Enhanced electrochemical performances of LiCoO2 cathode for all-solid-state lithium batteries by regulating crystallinity and composition of coating layer

Surface coating on the layered oxide is an effective method to improve its interfacial stability with sulfide electrolyte in all-solid-state lithium batteries. However, whether the formed coating layer is the designed one has been long ignored in the coating study. Here, representative layered oxide LiCoO2, coating layer LiNbO3 and sulfide electrolyte Li10GeP2S12 are selected to clarify this phenomenon. Specifically, LiNbO3 precursor is coated on the LiCoO2 surface and then calcined at different temperature to investigate the crystallinity and composition change of coating layer. It is found that the crystallinity and grain size of LiNbO3 coating layer are gradually improved with the increasing calcination temperature. Uniform LiNbO3 coating layer with better crystallinity and bigger grain size is formed after calcined at 600 degrees C, leading to the improved chemical and electrochemical stability between LiCoO2 and Li10GeP2S12, the excellent rate performance (105.5 mAh g(-1) at 1 degrees C) and ultrahigh cycle performance (78.0%@2000 cycles at 0.5 degrees C). As the calcination temperature further increases, a composite coating layer of Li3NbO4 and inactive Co3O4 is formed, leading to the composition change and electrochemical performance deterioration. This finding is of importance and can be applied to other layered oxide materials for sulfide-based all-solid-state lithium batteries.