Microstructural development and electrochemical characteristics of lithium cobalt oxide powders prepared by the water-in-oil emulsion process

Lithium cobalt oxide (LiCoO2) powders, utilized as cathode materials in lithium–ion secondary batteries, have been synthesized through the emulsion process. When the emulsion-derived precursors are calcined at elevated temperatures, the amounts of residual Co3O4 and organic species decrease and the crystallinity of LiCoO2 gradually improves with a rise in the calcination temperature. After calcination at 800 °C for 1 h, monophasic LiCoO2 powders with a R3m structure are successfully obtained. Compared to the traditional solid-state reaction, the emulsion process not only significantly curtails the reaction time to prepare LiCoO2, but also reduces the particle size. In the electrochemical test, both the specific discharge/charge capacity and the coulomb efficiency of LiCoO2 increase with a rise in the calcination temperature. Increasing the calcination temperature results in the formation of pure LiCoO2 without residual reactants, and also enhances the crystallinity of LiCoO2 as well as the ordering arrangement of lithium and cobalt cations in the layered structure, thereby facilitating the intercalation and deintercalation of lithium ions. As a result, the combination of the emulsion method with proper calcination processes is highly successful in producing LiCoO2 powders having large specific capacity and good cyclic stability along with high coulomb efficiency.