ELECTROCHEMICAL SYNTHESIS OF COMPOSITE FILMS OF MANGANESE-DIOXIDE AND POLYPYRROLE AND THEIR PROPERTIES AS AN ACTIVE MATERIAL IN LITHIUM SECONDARY BATTERIES

Composite films of polypyrrole and beta-MnO2 or lithiated MnO2 (Li-MnO2) particles have been synthesized for use as cathode-active materials of rechargeable lithium batteries. The composite films were prepared by electrolysis of pyrrole dissolved in propylene carbonate solution in the presence of suspended MnO2 particles. The maximum amount of the incorporation of MnO2 was 50.2 and 40.6 weight percent for beta-MnO2 and Li-MnO2, respectively. It was found that both polypyrrole and the incorporated MnO2 worked as the active material with one potential plateau in the charge-discharge test conducted in a mixed solution of propylene carbonate and dimethoxyethane in which LiClO4 was dissolved. Furthermore, it was shown that polypyrrole worked as a conducting network for the incorporated MnO2. Though the utilization of the incorporated MnO2 was not high (beta-MnO2 and Li-MnO2 gave 0.23 and 0.57, respectively), the composite films prepared under optimal electrolysis conditions gave the specific energy density on volume basis of more than 150% of that obtained for a fully-utilized MnO2-free polypyrrole. Elemental analysis of the composite films revealed that electrolyte anions alone were involved in the redox reaction of polypyrrole of the composite films and Li+ ions in the redox reaction of the incorporated MnO2.