Characterization of Spinel Li_xCo₂O₄-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 LiCoO 2 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 Li x Co 2 O 4 . The slow quenching allows the two phases of LiCoO 2 and Li x Co 2 O 4 to intermix, whereas the post-thermal treatment at 800 °C results in the separation of the spinel phase at the surface of LiCoO 2 . 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 LiCoO 2 performs a role in enhancing the charge transfer activity of the active material.