Chemical preparation of manganese Dioxide Polypyrrole composites and their use as cathode active materials for rechargeable lithium batteries

Chemical preparation of composite powders of polypyrrole and either alpha-MnO2, beta-MnO2, or spinel LiMn2O4 has been successfully achieved by injecting Liquid pyrrole into an acidic medium containing suspended manganese dioxide powder as an oxidizing agent. The content of manganese dioxide in the composites increased with increasing amount of suspended manganese dioxide in the polymerization bath. The maximum content of manganese dioxide was 85, 87, and 83.3 weight percent for alpha-MnO2, beta-MnO2, and LiMn2O4, respectively. Charge-discharge tests of beta-MnO2/polypyrrole and LiNLn(2)O(4)/polypyrrole composites conducted in a mixed solvent of propylene carbonate and 1,2-dimethoxyethane (1:1) containing 1 mol dm(-3) LiClO4 have revealed that the polypyrrole worked well both as an active material and as a conducting network for manganese dioxide. The beta-MnO2/polypyrrole composite gave one potential plateau in both charge and discharge curves, whereas the LiMn2O4/polypyrrole composite exhibited two distinct potential regions. The utilization of manganese dioxide was higher when polypyrrole was used as the conducting matrix than when carbon powder was used. Elemental analyses of the composites have revealed that both electrolyte anions and cations were involved in the charge-discharge reaction of the beta-MnO2/polypyrrole composite, but electrolyte cations alone were involved in that of the LiMn2O4/polypyrrole composite. The mechanisms of the charge-discharge reaction of these two kinds of composites are in good conformity with the mechanism of composite formation.