1.5

2.0

2.5

3.0


Cell voltage / V

Time / s


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the CNT/agar-cellulose-based composite cell under 160 mA (top) and 320 mA


Graph 8: Cycling behavior of the graphite-doped (left) and CNT-doped (right) on agar-

cellulose-based composite cell at different charging currents (160 mA and 320 mA).

It is understood that incorporating non-fibrous agar material into the fibrous

cellulose material may raise the negative effect on the peak voltage of the cellulose-based

0 100 200 300 400 500 600 700

0.0

0.5

1.0

1.5

2.0

2.5


Cell voltage / V

Time / s

3500 3600 3700 3800 3900 4000 4100 4200

0.0

0.5

1.0

1.5

2.0

2.5


Cell voltage / V

Time / s

0 100 200 300 400 500 600 700

0.0

0.5

1.0

1.5

2.0

2.5

3.0


Cell voltage / V

Time / s

3500 3600 3700 3800 3900 4000 4100 4200

0.0

0.5

1.0

1.5

2.0

2.5

3.0


Cell voltage / V

Time / s


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battery during charge-and-discharge process. After taking comparison, the percentage

changes of peak voltage in graphite-doped cellulose based or agar-cellulose based model

were fall within 10%, or varied in the range of −5% to +1% for CNT-doped cellulose based

or agar-cellulose based model (Table 3). It seems that there is no great negative impact on the

peak voltage in each cycle after introducing foreign agar-polymer chain in the cellulose-based

composite.

Table 3: Comparison of peak voltage in different cycles of graphite-doped or CNT-doped with

different biopolymer composite (cellulose-based composite or agar-cellulose-

based composite).

Charging current 160 mA 320 mA


th 100

th – 110

th 1

st – 10

th 100

th – 110

th

Graphite/cellulose 1.77 V 1.78 V 2.66 V 2.51 V

Graphite/agar-

cellulose 1.60 V 1.60 V 2.41 V 2.33 V

Percentage change –9.60 % –10.1 % –9.40 % –7.17 %

CNT/cellulose 2.06 V 1.98 V 2.75 V 2.60 V

CNT/agar-cellulose 2.08 V 1.99 V 2.58 V 2.45 V

Percentage change +0.97 % +0.51 % –6.18 % –5.77 %

Graph 9 showing the variation of cell voltage of different CNT-doped biopolymer

composite cells – agar-based, cellulose-based and agar-cellulose-based, it is clearly presented

that the stability of cell voltage in the agar-cellulose based model was greatly improved when

comparing to the cellulosed-based model, with almost 2-folds increase. Factors like persistent

discharging properties from agar, rigid fibrous nature of cellulose, and high charge capacity

of CNT are all conserved and well-presented in CNT/agar-cellulose-based model. These

advantages can also be found in other models – graphite-doped or undoped agar-cellulose-

based battery (Graph 10). Although using agar-cellulose-based composite may sacrifice the

peak voltage of the battery up to –10%, great enhancement on the stability of discharging

performance outweighs the little loss in the battery peak voltage. Therefore, agar-cellulose-

composite serves as the final choice of material for electrode. The enhancement on the

stability of discharging performance can be rationalized from the highly-dense, intertwining

biopolymer fiber structure, which providing a good platform for loading and unloading

charges in an appropriate rate.


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Graph 9: Discharging behaviors of various CNT-doped biopolymer batteries of CNT/agar

model; CNT/cellulose model and CNT/agar-cellulose model.

Graph 10: Discharging behaviors of graphite or CNT doped agar-cellulose-gelatin composite

(i) CNT/agar-cellulose-based composite; (ii) Graphite/agar-cellulose-based

composite; (iii) agar-cellulose-based composite

3. CONCLUSION

During this research, several challenging problems needed to be addressed. This

includes choosing appropriate biopolymers as the building block of electrode; designing and

reconstructing the more effective and low-cost cellulose-based electrode; improving the

charging capacity of biopolymer electrode by incorporating those conductive nanomaterials

such as graphite and carbon nanotubes; and enhancing the discharging performance by

altering the density of biopolymer electrode. Various types of modifications are summarized

as table follows:

0 1 2 3 4 5

0.0

0.5

1.0

1.5

2.0

2.5


CNT/agar compsite

CNT/agar-cellulose composite

Discharge Curve

Cell voltage / V

Time / hr

0 1 2 3 4 5

0

20

40

60

80

100


CNT/agar compsite

CNT/agar-cellulose composite

Discharge Curve

% change in cell voltage

Time / hr

0 1 2 3 4 5

1.0

1.5

2.0

2.5

3.0

Undoped

Graphite-doed

CNT-doped

Discharge Curve

% change in voltage

Time / hr


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Table 4: Summary of types of modification in this project

Problem Idea Method

Non-renewable metal-based

rechargeable battery

Battery made from the

renewable materials

Battery made from

renewable, green

materials (biopolymers

such as agar or cellulose)

Insulating biopolymers

restrict the development on

the energy storage device

Increase the electrical

conductivity

Coating with the electrical

conductive polymer

(polypyrrole or

polyaniline)

Non-fibrous, low mechanical

strength agar polymers

provide a fatigue nature, low

surface area and porosity for

energy storage.

Another biopolymers with high

surface, porous structure with

high mechanical strength

Fibrous cellulose-based

biopolymer as the final

choice

Polypyrrole/cellulose-based

battery shows a lower

charging capacity

Increase its charging capacity

by incorporating with other

conductive porous materials

Graphite or carbon

nanotubes as the active

materials

Rapid drop in the discharging

voltage in the cellulose-based

battery

Extend the stability of voltage

in the discharging process by

modifying the density of

composite

Combining agar and

cellulose to form a high

density composite

CNT/cellulose-based battery demonstrated was found to have a poor stability in

discharging, dropped by 61.2% in cell voltage. With reference to the CNT/agar-based battery,

it had a relatively better stability in discharging (dropped by 37.5%). Hence, the CNT/agar-

cellulose-based battery was fabricated, to combine the advantages of cellulose (high peak

voltage) and agar (higher discharging stability). In CNT/agar-cellulose-based battery model,

the peak voltage remains unchanged as 2.08 V, while its stability also increases by 2-times

compared to CNT/cellulose battery model. It can be explained that agar-cellulose polymer

achieve a better intercalation of polymer chains, providing an order 3D electrode

configuration design. Four different models of biopolymer battery achieved significantly

improved performance. Almost 95% of materials used in this novel design are biodegradable

and green, which can be directly extracted from plants. It is believed that this is the first

report of the design and development of green rechargeable battery using various common

biopolymers.

Lastly, the extension of this project can go into different categories including

extending the source of cellulose, substrate of electrode, choice of the dopant, or even the


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structure of the battery. Beside the cellulose, other polysaccharides, such as lignocellulose,

chitin, pectins, which are commonly found in those agricultural wastes like sawdust, wheat or

crop, can be used as the alternative in making substrate of electrode. Also, the source of

cellulose can also be extended from the herbaceous plant to those woody agricultural wastes.

In this project, composites were synthesized from common biopolymer. But, if the polymer

battery step into the mass production stage, using some commercially available or ready used

materials for the composite can further shorten the production lead-time and increase the

efficiency of the mass production. Hence, feasibility of using common flexible woven

materials as the electrode can be conducted to further extend its flexibility, practicality and its

application. Regarding the choice of dopant, the purpose of adding dopant is to further

modify the electrochemical properties of the electrode. Recently, graphene has drawn

scientists great attention because of this extraordinary electrical conductive properties and its

textile strength. The battery performance may also be strengthened if graphene is used.

Finally, although the development of biopolymer-based rechargeable battery is still at the

beginning stage, we truly believe that the wide application of biopolymer-based rechargeable

battery will come into reality in the near future.

4. REFERENCES

[1] Tarascon, J. M., Armand, M. Nature 2001, 414, 359-367.

[2] Winter, M., Brodd, R. Chem. Rev. 2004, 104, 4245-4269.

[3] Nuraje, N., Su, K., Yang, N. I., Matsui, H. ACS Nano 2008, 2, 502-506.

[4] Hu, L., Pasta, M., Mantia, F. L., Cui, L., Jeong, S., Deshazer, H. D., Choi, J. W., Han, S. M.,

Cui, Y. Nano Lett. 2010, 10, 708-714.

[5] Hu, L., Wu, H., Mantia, F. L., Yang, Y., Cui, Y. Nano Lett. 2010, 10, 5843-5848.

[6] Hirala, P., Imaizumi, S., Unalan, H. E., Matsumoto, H., Minagawa, M., Rouvala, M., Tanioka,

A., Amaratunga, G. A. J. ACS Nano 2010, 5, 2730-2734.


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5. APPENDIX

� Summary of the charge capacity of various biopolymer-based batteries

Sample

No. Nature

Charge capacity / mAh g−1

160 mA 320 mA

1. Agar-based battery 6.87 5.27

2. Cellulose-based battery 13.57 12.57

3. Agar-cellulose-based battery 12.32 11.23

4. Graphite-doped cellulose-based battery 14.89 13.69

5. CNT-doped cellulose-based battery 18.30 17.56

6. Graphite-doped agar-cellulose-based battery 14.83 14.69

7. CNT-doped agar-cellulose-based battery 17.61 17.42

LO Chun Kit Jason WONG Chi Sum

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