POLYMERS AND COPOLYMERS OF PYRROLE AND THIOPHENE AS ELECTRODES IN LITHIUM CELLS

The performance of pyrrole and thiophene polymer electrodes in lithium cells has been examined in the lithium perchlorate-propylene carbonat e electrolyte by cyclic voltammetry. Polypyrrole films were synthesize d in 'wet' and 'dry' conditions; pyrrole and thiophene copolymers were prepared at different potentials and bilayers were prepared by sequen tial deposition of polythiophene (PTh) and polypyrrole (PPy) films. Th e polymers were cycled between 2.0 V and 4.0 V in the lithium cells. T he effects of disconnecting the electrodes from the cell on the behavi our of the polymers regarding doping and coulombic efficiency were als o studied. The cycling performance of the 'wet' PPy is better than 'dr y' PPy, bilayer PTh/PPy and copolymers. No mixed behaviour was observe d for a bilayer where the inner layer was polythiophene and the outer layer was polypyrrol with a thickness PPy/Pth ratio equal to ten. The copolymer prepared at 3.9 V vs Li/Li+ showed the higher energy capacit y in Wh kg(-1) calculated from the anodic charge.