Electrochemical Characterization of Surface-modified LiMn_2O_4 Cathode Materials for Li-ion Batteries

摘要

To improve the performance, the surface of LiMn_2O_4 was coated with very fine MgO, Al_2O_3 and ZnO fry sol-gel method, respectively. The structure and morphology of the coated materials were investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy ( XPS) and scanning electron microscopy ( SEM). The charge and discharge performance of uncoated and surface modified LiMn_2O_4 spinel at 25 deg C and 55 deg C were tested, using a voltage window of 3.0-4.35 V and a current density of 0.1 C rate. There is a slight decrease in the initial discharge capacity relative to that of uncoated LiMn_2O_4, but. the cycle ability of Li LiMn_2O_4 coated by metal-oxide has remarkably been improved. The EIS measurements of uncoated and Al_2O_3-coated LiMn_2O_4 were carried out by a model 273 A potentiostat/galvanistat controlled by a computer using M270 software, and using a frequency response analyzer ( Zsimpwin) combined with a potentiostate ( PAR 273). Consequently, the reason for the improved cycle properties is that the surface modification reduces the dissolution of Mn, which results from the suppression of the electrolyte decomposition, and suppresses the formation of passivation film that acts as an electronic insulating layer. In conclusion, the use of surf ace modification is an effective way to improve the electrochemical performance of LiMn_2O_4 cathode material for lithium batteries.