Performance variation of Li rechargeable cells having polypyrrole cathodes doped with different anions

Abstract

Electrochemically synthesized polymers such as polypyrrole (PPy), polyaniline (PANI) and polyNmethyl pyrrole (PNMP) are considered as one of the most promising polymer electrode material groups for the development of advanced electrochemical devices such as electrochemical cells, super capacitors, electrochromic devices and solar cells. The properties of electrochemically synthesized polymers are known to be largely dependent on the dopant anion used and hence, their performance in applications also depend greatly upon the dopants. In this study, the role of the anion used to dope the PPy cathode on the performance of a lithium (Li) rechargeable cell is reported. Anions were varied from small inorganic anions (CF3SO3 -) to large anions (alkilsulphonate, AS- and dodeclybenzenesulphonate, DBS-). PPy was electropolymerized and the cells were fabricated with a polyacrylonitrile (PAN) based solid polymer electrolyte (SPE) while Li served as the anode. Cyclic voltammetry and continuous charge discharge tests were carried out to characterize the cells. The cycling results showed better cycling charge and long cycle life with the cells fabricated with PPy doped with large anions. The cells with large anions showed higher cycle numbers while the cells with inorganic anions could not be cycled over 350 cycles. Even with electrodes having larger anions, better results can be obtained with slow scan rates. Scanning electron microscopy (SEM) studies revealed that electrodes have a porous morphology with smaller anions and a dense morphology with larger anions, which also affect the performance variations.