Effect of calcination temperature on the electrochemical behavior of ZnO-coated LiCoO2 cathode

Surface modification of LiCoO2 by metal oxides was verified to be an effective way to retard the abrupt capacity fading of LiCoO2 cycled at cut-off voltage higher than 4.2 V. In this study, LiCoO2 powders were coated with ZnO by the wet chemical method with a calcination process under various temperatures. Morphological and structural characterization of the bare and ZnO-coated LiCoO2 before and after cycling was carried out with field-emission scanning electron microscope (FE-SEM) and X-ray diffractometry (XRD). The electrochemical test results confirmed that ZnO coating was indeed a feasible approach to enhance the electrochemical performance of LiCoO2 at high voltage. The modified cathodes exhibited significantly improved capacity retention. In this material system, the optimal calcination temperature for ZnO-coated LiCoO2 is around 650 °C. Although the initial capacity of coated LiCoO2 derived at 650 °C was not the highest, its capacity retention was the most favorable. The mechanism of the cycleability improvement was proposed with respect to structural evolution, cation mixing degree, and the surface conditions.