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

Core-shell type particles were prepared by reaction of LiMn2O4 powders in a n aqueous solution of pyrrole and paratoluene sulfonic acid. Thermogravimet ric analysis and X-ray diffraction studies of these organic-inorganic hybri d particles demonstrated that the polymerization of pyrrole was accompanied by delithiation of the starting spinel, manganese dissolution and creation of electrochemically inactive lambda-MnO2. This mechanism of polymerizatio n was confirmed by changing the experimental conditions, e.g., starting fro m lambda-MnO2 powders and using H2O-lithium paratoluene sulfonate medium. T he protective effect of PPy coating on the cyclability at 55 degrees C of t hese particles was studied in order to solve the well-known problem of capa city fading and self-discharge at elevated temperature of the LiMn2O4 spine ls. (C) 1999 Elsevier Science S.A. All rights reserved.