Enhancing Electrochemical Performance of LiMn2O4 Cathode Material at Elevated Temperature by Uniform Nanosized TiO2 Coating

摘要

The severe capacity fading of LiMn2O4 at elevated temperature hinders its wide application in lithium ion batteries despite several advantages over present cathode materials in terms of cost, rate capability, and environmental benignity. In this study, porous nanosized TiO2-coated LiMn2O4 is prepared via a modified sol gel process of controlling hydrolysis and condensation of titanium tetrabutoxide in ethanol/ammonia mixtures, and the phenomenon of homogeneous nucleation has been almost entirely avoided. The X-ray diffraction patterns and transmission electron microscopy images show that a porous nanosized TiO2 layer is uniformly coated on the surface of spinel LiMn2O4. Electrochemical tests reveal that the optimal coating content is 3 wt % which shows remarkably improved capacity retentions at both room temperature of 25 degrees C and elevated temperature of 55 degrees C. Even after long-term charge and discharge cycles, the TiO2 layer is still robust enough to prevent LiMn2O4 particles from the attack of electrolyte. The inductively coupled plasma-atomic emission spectrometry, electrochemical impedance spectroscopy, and X-ray photoelectron spectroscopy results indicate that the obvious improvement of TiO2-coated LiMn2O4 electrodes is attributed to the suppression of Mn dissolution, as well as the enhancement of kinetics of Li+ diffusion.