Polymer battery employing polyacenic semiconductor

Polymer battery employing polyacenic semiconductor

Synthetic Metals, 18 (1987) 6 4 5 - 6 4 8 6 z~5 POLYMER BATTERY EMPLOYING POLYACENIC SEMICONDUCTOR S. YATA, Y. HATO, ~ SAKURAI and T. OSAKI Devel...

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Synthetic Metals, 18 (1987) 6 4 5 - 6 4 8

6 z~5

POLYMER BATTERY EMPLOYING POLYACENIC SEMICONDUCTOR

S. YATA, Y. HATO, ~

SAKURAI and T. OSAKI

Development Laboratories,

Kanebo Ltd., Miyakojima-ku,

osaka 534 (Japan)

K. TANAKA and T. YAMABE Department of Hydrocarbon Chemistry and Division of Molecular Engineering, Faculty of Engineering,

Kyoto University,

Sakyo-ku,

Kyoto 606

(Japan)

ABSTRACT Recently, we have succeeded to prepare a new type of polyacenic semiconductor (PAS) which is made in the form of sheet or plate with a bulk density of about 0.4g/cm 3 from phenol-formaldehyde

resin through pyrolytic process. A typical PAS

has a H/C molar ratio of 0.25 and an electrical conductivity of 10-5S/cm. The specific surface area is above 2000m2/g and the bending strength is 100150kg/cm 2. We constructed two types of storage batteries using a disk formed PAS as electrode and solution of IM LiCIO 4 in SL + y-BL

(i:i in volume)

as electrolyte

These batteries displayed excellent reversibility for electrochemical dopingundoping process and very small self-discharge.

We believe PAS battery is one of

the first application of conductive polymers for practical use. INTRODUCTION In the last decade, extensive studies on conductive polymers have been performed from both experimental and theoretical point of view. Especially batteries employing these polymers as electrode have been investigated explosively due to its large capacity and high power density.

However,

these

batteries show rapid self-discharge and short cycle life, which restrict their application to laboratory-stage. A polyacenic semiconductor, which is prepared by pyrolytic treatment of phenolformaldehyde resin, shows air-stability and can be doped with an electron donor and acceptor by a well known manner

[1-3]. Recently, we have improved the

pyrolytic treatment and prepared a new type of polyacenic material

(PAS) which

has suitable structure for electrochemical doping-undoping with bulky ions such as

(C2H5)4 N+, CI04-, etc. In this paper, we report fundamental properties of PAS

and its application to a storage battery.

0379-6779/87/$3.50

© Elsevier Sequoia/Printed in The Netherlands

646 RESULTS A n e w type of p o l y a c e n i c s e m i c o n d u c t o r

(PAS)

We r e p o r t e d that p o l y a c e n i c s e m i c o n d u c t o r p r e p a r e d f r o m p h e n o l - f o r m a l d e h y d e r e s i n in p y r o l y t i c p r o c e s s is a i r - s t a b l e and it can be d o p e d s u c c e s s f u l l y w i t h 12 or N a b y a w e l l k n o w n m a n n e r

[1-3]. However, w e found that it was d i f f i c u l t to

dope this m a t e r i a l e l e c t r o c h e m i c a l l y w i t h b u l k y ions such as BF4-.

(C2H5)4N+ , CIO 4- and

In o r d e r to get a m a t e r i a l suitable for e l e c t r o c h e m i c a l doping, w e p r e p a r e d

a new type of p o l y a c e n i c s e m i c o n d u c t o r

(PAS) from p h e n o l - f o r m a l d e h y d e resin by

adding ZnCI 2 in the p r o c e s s of pyrolysis. p o r o u s structure as shown in Fig. 2500m2/g

(BET method).

This p o l y a c e n i c s e m i c o n d u c t o r has

1 and a large specific surface area of 1800 -

This m o r p h o l o g y of PAS seems to enable it to be d o p e d

s m o o t h l y w i t h b u l k y ions. The H/C m o l a r r a t i o and the e l e c t r i c a l c o n d u c t i v i t y can b e c o n t r o l l e d b y p y r o l y t i c t e m p e r a t u r e in the range of 0.15 - 0.3 and 10 -7 10-2S/cm, respectively.

Moreover,

PAS can be m a d e in the form of p l a t e or film

w i t h a b u l k d e n s i t y of 0.2 - 0 . 5 g / c m 3 and w i t h a b e n d i n g s t r e n g t h of i00 1 5 0 k g / c m 3. These f l e x i b i l i t i e s in p r o p e r t i e s and f o r m a t i o n are favorable in i n d u s t r i a l usage as w e l l as the a i r - s t a b i l i t y o f ' t h i s material.

Fig. i. A cross s e c t i o n p i c t u r e drawn in the p i c t u r e is 5~m.

(SEM) for PAS. The length of the solid line

E l e c t r o c h e m i s t r y of PAS and its a p p l i c a t i o n to storage b a t t e r y All PAS u s e d in e l e c t r o c h e m i c a l m e a s u r e m e n t and b a t t e r y w e r e disk formed samples w i t h a

H/C m o l a r ratio of 0.25, an e l e c t r i c a l c o n d u c t i v i t y of 10-5S/cm,

a s p e c i f i c surface area of 2 0 0 0 m 2 / g and a d e n s i t y of 0.4g/cm 3. All cells w e r e c o n s t r u c t e d b y s a n d w i c h i n g a p i e c e of glass cloth s e p a r a t o r b e t w e e n PAS as cathode and PAS or Li as anode, u s i n g n o n - a q u e o u s e l e c t r o l y t e solution.

647 Fundamental electrochemistry of PAS Fig. 2 shows the relation between potential vs. Li/Li + and amount of dopant measured under a constant current of 0.5mA/cm 2 in IM LiCIO 4 in sulfolane. The degree of oxidation or reduction per carbon of PAS electrode was calculated from the amount of charge passed and from the weight of PAS

(50mg).

In this

figure, the charge-discharge curves for both n-doping and p-doping region change continuously and show symmetry around no-doping point of 3V. This behavior may be interpreted to correspond that PAS consists of fractions with various sized condensed aromatic rings. When we discharged from 4.5V to iV under imA in this cell, charge of 220Ah/kg flowed from the PAS electrode, and a value of 550Wh/kg was obtained in energy density based on the weight of PAS. Processes of n-doping in Fig. 2 display higher coulombic efficiency in comparison with p-doping, which would be ascribed to decomposition of electrolyte above 4V in the case of p-doping+

LiCI04

in 5L

>4 \ 0

2

i

6

4

2

0

2

4

6

8

i

reduction(%) /

/~ \ oxidation(%)

Fig. 2. Doping-undoping processes for Li/ IM LiClO 4 in SL /PAS cell. Definition of reductio~ and oxidation is written in the text.

Application to storage battery We assembled two types of storage batteries. The first one is Li/PAS battery employing PAS disk

(15mm~ x 1.2tmm, 85mg) as cathode and IM LiCIO 4 in SL + ~-

butyrolactone

(i:i in volume) as electrolyte. The other is PAS/PAS battery using

two PAS disks

(15mm~ x 0.75mm t, 53mg) as electrodes and the same electrolyte.

The Li/PAS battery shows excellent reversibility when it is operated in the voltage range of 4.0 - 2.0V. In this range, the battery demonstrates the capacity of 7mAh under 2mA discharge, and 6mAh under 20mA at room temperature. When it was charged at 4.0V for i hour, the voltage of this battery still remains at 3.9V after standing at room temperature for 200 hours. This voltage change indicates very small self-discharge in Li/PAS battery.

648

The other type of battery employs PAS as both cathode and anode. The capacity and the specific capacity for this battery are 2.2mAh and 37F/g under ImA discharge from 2.0V to 0V. The battery shows a capacity of 1.9mAh even at -30°C, and 2.0mAh under discharge of 10mA. The inner resistance increases continuously from 15~ to 40~ with decreasing temperature from 30°C to -30°C. Cycle performance and self-discharge behavior for this battery are illustrated in Fig.

3. Panel-A

in this figure indicates that the characteristics of this battery show no change after deep charge-discharge

cycles of 3000 times. Data on Panel-B represents

that the battery can work as a back-up source for a long term. In conclusion,

PAS has suitable structure and property for electrode material,

and both Li/PAS and PAS/PAS battery gain an advantage over common storage batterie

cycle number 40 JE

< E

1000 panel- A

2000

3000

4000

>,2

L

(3. U

> \ (J

d

0 3

panel. - B

2

c

o

1 I I

00 ~.1

t LIIIII

t

I lltttll

I

10 time /

I Illlltl

t

10 2

I IIlllll

10 3

h

Fig. 3. A long term performance for PAS/PAS battery;Panel-A is the result of cycle test and Panel-B self-discharge behavior.

REFERENCES 1

S. Yata

2

K. Tanaka, K. Ohzeki, T. Yamabe and S. Yata, Synth. Met., 9 (1984) 41.

3

(Kanebo Ltd.), E.P. Pat 0,067,444.

K. Tanaka, S. Yamanaka, T. Yamabe, K. Yoshino, G. Ishii and S. Yata Phys. Rev. B, 32 (1985) 6675.

4

S. Yata

(Kanebo Ltd.)j E.P. Pat 0,149,497.