Improved electrochemical performances of surface-modified spinel LiMn2O4 for long cycle life lithium-ion batteries

The surface of spinel LiMn2O4 was modified with inorganic salt LiAlO2 by a sol-gel method to improve its electrochemical performance at elevated temperatures. Compared with pristine spinel LiMn2O4, surface-modification improved the cycling stability of the material at elevated temperatures. The capacity retention of LiAlO2-modified spinel LiMn2O4 was more than 94% after 500 cycles at room temperature and more than 90% after 200 cycles at 55degreesC at 1C charge-discharge rate. Thermogravimetry/ differential scanning calorimetry studies showed that the formation process of LiAlO2 on LiMn2O4 was different from that of pure LiAlO2. Powder X-ray diffraction indicated that spinel was the only detected phase in LiAlO2-modified LiMn2O4. X-ray photoelectron spectroscopy showed that the Al content in the spinel decreased with the detection depth beneath the particle surface of the sample. Introduction of Al and Li into LiMn2O4 changed the electronic structures of its O and Mn atoms on the particle surface, but the electronic structure of Al remained unchanged. Therefore a surface solid solution of LiAlxMn2-xO4 was formed on LiMn2O4. The thickness of the surface solid solution LiAlxMn2-xO4 was estimated to be about 12 nm. The improved electrochemical performance of surface-modified spinel LiMn2O4 was attributed to the protection effect of the surface solid solution shell while the improved stability of crystalline structure was assigned to the entrance of Li+ and Al3+ into the spinel crystalline structure. (C) 2003 The Electrochemical Society.