ELECTROCHEMICAL OXIDATION AND REDUCTION OF POLYPARAPHENYLENE

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ELECTROCHEMICAL OXIDATION AND REDUCTION OF POLYPARAPHENYLENE

F. Maurice, G. Froyer, Y. Pelous

To cite this version:

F. Maurice, G. Froyer, Y. Pelous. ELECTROCHEMICAL OXIDATION AND REDUCTION OF POLYPARAPHENYLENE. Journal de Physique Colloques, 1983, 44 (C3), pp.C3-587-C3-590.

�10.1051/jphyscol:19833117�. �jpa-00222627�

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ELECTROCHEMICAL OXIDATION AND REDUCTION OF POLYPARAPHENYLENE

F. Maurice, G. F r o y e r and Y . P e l o u s

Centre NationaZ drEtudes des Te'Ze'comunications, LAB/ROC/TIC, B.P. 40, 22301 Lannion, France

Resume - Nous avons oxyd6 e t r e d u i t par Slectrochimie du polyparaphenylene (P.P.P.) s y n t h e t i s e sous forme de poudre ( 1 ) a p a r t i r du benzene. Grace a l a p o r o s i t e de l l @ l e c t r o d e de polym&re, c e l u i - c i put S t r e oxyde e t r e d u i t t r e s facilement malgre s a grande r e s i s t i v i t e i n i t i a l e . Nous avons observe de f o r t s courants de decharge, mais une e f f i c a c i t e coulombique 1 imi t e e . La d i f f e r e n c e e n t r e l e s p o t e n t i e 1 s . d e debut d'oxydation e t de reduction, de l ' o r d r e de 2,8 V , e s t plus f a i b l e que c e l l e rapportee j u s q u ' i c i ( 2 ) .

Abstract -

paraphenyl i n i t i a l l y t o a aood

We have s t u d i e d t h e electrochemical oxidation and reduction of poly- ene (P.P.P.) synthesized i n powder form from benzene ( 1 ) . A1 though i n s u l a t i n g , t h e polymer could be oxidized o r reduced very e a s i l y due p o r o s i t y of t h e m a t e r i a l . High discharge c u r r e n t s could be obtained, but with a l i m i t e d coulombic e f f i c i e n c y . The d i f f e r e n c e between t h e o n s e t vol- t a g e s of oxidation and reduction i s about 2.8 V , t h a t i s a lower value than t h a t previously reported ( 2 ) .

I - EXPERIMENTAL

P.P.P. has been prepared following t h e procedure described by Kovacic e t a1

.

^{( I ) ,}

which gives a brown powder.

Compact s e a l e d c e l l s were made as described in t h e l i t e r a t u r e f o r (CH), ( 3 ) , except t h a t t h e polymer e l e c t r o d e was made a s follows : P . P . P . was f i r s t annea,led a t 400°C before being pressed on a platinum mesh with a pressure over lo9 Pa. To anneal t h e powder i s believed t o c r o s s l i n k i t ( 4 ) and t o preserve a l a r g e s p e c i f i c a r e a throw$

compaction.

A l i s t i n g o f t h e c e l l c o n s t i t u e n t s and o f t h e open c i r c u i t voltages measured just a f t e r s e a l i n g i s given below :

I1 - RESULTS - DISCUSSION ID

A B.

C

a/ Doping i n i t i a t i o n

Although completely i n s u l a t i n g ( 5 ) , undoped P . P . P . could be electrochemically doped with f a i r l y high c u r r e n t d e n s i t i e s (up t o . 3 m~/cm2) without remarkable p o t e n t i a l

voc 3.47 V 3.20

v

2.85 V Sol vent

P.C.

T.H.F.

S a l t LiC104 Li PF6 LiC104

PPP weight 7 mg 17 mg 7 mg

Electrode a r e a 0.55 cm2 1.33 cm2 0.65 cm2

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19833117

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C3-588 JOURNAL DE PHYSIQUE

o v e r s h o o t : V i n i t i a l < 4.4 V f o r c e l l s A and B, P t y p e doping, and V i n i t i a l

> 0.94 f o r c e l l C, N t y p e doping.

b/ N t y p e d o p i n g - c e l l C

The r e d u c t i o n o f P.P.P. occurs t h r o u g h t h e r e a c t i o n :

F i g u r e 1 shows t h e V versus Q c u r v e r e c o r d e d d u r i n g an N t y p e doping-dedoping c y c l e .

2 2

F i g u r e 1

-

P.P.P. N t y p e doping. A : I = 1.5 mA/cm

.

^B: I = 0.75 mA/cm

.

C : V = 2 V f o r 12 h r s . The charge i s l a b e l l e d i n doping l e v e l p e r c e n t C6H4.

The r e d u c t i o n appears t o be e f f e c t i v e below 1 V. The coulombic e f f i c i e n c y f o r t h e whole c y c l e reaches 90 %.

c/ P t y p e doping

We performed b o t h c o n s t a n t c u r r e n t doping c y c l e s , s i m u l a t i n g b a t t e r y o p e r a t i o n , on c e l l s A and B, and q u a s i e q u i l i b r i u m s t u d i e s on c e l l B.

P t y p e doping would o c c u r t h r o u g h :

F i g u r e 2 shows t y p i c a l l a r g e c u r r e n t c y c l e s between 0 and 10 % d o p i n g l e v e l s . Oxi- d a t i o n b e g i n s above 4.2 V, -and t h e v o l t a g e r i s e s towards 4.5 V a t l o . % doping.

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Quasi e q u i l i b r i u m s t u d i e s o f P type doping were made on c e l l B. Doping c o n s i s t e d o f 500 sec. p e r i o d s w i t h a charging c u r r e n t of 10 ~ ~ / c m ~ i n alternance w i t h p e r i o d s o f 1000 sec. i n open c i r c u i t c o n d i t i o n s . Undoping used t h e same c o n d i t i o n s , b u t w i t h opposite c u r r e n t , and a l a r g e r recovery time (30 t o 90 mn). The doping l e v e l s were between 0 and 1 %.

4 .

3.-

2 -

The r e s u l t s are summarized i n f i g u r e 3.

a %

The important r e s u l t s are :

x Onset o f o x i d a t i o n a t about 3.8 V, i n s t e a d o f 4.4 V p r e v i o u s l y r e p o r t e d (2), reducing t h e d i f f e r e n c e between i o n i z a t i o n p o t e n t i a l and e l e c t r o n i c a f f i n i t y t o 2.8 V.

0 5 10 0 0.5 1

F i g u r e 2 - P type doping on c e l l A. F i g u r e 3 - Quasi e q u i l i b r i u m P type A : I = 0.36 m ~ / c m ~ . B1 : I = 1.8 m~/cm'. doping o f c e l l B. Envelops o f p o t e n t i a l B2 : I = 18 m~/cm2. extrema are given f o r I = 10 p ~ / c m ~ and

f o r I = 0.

The maximum coulombic e f f i c i e n c y i s 64 % f o r c e l l A, and 70 % f o r c e l l B. The leakage c u r r e n t s a c t t o lower the coulombic e f f i c i e n c y . They were measured f o r c e l l A i n steady s t a t e c o n d i t i o n s :

V = 4 . 3 V : I = 2 p A V = 4 . 4 V : I = 8 u A V = 4.5 V : I = 24 pA

They are assigned t o a p e r c h l o r a t e a t t a c k ( 6 ) and t h e b e t t e r e f f i c i e n c y o f c e l l B would be r e l a t e d t o a l a r g e r electrochemical window f o r LiPF6/PC than f o r

LiC104/PC ( 6 ) . Another consequence o f leakage c u r r e n t s i s t h a t the e f f i c i e n c y i s b e t t e r f o r f a s t doping c y c l e s than f o r slower ones.

The coulombic e f f i c i e n c y rose c y c l e a f t e r c y c l e a t the beginning, and two phenomena are b e l i e v e d t o occur d u r i n g the f i r s t c y c l e s :

- O x i d a t i o n o f i m p u r i t i e s .

-

C o n s t i t u t i o n o f permanently doped regions f a r from t h e c u r r e n t c o l l e c t o r , i s o l a t e d from i t d u r i n g t h e discharge.

High s h o r t c i r c u i t c u r r e n t d e n s i t i e s o f 85 m ~ / c m ~ were observed f o r c e l l A w i t h the polypropylene separator. This o r i g i n a t e s from t h e exceptionnaly l a r g e s p e c i f i c area o f t h e polymer e l e c t r o d e a1 ready discussed.

x Coulombic e f f i c i e n c y near 100 %. The c e l l v o l t a g e d i d nether exceed 4.2 V and the leakage c u r r e n t due t o the e l e c t r o l y t e degradation was n e g l i g i b l e .

m An h y s t e r e s i s i s observed i n the Voc curve, which m i g h t come from :

- K i n e t i c e f f e c t which leads t o under estimate t h e doping l e v e l on doping, and t o overestimate i t when undoping, t h e polymer j u s t i n c o n t a c t w i t h the p l a t i n u m mesh being f i r s t undoped, w i t h an associated increase i n t h e i n t e r n a l c e l l r e s i s t a n c e .

- E n t r o p i c e f f e c t associated w i t h i n t e r c a l a t i o n stages, r a t h e r u n l i k e l y below 1 % doping l e v e l

.

-

Electrons being taken from the valence band and r e i n j e c t e d a t a lower p o t e n t i a l i n a polaron band formed i n the gap w h i l e doping ( 7 ) .

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I 1 1 - CONCLUSION

Electrochemical c e l l s o f the type Li/LiA/(C H ) A = PF6, C104 have been made and have shown good N and P type doping a b i l i t i g s 4 d 6 e t o the l a r g e s p e c i f i c area o f the polymer e l e c t r o d e .

High o x i d a t i o n v o l t a g e and l a r g e s h o r t c i r c u i t discharge c u r r e n t s are t h e promising f e a t u r e s o f Polyparaphenylene f o r b a t t e r y appl i c a t i o n a1 though new e l e c t r o l y t e s should be employed i n o r d e r t o improve t h e r e v e r s i b i l i t y o f o x i d a t i o n .

Quasi e q u i l i b r i u m p t y p e doping s t u d i e s showed a good r e v e r s i b i l i t y associated w i t h an o x i d a t i o n v o l t a g e s t a r t i n g a t about 3.8 V versus L i . The d i f f e r e n c e w i t h t h e r e d u c t i o n s t a r t i n g v o l t a g e i s 2.8 V, and scales w i t h t h e forbidden energy gap o f P.P.P. We r e p o r t elsewhere ( 8 ) t h a t the onset o f t h e .rr +- .rr* o p t i c a l a b s o r p t i o n i n t h e U.V. range i s around 2.8 ev.

REFERENCES

(1) KOVACIC P., KYRIAKIS A., J. Am. Chem. Soc. 85(1963)454

(2) SHACKLETTE L.W., ELSENBAUMER R.L., CHANCE R.R., SOWA J.M., IVORY D.M., MILLER G.G., BAUGHMAN R.H., J . Chem. Soc., Chem. Commun.,(1982)361

(3) KANETO K., MAXFIELD M.R., NAIRNS D.P., MAC DIARMID A.G., HEEGER A.J. ; To be published i n J. Chem. Soc., Faraday t r a n s . I

(4) FROYER G., MAURICE F., MERCIER J.P., RIVIERE D., LE CUN M., AUVRAY P., Polymer 22(198 1)992

(5) MAURICE F., FROYER G., MINIER M., GAUNEAU M., J . Physique-Lettres 42(1981) L 425

( 6 ) COURTOT-COUPEZ J., L1HER M., Bul. Soc. Chim. de France 4(1970)1631 (7) BREDAS J.L., CHANCE R.R., SILBEY R., Phys. Rev. B, 26(1982)5843 (8) FROYER G., GOBLOT J.Y., GUILBERT J.L., MAURICE F., and PELOUS Y., T h i s

j o u r n a l , p o s t e r no 28 D, i n press (1983)