What is the limiting factor of the cycle-life of Zn–polyaniline rechargeable batteries?

The factors affecting the cycle-life of Zn–polyaniline (PANI) rechargeable batteries are studied by means of electrochemical and surface analyses of electrodes. The PANI polymeric film is prepared by cyclic voltammetery in an aqueous solution, and is tested as the positive electrode (cathode) of a secondary battery containing a 1.0 M ZnCl2 and 0.5 M NH4Cl electrolyte. The battery is charged and discharged by a constant current. The capacity variation of Zn–PANI rechargeable batteries is studied as a function of cycle number, and the relation between capacity loss and performance of the zinc anode and polymeric cathode is examined. The behaviour of the zinc electrode is evaluated from Tafel plots. The capacity decreases with charge–discharge cycling. The cathode (PANI) is degraded electrochemically under charge conditions, and the cycle-life of the Zn–PANI rechargeable battery is limited by the anode (zinc). The polarization resistance (Rp) of the anode increases with cycling. As a result, the battery capacity is limited by the anode Rp. Surface analysis of the anode reveals that a solid phase containing the chlorine element is formed on the anode surface. The cycle-life of the Zn–PANI battery is limited by zinc passivation, which is possibly related to the formation of the solid phases ZnCl2·3NH4Cl and ZnCl2·2NH4Cl on the anode surface.