Hydrothermal synthesis of carbon-coated LiCoPO4 cathode material from various Co sources

LiCoPO4 has been recognized as a promising cathode material for lithium batteries due to its high stability and high operation voltage. However, poor electronic conductivity of LiCoPO4 prohibits its practical use. A carbon coating can improve electronic conductivity of LiCoPO4. A hydrothermal synthesis is a very convenient method because it allows us easy preparation of small particles of carbon-coated LiCoPO4; however, an effect of precursor for LiCoPO4 preparation on the performance of the synthesized LiCoPO4 has yet to be cleared. In this paper, the effect of Co source for carbon-coated LiCoPO4 (LiCoPO4/C) preparation on performance as a cathode material for Li-ion battery is investigated. The Co source strongly affects the pH value in the starting solution and final products. The single-phase LiCoPO4 is obtained only when CoSO4 or CoCl2 are used as the Co sources. A quality of carbon layer on the LiCoPO4 is also affected by the Co source. The carbon layer on the LiCoPO4 synthesized from CoSO4 contains graphite carbon with high concentration which provides high electronic conductivity compared with that from CoCl2. Accordingly, the LiCoPO4/C synthesized from CoSO4 shows a superior performance than that from CoCl2 due to high-quality carbon layer.