An Electrode-Active Material in Aqueous and Nonaqueous Electrolytes

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x

R. B. KANER, A. G. MACDIARMID, and R. J. ΜΑΜΜΟΝΕ Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104 A potentially large, new, unexpected f i e l d of con ducting polymers i s opened up by the discovery that (CH) can be doped electrochemically, in aqueous solution to the metallic regime without the i n c l u sion of oxygen. For example, use of (CH) film as the anode in an electrochemical cell employing NaAsF6 in 52% aqueous HF as an electrolyte gives f l e x i b l e , golden films (σ =10-100 ohm cm ). The energy density, power density and other characteristic pro perties of four different types of rechargeable bat teries using (CH) electrodes are described. The batteries are i l l u s t r a t e d below by equations rep resenting their discharge reactions: Type I : (CH) cathode/Li anode: (i) [CΗ (ClO ) y] + x

x

-1

-1

x

+y

-

x

4

xyLi -> (CH) + xyLiClO , and (ii) (CH) x

4

x

x

+

-y

xyLi -> [Li+yCH ] ; Type II: (CH) cathode/(CH) x

x

x

anode: ( i ) (CH) + [Li+yCH-y] -> 2[Li+y/2CH-y/2] , x

and

x

+y

(ii)

[CH (ClO )- ] 4

y x

x

-y

+ [Li+ CH ] y

x

-> 2(CΗ)x

+ xyLiClO . 4

Aqueous E l e c t r o c h e m i s t r y o f ( C H )

Y

When t r a n s - ( C H ) f i l m i s p a r t i a l l y o x i d i z e d ( i . e . p - d o p e d ) by bromine, i o d i n e , a r s e n i c p e n t a f l u o r i d e , e t c . i t s c o n d u c t i v i t y i n c r e a s e s by ~ e i g h t o r d e r s o f m a g n i t u d e and i t i s c o n v e r t e d t o an " o r g a n i c m e t a l " having a l l the e l e c t r o n i c p r o p e r t i e s of a c o n v e n t i o n a l metal ( 1 - 3 ) . U n t i l r e c e n t l y i t had been b e l i e v e d t h a t a l l p - d o p e d m a t e r i a l was v e r y u n s t a b l e i n t h e p r e s e n c e o f w a t e r . When t h e p r e s e n t s t u d y was u n d e r t a k e n t h e r e w e r e o n l y two a p p a r ent e x c e p t i o n s to t h i s water i n s t a b i l i t y . The f i r s t e x c e p t i o n i n v o l v e d t h e e l e c t r o c h e m i c a l o x i d a t i o n o f a p i e c e o f ( C H ) f i l m when i t was p l a c e d i n a n aqueous 0 . 5 M x

X

0097-6156/84/0242-0575$06.00/0 © 1984 American Chemical Society Davidson; Polymers in Electronics ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

576

POLYMERS IN ELECTRONICS

s o l u t i o n o f K I a n d was a t t a c h e d t o t h e p o s i t i v e t e r m i n a l o f a 9V d r y c e l l , t h e o t h e r t e r m i n a l b e i n g a t t a c h e d t o a p l a t i n u m c o u n t e r e l e c t r o d e immersed i n t h e s o l u t i o n . Doping took p l a c e i n a few m i n u t e s t o g i v e ( C H I ( ) . 0 7 ) x b a v i n g a c o n d u c t i v i t y i n t h e m e t a l l i c regime ( 4 ) . The sum o f t h e e l e m e n t a l a n a l y s e s f o r C., H and I was 9 9 . 8 % . T h i s showed t h a t no r e a c t i o n w i t h w a t e r , t o i n c o r p o r a t e oxygen i n t o t h e ( C H ) , had t a k e n p l a c e , a t l e a s t d u r i n g t h e t i m e needed f o r d o p i n g . A s t i m e p r o c e e d e d , i t was b e l i e v e d t h a t t h e a n a l y s i s must h a v e b e e n i n e r r o r a n d t h a t o x y g e n s u r e l y must h a v e b e e n i n c o r p o r a t e d d u r i n g t h e d o p i n g p r o c e s s s i n c e i t h a s b e e n shown t h a t ( C H l 3 y ) i s a p o l y c a r b o n i u m i o n ( 1 - 3 ) , [ C H ^ l p y l x a n d c a r b o n i u m i o n s a r e known t o r e a c t r e a d i l y w i t h w a t e r e s p e c i a l l y i n s o l u t i o n s whose pH i s c l o s e t o neutral. H o w e v e r , G u i s e p p i - E l i e a n d Wnek ( 5 ) h a v e r e c e n t l y d e m o n s t r a t e d a s e c o n d e x c e p t i o n by s h o w i n g t h a t ( C H I Q . 2 1 ) X e x h i b i t s u n e x p e c t e d s t a b i l i t y when i m m e r s e d i n s o l u t i o n s o f v a r y i n g pH v a l u e s and v a r y i n g c h l o r i d e i o n c o n c e n t r a t i o n s . I n order t o determine whether t h i s unexpected water s t a b i l i t y was r e s t r i c t e d o n l y t o t h e c a s e where t h e d o p a n t a n i o n was I3, f u r t h e r e l e c t r o c h e m i c a l d o p i n g e x p e r i m e n t s i n aqueous s o l u t i o n s were p e r f o r m e d . A p i e c e o f ( C H ) f i l m (2cm χ 2cm) a n d a p i e c e o f p l a t i n u m f o i l were p l a c e d i n a s a t u r a t e d s o l u t i o n ~ 0.5M NaAsFfc i n 52% aqueous H F . The ( C H ) was a t t a c h e d t o t h e p o s i t i v e e l e c t r o d e and t h e p l a t i n u m t o the n e g a t i v e e l e c t r o d e , res p e c t i v e l y , o f a d . c . power s u p p l y . A constant p o t e n t i a l of l . O V was a p p l i e d b e t w e e n t h e e l e c t r o d e s f o r ~ 30 m i n u t e s a n d t h e f i l m was t h e n washed i n 52% HF a n d pumped i n t h e vacuum s y s t e m f o r 18 h o u r s . I n s e v e r a l d i f f e r e n t e x p e r i m e n t s , c a r r i e d out u n der s l i g h t l y d i f f e r e n t c o n d i t i o n s , f l e x i b l e , golden f i l m s having good m e t a l l i c c o n d u c t i v i t y (σ - 10 t o 100 o h n T ^ c n T ) were o b tained. E l e m e n t a l a n a l y s i s showed t h a t t h e f i l m s c o n t a i n e d no o x y g e n . The f l u o r i n e c o n t e n t v a r i e d f r o m one p r e p a r a t i o n t o a n o t h e r , e.g. [CH" (ASF )Q ] , (C+H+As+F = 100.2%) a n d X

x

X

X

1

K

J

#

0

2

6

5

#

1

0

2

6

x

[CH (AsF )Q ] , (C+H+As+F = 1 0 0 . 3 % ) . The n a t u r e o f t h e dopant s p e c i e s and the cause of the v a r i a b l e f l u o r i n e c o n tent i s currently being investigated. I t i s believed that the d o p a n t p r o b a b l y c o n s i s t s of a m i x t u r e o f t h e ( A s F ) ~ a n d ( A s F ^ ) " " ions. The f a c t t h a t ( C H ) c a n be doped t o t h e m e t a l l i c r e g i m e e i t h e r w i t h i o d i n e or w i t h a r s e n i c - f l u o r i n e species without the i n c l u s i o n of oxygen suggests the p o s s i b i l i t y of an e x t e n s i v e aqueous c h e m i s t r y n o t o n l y f o r ( C H ) b u t a l s o p o s s i b l y f o r o t h e r conducting polymers. The l o w r e a c t i v i t y o f t h e ( C H * y ) i o n i n t h e s e c a s e s may be r e l a t e d t o t h e f a c t t h a t t h e p o s i t i v e c h a r g e i s b e l i e v e d t o be d e l o c a l i z e d over a p o s i t i v e s o l i t o n , c o n s i s t i n g of a p p r o x i m a t e l y 15 CH u n i t s ( 6 - 7 ) . Thus t h e c a r b o n atoms i n a CH u n i t w o u l d be l e s s s u s c e p t i b l e t o n u c l e o p h i l i c a t t a c k by 0 H ~ o r H 0 t h a n i f t h e c h a r g e were l o c a l i z e d on o n l y one c a r b o n a t o m . I t seems n o t u n l i k e l y t h a t t h e s i z e o f a p o s i t i v e s o l i t o n may v a r y w i t h t h e s i z e and p o l a r i z a b i l i t y o f t h e c o u n t e r a n i o n . M o r e o v e r , t h e + 0

0 2 9

4 e 7

e 0 2 9

x

6

X

X

2

Davidson; Polymers in Electronics ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

44.

PA: An Electrode-Active

KANER ET AL.

577

Material

ease of h y d r o l y s i s of the may, t h e r e f o r e , f e c t e d by t h e n a t u r e o f t h e c o u n t e r a n i o n . Rechargeable B a t t e r i e s Using (CH)

F i l m as

V

a l s o be

af

Electrodes

We h a v e shown p r e v i o u s l y t h a t ( C H ) f i l m c a n be o x i d i z e d a n d r e duced i n r e v e r s i b l e e l e c t r o c h e m i c a l r e a c t i o n s ( 8 - 9 ) . T h i s makes i t a n i n t e r e s t i n g m a t e r i a l t o s t u d y as a p o t e n t i a l l y u s e f u l e l e c troactive electrode material. Four d i f f e r e n t k i n d s of b a t t e r i e s e m p l o y i n g ( C H ) e l e c t r o d e s have been s t u d i e d . The d o p a n t c o n c e n t r a t i o n s g i v e n f o r t h e f o u r t y p e s of s e a l e d b a t t e r y c e l l s d i s c u s s e d b e l o w a r e b a s e d on t h e coulombs p a s s e d d u r i n g t h e c h a r g i n g a n d / o r d i s c h a r g i n g p r o c e s s e s a n d on t h e w e i g h t o f t h e ( C H ) f i l m employed. X

X

X

T y p e I : P o l y a c e t y l e n e C a t h o d e i n C o n j u n c t i o n w i t h a_ L i t h i u m Anode : (i) p - d o p e d ( C H ) c a t h o d e a n d L i anode* C e l l s were c o n s t r u c t e d f r o m c i s - p o l y a c e t y l e n e f i l m ( t h i c k n e s s ~ 0.1mm; ~ 3 . 5 m g / c m ) and l i t h i u m m e t a l immersed i n an e l e c t r o l y t e of 1.0M L1C104 i n p r o p y l e n e c a r b o n a t e ( P . C . ) . The o v e r a l l c h a r g i n g p r o c e s s i n w h i c h t h e ( 0 Η ) i s o x i d i z e d and the L i i s reduced i s r e p r e s e n t e d by t h e e q u a t i o n : y

2

χ

(CH)

X

+ xyLi (C10 )~ + +

4

[CH^(C10 )~] 4

χ

+ xyLi

(1)

where y < 0 . 0 7 . R e v e r s a l o f t h e a b o v e r e a c t i o n may be o b t a i n e d on d i s c h a r g i n g a t a f i x e d a p p l i e d p o t e n t i a l o f 2 . 5 V , t h e p o t e n t i a l ( v s . L i ) of p a r e n t , u n o x i d i z e d ( C H ) i n t h i s e l e c t r o l y t e ( l O ) . S i g n i f i c a n t o x i d a t i o n of the ( C H ) o c c u r s o n l y a t an a p p l i e d p o t e n t i a l g r e a t e r t h a n 3 . 1 V ( 1 0 ) . A f t e r t h e o n s e t of o x i d a t i o n , t h e open c i r c u i t v o l t a g e , V , r i s e s r a p i d l y w i t h i n c r e a s i n g o x i d a t i o n up t o o x i d a t i o n l e v e l s o f ~ 1% a n d t h e n i n c r e a s e s more s l o w l y ( 1 1 ) . The r e l a t i o n s h i p b e t w e e n c e l l p o t e n t i a l a n d d e g r e e o f o x i d a t i o n u n d e r v a r i o u s c o n d i t i o n s has b e e n s t u d i e d a t o x i d a t i o n l e v e l s up t o 7%. D i f f u s i o n of ( C 1 0 ) " i o n s from the e x t e r i o r t o t h e i n t e r i o r o f a 200Â ( C H ) f i b r i l f o l l o w i n g a charge c y c l e causes the V t o f a l l on s t a n d i n g . Conversely, a f t e r a p a r t i a l discharge c y c l e , the V r i s e s as ( C 1 0 A ) ~ i o n s d i f f u s e from the i n t e r i o r to the e x t e r i o r of a f i b r i l (11). X

X

o

c

4

X

o

c

Q C

Coulombic e f f i c i e n c i e s , ( Q d i s c h a r g e / Q c h a r g e ) where ^ c h a r g e r e f e r s t o t h e t o t a l coulombs i n v o l v e d i n a g i v e n c h a r g e p r o c e s s and Qdischarge f e r s t o t h e t o t a l coulombs i n v o l v e d i n a d i s c h a r g e p r o c e s s t o 2 . 5 V , have been d e t e r m i n e d f o r s e v e r a l d i f f e r e n t l e v e l s of o x i d a t i o n ( 1 1 ) . Corresponding energy e f f i c i e n c i e s h a v e a l s o been m e a s u r e d . They a r e ( o x i d a t i o n , c o u l o m b i c e f f i c i e n c y , e n e r g y e f f i c i e n c y ) : 1.54%, 1 0 0 . 0 % , 8 0 . 8 % ; 2 . 0 1 % , 99.2%, 79.7%; 2.17%, 100.1%, 81.5%; 2.51%, 95.8%, 78.2%; 4.0%, 89.5%, 72.8%; 6.0%, 85.7%, 68.2%. S t u d i e s h a v e b e e n made o f t h e change i n v o l t a g e d u r i n g c o n s t a n t c u r r e n t d i s c h a r g e s o f a 7% o x i d i z e d f i l m a t 0.1mA 1 0 0

r e


578


( 1 9 . 5 A / k g ) , 0.55mA ( 1 0 7 A / k g ) a n d a t 1.0mA ( 1 9 5 A / k g ) . Values i n parentheses r e f e r t o the discharge current normalized p e r kg o f [CH(Cl04)o.07]x e m p l o y e d . The c o r r e s p o n d i n g e n e r g y d e n s i t y v a l u e s upon d i s c h a r g e t o 2.5V a n d 3.0V, between w h i c h p o t e n t i a l s t h e v o l t a g e b e g i n s t o d r o p r a p i d l y a r e 255Whr/kg a n d 217Whr/kg, respectively. The e n e r g y d e n s i t y v a l u e s a r e b a s e d o n l y o n t h e mass o f t h e e l e c t r o a c t i v e m a t e r i a l i n v o l v e d and a r e c a l c u l a t e d u s i n g t h e w e i g h t o f t h e [CH(Cl04)o.rj7]x employed and t h e weight o f L i consumed i n t h e d i s c h a r g e r e a c t i o n ( t h e r e v e r s e r e a c t i o n t o t h a t g i v e n by t h e above e q u a t i o n f o r t h e c h a r g i n g r e a c t i o n ) . The a v e r a g e power d e n s i t i e s f o r t h e 0.1mA, 0.55mA a n d t h e 1.0mA d i s c h a r g e s a r e 70W/kg, 354W/kg a n d 591W/kg, r e s p e c t i v e l y ( 1 1 ) . Maximum power d e n s i t i e s , P , were o b t a i n e d a t t h e b e g i n n i n g o f a d i s c h a r g e c y c l e u s i n g a n e x t e r n a l l o a d whose r e s i s t a n c e was matched t o t h e i n t e r n a l r e s i s t a n c e o f t h e c e l l . V a l u e s were o b t a i n e d by m e a s u r i n g V a n d / o r I ( V a n d I = v o l t a g e a n d c u r rent r e s p e c t i v e l y a t the very beginning of a discharge cycle) and Rj£ ( t h e e x t e r n a l l o a d r e s i s t a n c e ) by u s e o f t h e r e l a t i o n m a x #

m

s

^P

8

P

m

P

m

a n d

max. - V m ' n,ax = V * *

/°

r

m

P

ma* = Φ * ·

The v a l u e s o b t a i n e d , ~ 30,000W/kg, were r e l a t i v e l y i n d e p e n d e n t of e i t h e r t h e e x t e n t o f o x i d a t i o n o f t h e [ C H ( C 1 0 4 ) ] o r the a b s o l u t e weight o f t h e [ C H ( C l 0 4 ) ] employed ( 1 1 ) . A l l o f t h e above e l e c t r o c h e m i c a l c h a r a c t e r i s t i c s o f t h e c e l l a r e e x t r e m e l y s e n s i t i v e t o t h e method o f c e l l c o n s t r u c t i o n , p r e s ence o f i m p u r i t i e s ( e s p e c i a l l y o x y g e n ) , r e l a t i v e r a t i o o f e l e c t r o l y t e t o ( C H ) , method o f c h a r g i n g , e t c . y

y

x

x

V

(ii) n e u t r a l ( C H ) c a t h o d e a n d L i anode. S e l e c t e d e l e c t r o c h e m i c a l c h a r a c t e r i s t i c s o f a c e l l c o n s t r u c t e d from c i s _ - p o l y a c e t y l e n e f i l m ( t h i c k n e s s ~ 0.1mm; ~ 3.5mg/cm ) a n d l i t h i u m m e t a l immersed i n a n e l e c t r o l y t e o f 1.0M L i C l 0 4 i n t e t r a h y d r o f u r a n (THF) h a v e b e e n s t u d i e d . C e l l s were c o n s t r u c t e d i n a s i m i l a r manner t o t h o s e d i s c u s s e d i n t h e p r e c e e d i n g s e c t i o n ( 1 1 ) . A s p o n t a n e o u s e l e c t r o c h e m i c a l r e a c t i o n o c c u r s when t h e ( C H ) and L i e l e c t r o d e s a r e c o n n e c t e d by a w i r e e x t e r n a l t o t h e c e l l . The L i i s o x i d i z e d and t h e ( C H ) i s reduced d u r i n g t h e p r o c e s s a c c o r d i n g t o t h e r e a c t i o n s g i v e n below: Y

2

X

X

Anode R e a c t i o n

xyLi

Cathode R e a c t i o n

(CH)

xyLi

+

+ xye"

(2) y

X

+ x y e " *· ( C H ~ )

(3)

x

giving the o v e r a l l net reaction: xyLi + (CH)

X

+ [LiJ(CH-y)]

x

(4)

where y < 0.1. I t s h o u l d be n o t e d t h a t t h e r e a c t i o n g i v e n by E q u a t i o n 4 i s t h e d i s c h a r g e r e a c t i o n o f a v o l t a i c c e l l and t h a t t h e c e l l , i n i t s c o m p l e t e l y charged s t a t e c o n s i s t s o f p a r e n t , n e u t r a l ( C H ) w h i c h a p p e a r s t o be s t a b l e i n d e f i n i t e X


44.

pΑ: An Electrode-Active

KANER ET AL.

579

Material

l y i n the e l e c t r o l y t e . R e v e r s a l o f t h e r e a c t i o n g i v e n by E q u a t i o n 4 may be o b t a i n e d on c h a r g i n g a t a f i x e d a p p l i e d p o t e n t i a l o f 2.5V, the p o t e n t i a l ( v s . L i ) of the p a r e n t , n e u t r a l ( C H ) i n this electrolyte. A l t h o u g h r e d u c t i o n o c c u r s s p o n t a n e o u s l y , most s t u d i e s w e r e c a r r i e d out at constant a p p l i e d p o t e n t i a l s at v a r i o u s s e l e c t e d v a l u e s i n o r d e r t o s t u d y t h e s y s t e m i n a c o n t r o l l a b l e manner. S i g n i f i c a n t r e d u c t i o n of the ( C H ) occurs o n l y a t an a p p l i e d p o t e n t i a l l e s s t h a n 1.7V ( 1 0 ) . A f t e r the onset of r e d u c t i o n , the open c i r c u i t v o l t a g e , V , f a l l s r a p i d l y w i t h i n c r e a s i n g r e d u c t i o n up t o a r e d u c t i o n l e v e l o f ~ 1% a n d t h e n d e c r e a s e s more slowly. The r e l a t i o n s h i p between c e l l p o t e n t i a l a n d d e g r e e o f r e d u c t i o n h a s been s t u d i e d up t o 10% r e d u c t i o n l e v e l s . The r e d u c t i o n p r o c e s s was s t o p p e d a t i n t e r v a l s and t h e V v a l u e ( v s . L i ) was measured i m m e d i a t e l y . The c e l l was t h e n a l l o w e d t o s t a n d f o r a p e r i o d o f 24 h o u r s i n o r d e r t o p e r m i t p a r t i a l e q u i l i b r a t i o n o f t h e L i i o n s w i t h i n t h e ~ 200Â ( C H ) f i b r i l s . An i n c r e a s e i n p o t e n t i a l was o b s e r v e d on s t a n d i n g . T h i s i s c a u s e d by a d e c r e a s e i n t h e d e g r e e o f r e d u c t i o n on t h e o u t s i d e of t h e ( ~ ^ ) fibrils as t h e c o u n t e r L i i o n s d i f f u s e t o w a r d s t h e c e n t e r o f t h e f i b r i l s t o g e t h e r w i t h t h e i r a t t e n d a n t n e g a t i v e c h a r g e on t h e p o l y acetylene. E x a c t l y the opposite e f f e c t i s observed a f t e r a p a r t i a l e l e c t r o c h e m i c a l o x i d a t i o n (charge r e a c t i o n ) of ( C H ~ ) t o a l e s s reduced s t a t e . I n t h i s case, the V f a l l s on s t a n d i n g . X

X

o

c

o

+

c

X

C H

X

+

y

o

x

c

C o u l o m b i c e f f i c i e n c i e s , ( Q d i s c h a r g e / Q c h a r g e ^ ^ where ^discharge f s t o t h e t o t a l coulombs i n v o l v e d i n a g i v e n d i s c h a r g e ( r e d u c t i o n ) p r o c e s s and Q h a r g e r e f e r s t o t h e t o t a l c o u lombs i n v o l v e d i n a c h a r g e ( o x i d a t i o n ) p r o c e s s t o 2 . 5 V h a v e b e e n determined f o r s e v e r a l d i f f e r e n t l e v e l s of r e d u c t i o n . V a l u e s o f ~ 100% were f o u n d up t o 6% r e d u c t i o n l e v e l s . Somewhat s m a l l e r v a l u e s were f o u n d a t h i g h e r l e v e l s o f r e d u c t i o n . T h e s e h i g h c o u lombic e f f i c i e n c i e s are undoubtedly r e l a t e d , at l e a s t i n p a r t , t o the e x c e l l e n t c h e m i c a l s t a b i l i t y of the p a r t l y reduced p o l y acetylene i n the e l e c t r o l y t e . F o r e x a m p l e , s t u d i e s show t h a t the V o f a 7% r e d u c e d p o l y a c e t y l e n e e l e c t r o d e r e m a i n s r e m a r k a b l y c o n s t a n t a t ~ 1.05V f o r 40 d a y s as shown i n F i g u r e 1 ( l o w e r curve). When r e o x i d i z e d b a c k t o n e u t r a l ( C H ) t h e c e l l d i s p l a y e d a stable V o f ~ 2 . 0 4 V f o r a t l e a s t 40 days as shown i n F i g u r e 1 (upper c u r v e ) . S t u d i e s h a v e been made o f t h e change i n v o l t a g e d u r i n g c o n s t a n t c u r r e n t d i s c h a r g e s o f 0.1mA ( 1 9 . 8 A / k g ) , 0.5mA ( 9 8 . 8 A / k g ) a n d 1.0mA ( 1 9 7 . 6 A / k g ) t o 6% r e d u c t i o n o f t h e ( C H ) , i . e . , t o a c o m p o s i t i o n of [ L i g n f c i C H ) " " * ] i n each c a s e . The r e s u l t s a r e shown i n F i g u r e z . The w e i g h t o f t h e ( C H ) e m p l o y e d ( 4 . 9 m g , ~ 1 . 5 c m ) a n d t h e w e i g h t o f t h e L i consumed i n t h e d i s c h a r g e r e a c t i o n were u s e d t o c a l c u l a t e t h e n o r m a l i z e d d i s c h a r g e r a t e s i n Amps/kg g i v e n above. Even though each constant c u r r e n t d i s c h a r g e i n v o l v e d t h e same number of coulombs a n d h e n c e r e s u l t e d i n t h e same a v e r a g e p e r c e n t r e d u c t i o n , t h e f i n a l d i s c h a r g e v o l r

e

e

r

c

o

c

X

o

c

X

0

0 6

X

2


580


(CH)SvsLi V =2.04V

V =2.03V

oc

V = 2.03 V

V =2.04V

V =1.049 V

V = 1055V

oc

oc

oc

(CH)- vs.Li 007

V= 1.006V

V =Ί.040ν

oc

°0

5

10

15

20

TIME Figure

oc

oc

oc

25

30

35

40

(days)

1. Open c i r c u i t v o l t a g e , V Li/IM L i C l 0 , T H F / [ L i Q 4

o c

# 0 7

, v s . time c h a r a c t e r i s t i c s o f a (CH~

0 # 0 7

)]

χ

and o f a L i / I M L 1 C 1 0 4 , T H F / ( C H ) c e l l X

cell

(lower

(upper

curve),

curve).

3.0h 20 J * 0.1mA (19.8 Amps/kg)

i.o

ÊD-22.6W/kg

0

50

H370W-hr/kg

_L _l_ _L 100 150 200 250 300 350 MINUTES

3.0-

v

2.0-

l«0.5mA(98.8A/kg) PD-102.7 W/kg

d

1.0 H-1.0mA (197.6 A/kg) RQ«1923W/kg

10

20

E.D.124.6 W-hr/kg

30 40 50 MINUTES

60

70

F i g u r e 2. C o n s t a n t c u r r e n t d i s c h a r g e c h a r a c t e r i s t i c s o f a (CH) /1M L1C104, THF/Li c e l l . 4.9 mg o f ( C H ) was employed a s t h e cathode a c t i v e m a t e r i a l . X


X

44.


KANER ET A L .

581

Material

t a g e s , V , d e c r e a s e d as t h e d i s c h a r g e c u r r e n t s i n c r e a s e d , e . g . , V = 0 . 6 2 V a t 0.1mA, V = 0 . 5 2 V a t 0.5mA and V = 0 . 3 5 V a t 1.0mA. This i s due t o t h e f a c t t h a t t h e d i f f u s i o n e q u i l i b r i u m i n v o l v i n g m i g r a t i o n of the L i i o n s from the e x t e r i o r t o the i n t e r i o r of the ( C H ) f i b r i l s becomes l e s s c o m p l e t e t h e more r a p i d l y t h e e l e c t r o chemical reduction process i s c a r r i e d out. The e n e r g y d e n s i t y ( E . D . ) and a v e r a g e power d e n s i t y ( P . D . ) v a l u e s o b t a i n e d i n each of the above d i s c h a r g e s a r e , r e s p e c t i v e l y , 0.1mA, 1 3 7 . 0 W h r / k g and 2 2 . 6 W / k g ; 0.5mA, 1 2 4 . 6 W h r / k g and 1 0 2 . 7 W / k g ; 1.0mA, 1 1 6 . 8 W h r / k g and 1 9 2 . 3 W / k g . Maximum power d e n s i t y o f a L i / ( C H ) c e l l u s i n g 4 . 5 cm (~ 15mg) o f ( C H ) f i l m was o b t a i n e d by d i s c h a r g i n g i t t h r o u g h a n e x t e r n a l r e s i s t o r h a v i n g t h e same r e s i s t a n c e as t h e i n t e r n a l r e s i s t a n c e o f t h e c e l l (~ 15 o h m s ) . The c u r r e n t v s . t i m e d i s c h a r g e c h a r a c t e r i s t i c s a r e shown i n F i g u r e 3 ( c u r v e 1 ) . The c e l l was t h e n r e c h a r g e d i n a s e r i e s o f c o n s t a n t p o t e n t i a l c h a r g i n g s t e p s t o a f i n a l v o l t a g e of 2 . 5 V . The c o u l o m b i c e f f i c i e n c y was ~ 100%. Measurement o f t h e i n i t i a l c u r r e n t 54mA, F i g u r e 3 ( c u r v e 2) gave a maximum power d e n s i t y o f ~ 2 , 9 0 0 W / k g u s i n g t h e relationship P = I R where I = c u r r e n t at the b e g i n n i n g of the d i s c h a r g e . The c i r c u i t d i a g r a m i s a l s o shown i n F i g u r e 3 . Power d e n s i t i e s , c a l c u l a t e d u s i n g t h e same r e l a t i o n s h i p , a f t e r ~ 30 s e c o n d s a n d ~ 100 s e c o n d s o f d i s c h a r g e were 2 , 5 0 0 W / k g a n d l,200W/kg r e s p e c t i v e l y . A f t e r 1 m i n u t e t h e c u r r e n t was 45mA, a f t e r 2 . 5 m i n u t e s i t was 24mA a n d a f t e r 5 m i n u t e s i t had f a l l e n t o 14mA. The p r e s e n t s t u d i e s i n d i c a t e t h a t c e l l s i n v o l v i n g n e u t r a l a n d / o r p a r t l y r e d u c e d p o l y a c e t y l e n e h a v e e x c e l l e n t s t a b i l i t y and e x h i b i t i n t e r e s t i n g l y l a r g e e n e r g y and power d e n s i t i e s e v e n a t r e l a t i v e l y s m a l l l e v e l s of r e d u c t i o n of t h e p o l y a c e t y l e n e . d

d

d

d

+

X

X

2

m

m

Type I I : P o l y a c e t y l e n e C a t h o d e i n C o n j u n c t i o n w i t h a. P o l y a c e t y l e n e Anode: ( i ) n e u t r a l ( C H ) cathode + η-doped ( C H ) anode. S i n c e b o t h n e u t r a l and r e d u c e d ( C H ) h a v e good s t a b i l i t y i n a n e l e c t r o l y t e o f 1M L1C104 i n t e t r a h y d r o f u r a n a v o l t a i c c e l l c a n be c o n s t r u c t e d u s i n g ( C H ) as t h e c a t h o d e a n d ( ^) anode. D u r i n g d i s c h a r g e t h e ( C H ~ ^ ) g i v e s up a n e l e c t r o n t o the ( C H ) producing the net o v e r a l l r e a c t i o n : X

X

X

C H

x

X

a

s

t

n

e

X

X

[Li+(CH^)]

x

+ (CH) + 2 [ L i + x

/ 2

(CH-y/ )] 2

(5)

x

w h e r e L i a c t s as t h e c o u n t e r c a t i o n t o s t a b i l i z e t h e p o l y c a r banion species. A c e l l o f t h i s t y p e u s i n g 7% e l e c t r o c h e m i c a l l y r e d u c e d ( C H ) f o r t h e anode a n d n e u t r a l ( C H ) f o r t h e c a t h o d e h a s a n open c i r c u i t v o l t a g e , V , o f ~ 1.0V a n d a s h o r t c i r c u i t c u r r e n t , I , o f ~ 3mA/cm o f ( £ Η ) . The c e l l h a s e x c e l l e n t s t a b i l i t y ; d u r i n g a f i v e month p e r i o d i t s V remained constant a t 0 . 9 9 V as shown i n F i g u r e 4 . I t i s f u l l y rechargeable w i t h c o u l o m b i c e f f i c i e n c i e s o f ~ 100%. I t i s the f i r s t s t a b l e , r e c h a r g e a b l e b a t t e r y developed i n w h i c h b o t h the cathode and anode a c t i v e m a t e r i a l s a r e o r g a n i c p o l y m e r s . +

X

X

o

g

c

c

χ

o

c


582


60 50 40 30 I(mA) 20 10 "0

20

40

60

80

TIME Figure

3.

100

120

140

160

(sec)

C u r r e n t v s . time d i s c h a r g e t h r o u g h a matched l o a d r e s i s t o r f o r a L i / I M L i C I O , , THF/(CH) c e l l employ i n g 15 mg o f (CH) . The i n i t i a l c u r r e n t (54 mA) d u r i n g t h e s e c o n d d i s c h a r g e gave a maximum power d e n s i t y of 2900 W/Kg.

(CH)"?

2.0

0 7

vs.(CH)°

1.5 *oc

V =Q986V *—χ xI =5mA

V = 0.987V 1 O*-*—*• I =5mA

0C

0C

s c

s c

V = 0.992V •X f—X I =5mA oc

s c

0.5 _L 20

0

40

-L 60 TIME

Figure

4.

80

_L 100

_L 120

_L 140

(days)

Open c i r c u i t v o l t a g e , V ^ , a n d s h o r t g i g ^ u i t c u r r e n t , I , c h a r a c t e r i s t i c s of a [ L i (CH~ " )] / l i L i C 1 0 , THF/(CH) c e l l . °'° C

4

x

X


44.


KANER ET AL.

583

Material

( i i ) p-doped ( C H ) c a t h o d e + η-doped ( C H ) a n o d e . A number o f c e l l s o f t h i s t y p e have b e e n c o n s t r u c t e d by p l a c i n g two p i e c e s of ( C H ) f i l m ( a t t a c h e d m e c h a n i c a l l y t o P t o r N i w i r e ) i n an e l e c t r o l y t e c o n s i s t i n g o f ~ 1M L i C 1 0 o r ( B u N ) ( P F ) ~ d i s s o l v e d i n p r o p y l e n e c a r b o n a t e o r s u l f o l a n e . The e l e c t r o d e s a r e t h e n a t t a c h e d t o t h e p o s i t i v e and n e g a t i v e t e r m i n a l s r e s p e c t i v e l y of a ~ 2.5V d.c. power s o u r c e . The ( C H ) a t t a c h e d t o t h e p o s i t i v e t e r m i n a l i s o x i d i z e d and t h e ( C H ) a t t a c h e d t o t h e n e g a t i v e t e r m i n a l i s r e d u c e d t o t h e same e x t e n t . The o v e r a l l c h a r g i n g r e a c t i o n , e x e m p l i f i e d w i t h ( B u N ) ( P F ) ~ f o r 6% c h a r g i n g i s : Y

X

X

+

4

4

6

X

X

+

4

6

+

2(CH) +0.06x(Bu N) (PF )~ + x

4

W

[CH -

0 6

6

(PF )ô.o ]x [(Bu N)+ +

6

6

4

0 6

CH-°-

0 6

]

(6)

x

On c o n n e c t i n g t h e two t e r m i n a l s , t h e c e l l d i s c h a r g e s w i t h a r e v e r s a l o f t h e above r e a c t i o n . The b a s i c e l e c t r o c h e m i c a l r e a c t i o n during discharge i s : ( α ι

+0.06

) χ

+

( α Η

-0·06

) χ

> 2(CH)

(7)

X

C e l l s o f t h i s t y p e h a v e a n open c i r c u i t v o l t a g e o f ~ 2.4V f o r 6% d o p i n g and have a maximum s h o r t c i r c u i t d i s c h a r g e c u r r e n t o f ~ lOOmA/cm o f (CH) . They r e p r e s e n t t h e i d e a l t y p e o f a l l polymer c e l l s because of t h e i r r e l a t i v e l y l a r g e v o l t a g e , but t h e i r s h e l f l i f e i s n o t a s good a s t h e ( ΰ Η ~ ^ ) / ( Ο Η ) cells described before. The p r e s e n t r e s u l t s s u g g e s t t h a t e l e c t r o c h e m i c a l s t u d i e s n o t only of ( C H ) but a l s o of other conducting polymers represent an e x t e n s i v e area f o r f u r t h e r research not only of fundamental s c i e n t i f i c i n t e r e s t but a l s o of p o s s i b l e p o t e n t i a l t e c h n o l o g i c a l value· χ

χ

X

Acknowledgments The work i n v o l v i n g aqueous e l e c t r o c h e m i s t r y , ( R . J . M . ) , was s u p p o r t e d by t h e O f f i c e o f N a v a l R e s e a r c h and t h e D e f e n s e A d v a n c e d R e s e a r c h P r o j e c t s A g e n c y ( t h r o u g h a g r a n t m o n i t o r e d by t h e O f f i c e of Naval Research). S t u d i e s i n v o l v i n g nonaqueous r e c h a r g e a b l e b a t t e r i e s , ( R . B . K . ) , w e r e s u p p o r t e d by t h e D e p a r t m e n t o f E n e r g y , C o n t r a c t No. DE-AC02-81-ER10832. The a u t h o r s w i s h t o t h a n k D r . Mahmoud A l d i s s i and D r . MacRae M a x f i e l d f o r many helpful discussions.

Literature Cited 1. MacDiarmid, A. G.; Heeger, A. J. Synth. Met. 1979/80, 1, 101118.



584

2. Heeger, A. J.; MacDiarmid, A.G. i n "The Physics and Chemistry of Low Dimensional Solids"; Alcacer, L., Ed.; D. Reidel Pub lishing Co.: Dordrecht, Holland, 1979; pp. 353-391. 3. Etemad, S.; Heeger, A. J.; MacDiarmid, A. G. in "Annual Re view of Physical Chemistry"; Rabinovitch, B. S., Ed.; Annual Reviews, Inc.: Palo Alto, CA, 1982; Vol. 33, pp. 443-469. 4. Nigrey, P. J.; MacDiarmid, A.G.; Heeger, A. J. J. Chem. Soc., Chem. Commun. 1979, 594-5. 5. Guiseppi-Elie, Α.; Wnek, G. E. J.Chem. Soc., Chem. Comm. 1983, 63-65. 6. Su, W. P.; Schrieffer, J. R.; Heeger, A. J. Phys. Rev. Lett. 1979, 42, 1698-1701. 7. Su, W. P.; Schreiffer, J. R., Heeger, A. J.: Phys. Rev. B. 1980, 22, 2099-2111. 8. Nigrey, P. J.; MacInnes, D., J r . ; Nairns, D. P.; MacDiarmid, A. G.; Heeger, A. J. i n "Conducting Polymers"; Seymour, R. B., Ed.; Plenum: New York, 1981; pp. 227-233. 9. Nigrey, P. J.; MacInnes, D., J r . ; Nairns, D. P.; MacDiarmid, A. G.; Heeger, A. J. J. Electrochem. Soc. 1981, 128, 16511654. 10. Kaufman, J. H.; Kaufer, J. W.; Heeger, A. J.; Kaner, R. B . ; MacDiarmid, A. G. Phys. Rev. B. 1982, 26, 2327-2330. 11. Kaneto, K.; Maxfield, M.; Nairns, D. P.; MacDiarmid, A. G.; Heeger, A. J. J. Chem. Soc., Faraday Trans. I . , 1982, 78, 3417-3429. RECEIVED

September 2,

1983


An Electrode-Active Material in Aqueous and Nonaqueous Electrolytes

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