Characterization of Spinel LixCo2O4-Coated LiCoO2 Prepared with Post-Thermal Treatment as a Cathode Material for Lithium Ion Batteries

Both the origin and mechanism of the improvement in the electrochemical performances of post-thermal treated LiCoO2 as a cathode material for lithium ion batteries are investigated through high-quality characterization. X-ray diffraction and transmission electron microscopy measurements revealed that the high temperature sintering results in Li deficiency and the consequent formation of spinel LixCo2O4. The slow quenching allows the two phases of LiCoO2 and LixCo2O4 to intermix, whereas the post-thermal treatment at 800 °C results in the separation of the spinel phase at the surface of LiCoO2. The post-thermal treated material exhibits a much better cell performance for the cycling capacity and charge rate capability than the slowly quenched material. From the conductive atomic force microscopy measurement and electrochemical impedance spectroscopy experiment, it is shown that the high electrical conductivity of the effective coating layer of the post-thermal treated LiCoO2 performs a role in enhancing the charge transfer activity of the active material.