Synchronous phase transition and carbon coating on the surface of Li-rich layered oxide cathode materials for rechargeable Li-ion batteries

We describe a novel synchronous surface tailoring to form thin and uniform carbon coating layers and simultaneously induce an in-situ phase transition from a layered to spinel-like phase on the surfaces of Li-rich layered oxide (LLOs) particles by the thermal decomposition of 2,3-dihydroxynaphthalene (DN). The Li₂MnO₃ component in pristine LLO is not affected during carbon coating, but the coordination numbers of the Co ions and the Co–O bonds in the LiT_MO₂ phase are diminished during carbon coating, implying that the formation of a spinel-like phase in LLO after carbon coating begins at the LiT_MO₂ with little variation in the Li₂MnO₃. As a result, the optimized DN (0.2 wt%)-coated LLO cathode material shows superb electrochemical properties owing to the formation of uniform carbon coating layers and the layered-to spinel-phase transition on the surfaces of the LLO particles, which improves the surface stability, electronic conductivity, and Li-ion kinetics in the LLO.