Surface and bulk composition of lithium manganese oxides

Lithium manganese oxides, and in particular the spinel-structured LiMn2O4, have been investigated as potential active cathode materials for lithium io n batteries, Recently both orthorhombic and monoclinic LiMnO2 have attracte d considerable attention. It has been reported that Al doping allows the pr eparation of monoclinic LiAlxMn1-xO2 under suitable reaction conditions, an d furthermore improves the capability retention of both o-LiAlxMn1-xO2 and m-LiAlxMn1-xO2. The aim of this study was to elucidate the structural effec ts of AI doping with particular attention to the surface properties of the material. X-ray diffraction data reveal that Al induces monoclinic stacking faults in orthorhombic LiAlxMn1-xO2 and at Al contents of similar to 5% th e preferred cation ordering becomes that of monoclinic LiAlxMn1-xO2. X-ray photoelectron spectroscopy measurements show that the AI is homogeneously i ncorporated throughout the grains up to its solubility limit, and no surfac e enrichment of AI is observed, The XPS data indicate that Mn in the near-s urface region of the material is predominantly present in its +3 oxidation state, even when annealed to temperatures of up to 250 degrees C, Copyright (C) 1999 John Wiley & Sons, Ltd.