THE AQUEOUS AND NON-AQUEOUS
ELECTROCHEMISTRY OF POLYACETYLENE :
APPLICATION IN HIGH POWER DENSITY
RECHARGEABLE BATTERIES
A. Macdiarmid, R. Kaner, R. Mammone, A. Heeger
To cite this version:
A. Macdiarmid, R. Kaner, R. Mammone, A. Heeger. THE AQUEOUS AND NON-AQUEOUS
ELECTROCHEMISTRY OF POLYACETYLENE : APPLICATION IN HIGH POWER DENSITY RECHARGEABLE BATTERIES. Journal de Physique Colloques, 1983, 44 (C3), pp.C3543-C3-550. <10.1051/jphyscol:19833109>. <jpa-00222618>
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https://hal.archives-ouvertes.fr/jpa-00222618
Submitted on 1 Jan 1983
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JOURNAL DE PHYSIQUE
Colloque C3, supplement au n06, Tome 44, juin 1983
page C3-543
THE AQUEOUS AND NON-AQUEOUS ELECTROCHEMISTRY OF POLYACETYLENE :
APPLICATION IN HIGH POWER DENSITY RECHARGEABLE BATTERIES
A. G. ~ a c ~ i a r m i ,
d *R.B.
~ a n e r *, R. J . Mammone* and A . J. ~ e e ~ e r ~
*Department of Chemistry, University of Pennsylvania, Philadelphia,
Pennsy Zvania 191 04, U. S. A.
""~epartmentof Physics, University of CaZifornia, Santa Barbara,
California 93106, U. S.A.
-
R6surn6
Le p o l y a c 6 t y l S n e p e u t G t r e d o p 6 p a r d e s moyens
c h i m i q u e s ou 6 l e c t r o c h i m i q u e s e n s o l u t i o n a q u e u s e j u s q u ' a u
regime m g t a l l i q u e . Les c a r a c t 6 r i s t i q u e s d e c e r t a i n e s b a t teries r e c h a r g e a b l e s s 6 l e c t i o n n 6 e s , q u i employent d e s 6 l e c t r o d e s d e (CH), d a n s d e s 6 l e c t r o l y t e s n o n - a q u e u x , s o n t
decrites.
A b s t r a c t - P o l y a c e t y l e n e c a n b e doped e i t h e r c h e m i c a l l y
o r e l e c t r o c h e m i c a l l y i n aqueous s o l u t i o n t o t h e m e t a l l i c
regime.
The c h a r a c t e r i s t i c s o f s e l e c t e d r e c h a r g e a b l e
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 i n non-aqueous
e l e c t r o l y t e s a r e described.
I
-
p-DOPING OF ( C H ) ,
I N AQUEOUS SOLUTION
I t is g e n e r a l l y b e l i e v e d t h a t p-doped ( C H I , r e a c t s r e a d i l y w i t h
water.
U n t i l 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 o n l y a p p a r e n t
exception t o t h i s water i n s t a b i l i t y involved t h e electrochemical
p-doping ( o x i d a t i o n ) o f ( C H ) , f i l m i n a n a q u e o u s 0 . 5 M s o l u t i o n
of K I .
Doping t o o k p l a c e i n a few m i n u t e s t o g i v e ( C H 1 0 . 0 7 ) ~
having 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 /I/.
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 n e e d e d f o r d o p i n g .
T h i s o b s e r v a t i o n was most s u r p r i s i n g .
The a b s e n c e o f r e a c t i o n
w i t h w a t e r would a t f i r s t s i g h t a p p e a r t o b e i n c o n s i s t e n t w i t h
is a polycarbonium
t h e f a c t t h a t p-doped ( C H ) x , i . e . , (CH'YA
i o n d e l o c a l i n e d w i t h i n s o l r t o n s and p o l a r g n i : f s i n c e
a l l other
carbonium i o n s r e a c t i n s t a n t l y w i t h n e u t r a l w a t e r and a r e s t a b l e
We
only i n c e r t a i n concentrated a c i d s o r "super-acid" s o l u t i o n s .
w i s h e d t o a s c e r t a i n w h e t h e r ( C H ) , doped w i t h i o d i n e was u n i q u e
o r w h e t h e r o t h e r d o p a n t s would b e h a v e s i m i l a r l y w i t h r e s p e c t t o
i t s r e l a t i v e s t a b i l i t y i n aqueous s o l u t i o n s .
-
cis (CH), f i l m a n d a p i e c e o f P t f o i l w e r e 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 of
0.5 M NaAsF6 i n 50% a q u e o u s HF.
The
(CH), 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 t t o t h e
n e g a t i v e e l e c t r o d e , r e s p e c t i v e l y , o f a d . c . power s u p p l y .
A
c o n s t a n t p o t e n t i a l o f 1.OV 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
c a . 30 m i n u t e s and t h e f i l m was t h e n washed i n 5 0 % HF and pumped
i n t h e vacuum s y s t e m f o r 18 h o u r s .
I n several d i f f e r e n t experiments, c a r r i e d o u t under 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 ,
A p i e c e ~f
E.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19833109
JOURNAL DE PHYSIQUE
C3-544
(z.
golden films having good metallic conductivity
10 to 100
ohm-lcm-l) were obtained. It was most surprising to find that
the films contained no oxygen. The fb;8s&ne content varied from
one preparation to another, e.g. [CH
( A ~ F ~ . ~ ) - (sum
~ . ~ ~ ~ ~ ~
[
c
H
+
~
'
~
~
~
of C + H + As + F analyses = 100.2%) and
(AsF4.7)-0.0291xr
(sum of C + H + As + F analyses = 100.3%). The nature of the
dopant species and the cause of the variable fluorine content is
currently being investigated. It is believed that the dopant
probably consists of a mixture of the (AsF6)- and (AsF4)- ions.
We have shown previously that (CH), can be doped readily to the
metallic regime when exposed to the vapor from 98% sulfuric acid or
72% perchloric acid /2/.
In view of the surprising electrochemical results obtained above, we wished to ascertain if (CH), could
be doped in aqueous solutions of these acids. We therefore
studied the (d.c.) conductivity of a strip of (CH), film immersed
in acid solutions of different strengths. At all concentrations
except the lowest, the conductivity of the partly doped (CH)x
was much greater than that of the ionic conductivity of the
solution. As can be seen from Fig. 1 and Fig. 2, the conductivity
of the (CA), increased rapidly at first and then increased only
very slowly for a period of s.24 hours, presumably due to slow
diffusion of the oxidizing acids into the interior of the (CH),
fibrils. The quasi-equilibrium conductivity values shown
18 Molar
-+
7
E,
-
1
15 Molar
0
12 Molar
-1
E
r: -2
0
-b
0
0
9 Molar
6 Molar
-3
-4
-5
TIME (rnln)
Fig. 1
-
Conductivity of &-(CH)x
film immersed in aqueous
sulfuric acid solutions of different concentrations.
in Fig. 1 and Fig. 2 are plotted in Fig. 3 and Fig. 4 as a function
of acid concentration (molarity). In each case, the conductivity
increases over five orders of magnitude to metallic levels! It is
most interesting to find that (CH)x can actually undergo a semiconductor-metal transition in aqueous solution and that the stability of the (cH+Y) ion to water is exceptionally great under
certain conditions. When the film doped in 18 M sulfuric acid
was washed with cyclohexene to remove free acid it was flexible
and golden and had a conductivity of 1 x 1 0 ~ohm-lcrn-l.
t3-
12 Molar
4-2-
--
4-1
-
9 Molar
0.
I
-g
IE
-1.
c
6 Molar
f
-2
3 Molar
2 -3
b -4
(3
3
-5
-6.
I
l
l
l
r
l
l
5
10 15 2 0 25 3 0
TIME (min)
Fig. 2
- Conductivity of *-(CH),
film immersed in aqueous
perchloric acid solutions of different concentrations.
1
2 4 6 8 10 12 14 16 18
MOLARITY OF
Fig. 3
- Relationship between quasi-equilibrium values of conductivity of cis-(CH)x film immersed in aqueous sulfuric
acid solutions of different concentrations.
JOURNAL DE PHYSIQUE
Fig. 4
-
Relationship between quasi-equilibrium values of confilm immersed in aqueous perductivity of *-(CH),
chloric acid solutions of different concentrations.
In view of the known oxid tion potentials (vs. Li/~i+) of
(CH),/(CH+~)~ , H2S03/S04-',
and C1-/ClO - which are -2. l V , -3.2V
and -4.36V, respectively, the expected ioping (oxidation) reactions which occurred are:
The greater the concentration of the acids, the greater will be the
to water
value of y in each case. The high stability of (cH'Y),
in certain cases is believed to be due to the extensive delocalization of charge which varies according to the nature of the dopant
anion associated with the (cH+Y) ion.
11
-
BATTERY CELLS USING (CH), AND/OR p-DOPED (CH),
(1) Neutral (CH)x cathode + Li anode: Selected electrochemical characteristics of a cell constructed from cis-polyacetylene film
0.lmm; ca. 3.5mg/cm2) and lithiup metal immersed in an
(thickness
in THF have been studied. A spontaneous
electrolyte of 1.OM Li=o4
electrochemical reaction occurs when the (CH), and Li electrodes are
connected by a wire external to the cell. The discharge reactions
are:
z.
x y ~ i ++ xye-
Anode Reaction
xyLi
Cathode Reaction
(CH), + xye-
+
(3)
+
(CH-Y),
(4)
+
Liy+ (CH-Y),
(5)
giving the overall net reaction
xyLi +
where y<0.1.
I t should be noted 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
( 5 ) is 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 c h a r g e d 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 (CH),
which a p p e a r s t o b e s t a b l e i n d e f i n i t e l y i n t h e e l e c t r o l y t e . ( S e e
F i g . 5 ) 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 b y e q u a t i o n ( 5 ) may b e o b t a i n e d o n 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, t h e p o t e n t i a l ( V S . L i ) o f t h e p a r e n t , n e u t r a l (CH), i n t h i s e l e c t r o l y t e .
5
Fig.
5
-
10
h.8~;;
15 20 25
TIME ( d a y s )
30
35
40-
Open c i r c u i t v o t
V , v a l u e s o f (CH), ( u p p e r c u r v e ) ,
( lower c u r v e ) , i n a 1 M LiC1o4
and t ~ i : 0 7 ( ~ ~ s o l u t i o n ' l n TRF.
T h e Vo
v a l u e f o r ( c H ) ~w a s d e t e r m i n e d
o n a p r v i o u s l y r e d u c e d E i l m which had t $ e n b e e n r e o x i d i z e d
t o (CHI,.
T h e s m a l l i n i t i a l d e c r e a s e i n Vo
is caused
b y d i f f u s i o n o f t r a c e s o f r e m a i n i n g d o p a n t Erom t h e
i n t e r i o r t o t h e e x t e r i o r o f t h e (CH), f i b r i l s .
,
8
Although 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 were c a r r i e d
o u t a t a constant applied potential a t various selected values jn
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.
Significant
r e d u c t i o n o f t h e (CH), o c c u r s o n l y a t a n 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.
A f t e r t h e o n s e t o f r e d u c t i o n , t h e o p e n c i r c u i t v o l t a g e , Vocr
f a l l s r a p i d l y 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 s l o w l y .
z.
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 and 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 a n d t h e Voc v a l u e ( v s . L i ) w a s m e a s u r e d immediately.
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 g 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 ~ i i' o n s w i t h i n t h e
200A (CH), f i b r i l s .
T h e Voc v a l u e s w e r e a g a i n r e c o r d e d .
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 o n s t a n d i n g .
T h i s is 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 o f t h e o u t s i d e o f t h e (cH-Y),
f i b r i l s a s the counter Lif ions d i f f u s e towards t h e center of a
f i b r i l 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 charge on t h e polyacetylene.
E x a c t l y t h e o p p o s i t e e f f e c t is observed a f t e r a p a r t i a l
t o a less
e l e c t r o c h e m i c a l o x i d a t i o n ( c h a r g e r e a c t i o n ) o f (CH-Y),
reduced s t a t e .
I n t h i s c a s e , t h e Voc f a l l s o n s t a n d i n g .
JOURNAL DE PHYSIQUE
C3-548
Coulombic efficiencies, (Qdischar e/Qcharge)fOO where (&ischar
e
refers to the total coulombs lnvoyved In a glven discharge (re%uction) process and Qcharge refers to the total coulombs involved in a
charge (oxidation) process to 2.5V have been determined for several
different levels of reduction. Values of 5. 99% were found up to
ca. 6.0% reduction levels. Somewhat poorer values were found at
higher levels of reduction. These high coulombic efficiencies are
undoubtedly related, at least in part, to the excellent chemical
stability of (CH), and partly reduced polyacetylene in the electrolyte as shown by Fig. 5.
Studies have been made of the change in voltage during constant current discharges of O.lmA (19.8Amps/Kg), 0.5mA (98.8Amps/Kg) and
l.OmA (197.6Amps/Kgl to 6.0% reduction of the (CH),, i.e., to a
composition of [Lin,06(~~)~.06]xin each case, (See Fig. 6).
ob o;
3.0
t
IAo tbo
2do 2
0
;
MINUTES
3b0 3&0
MINUTES
Fig. 6
-
Constant current discharge characteristics of a
(CH),/LiC104,(THF)/Li
cell.
The weight of the (CHI, employed (4.9mg) and the weight of the ti
consumed in the discharge reaction were used to calculate the normalized discharge rates in Amps/Kg given above. Even though each
constant current discharge involved the same number of coulombs and
hence resulted in the same average percent reduction, the final discharge voltages, Vd, decreased as the discharge currents increased,
e.g., Vd=0.62V at O.lmA, Vd=0.52V at 0.5mA and Vd=0.35V at l.0mA.
This is due to the fact that the diffusion equilibrium involving
migration of the ~ i +
ions from the exterior to the interior of the
(CH), fibrils becomes less complete the more rapidly the electrochemical reduction process is carried out.
The energy density and average power density values obtained in
each of the above discharges are, respectively, O.lmA, 137.0 Watt
hr/Kg and 22.6 Watts/Kg; 0.5mAt 124.6 Watt hr/Kg and 102.7Watts/Kg;
l.OmA, 116.8 Watt hr/Kg and 192.3 watts/Kg.
Maximum p o w e r d e n s i t y o f a c e l l u s i n g 4 . 5 cm2 (9
15mg)
. o f (CH),
f i l m w a s o b t a i n e d b y 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 resistor
h a v i n g t h e same r e s i s t a n c e a s 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
1 5 ohms), ( s e e F i g . 7 ) . Measurement o f t h e i n i t i a l c u r r e n t
(54mA) g a v e a maximum p o w e r d e n s i t y o f 2. 2 , 9 0 0 W a t t s / K g o n t h e
second d i s c h a r g e .
A f t e r 1 m i n u t e t h e c u r r e n t w a s 45mA, a f t e r 2 . 5
m i n u t e s i t w a s 24mA a n d a f t e r 5 m i n u t e s i t h a d f a l l e n t o 14mA.
Maximum p o w e r d e n s i t y v a l u e s a f t e r o t h e r d i s c h a r g i n g t i m e s a r e
given i n Fig. 7 .
(z.
Rz'LOAD RESISTANCE
1,-CURRENT
'0
Fig.
7
-
20
WHEN Ri- RJ
40 60 80 100 120 140
TIME (sec)
Maximum p o w e r d e n s i t y c h a r a c t e r i s t i c s o f a
(CH),/LiC104,
( T H F ) / L ~c e l l .
Curve 1 r e f e r s t o t h e
f i r s t discharge; curve 2 r e f e r s to t h e second discharge.
A coulombic e f f i c i e n t y o f 99% was o b t a i n e d on r e c h a r g i n g
a f t e r the f i r s t discharge.
( 2 ) N e u t r a l (CH), c a t h o d e + n-doped ( C H ) x a n o d e :
S i n c e b o t h neut r a l a n d r e d u c e d (CH), h a v e q o o d s t a b i l i t v i n a n e l e c t r o l v t e o f
I M LiC104 i n T H F a v o T t a i c c e l l w a s c o n s t P u c t e d u s i n g ( c H ~ a, s
t h e c a t h o d e a n d (CH-Y),
a s t h e anode.
The o v e r a l l d i s c h a r g e
r e a c t i o n is:
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 (CHIx f o r
t h e a n o d e a n d n e u t r a l (CH), f o r t h e c a t h o d e h a ? a p o t e n t i a l o f
1.OV a n d a s h o r t c i r c u i t c u r r e n t o f
3mA/cm o f (CH),.
The
c e l l s h o w s e x c e l l e n t s t a b i l i t y o v e r a 4-5 m o n t h p e r i o d .
(See
I t is f u l l y r e c h a r g e a b l e w i t h coulombic e f f i c i e n c i e s o f
F i g . 8).
ca. 99%. I t is t h e 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 d e v e l o p e d
i n which b o t h t h e c a t h o d e 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
polymers.
z.
z.
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 and/or
p a r t l y reduced p o l y a c e t y l e n e have e x c e l l e n t s t a b i l i t y and coulomhic
e f f i c i e n c y a n d some t y p e s 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 a n d
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 o f r e d u c t i o n o f t h e
polyacetylene.
JOURNAL DE PHYSIQUE
A'
io
l?b
$0 80
!do iho ido*
TIME (days)
Fig. 8
-
Open circuit voltage, Vocl and short circuit curren
characteristics of a ( C H ) ~ / L ~ C (TRF)/
~ O ~ , [ ~ i g (. ~C~ H
cell.
)I,~
REFERENCES
111 NIGREY, P.J., MACDIARMID,
Commun., (1979) 594.
[ 2 ] GAU, S.-G.,
A.G.
and HEEGER, A.J.,
J.C.S.
MILLIKEN, J., PRON, A., MACDIARMID, A.G.,
HEEGER, A.J., J.C.S. Chem.Commun., (1979) 662.
Chem.
and
ACKNOWLEDGMENTS
Studies involving aqueous chemistry and electrochemistry were supported by the Office of Naval Research and the Defense Advanced
Research Projects Agency (through a grant monitored by O.N.R.).
Studies involving polyacetylene batteries were supported by the
Department of Energy, Contract No. DE-AC02-81-ER10832.
~
!