Electrochemical behaviour of LiMn2O4–PPy composite cathodes in the 4-V region

Core-shell type particles were prepared by reaction of LiMn2O4 powders in an aqueous solution of pyrrole and paratoluene sulfonic acid. Thermogravimetric analysis and X-ray diffraction studies of these organic–inorganic hybrid particles demonstrated that the polymerization of pyrrole was accompanied by delithiation of the starting spinel, manganese dissolution and creation of electrochemically inactive λ-MnO2. This mechanism of polymerization was confirmed by changing the experimental conditions, e.g., starting from λ-MnO2 powders and using H2O–lithium paratoluene sulfonate medium. The protective effect of PPy coating on the cyclability at 55°C of these particles was studied in order to solve the well-known problem of capacity fading and self-discharge at elevated temperature of the LiMn2O4 spinels.