Study on the formation, development and coating mechanism of new phases on interface in LiNbO3-coated LiCoO2

Surface coating is one of important methods to improve the electrochemial performances of cathode material for Li-ion batteries. Few work focuses on whether the "the formed coating surface" is "the chosen coating surface" or not. In this study, it has been found that bulk material LiCoO2 (LCO) and the LiNbO3 coating material can react to produce Li3NbO4 and Co3O4 and form new coating layers during heating. The development of the new coating layers after calcination and their effect on the electrochemical performance of LiCoO2 have been thoroughly studied. Different types of coating layers (LiNbO3, LiNbO3/Li3NbO4/Co3O4, Li3NbO4/Co3O4 coating layers) were designed and obtained. The formation of new coating layer played a vital role in improving the electrochemical properties of coated materials. Coated LCO obtained at 650 oC with a LiNbO3/Li3NbO4/Co3O4 new coating layer exhibited the most excellent cycle stability with a capacity retention of 94.3% after 100 cycles at 0.2 C. The coating mechanism was studied. Both the composition and coating surface structure affect the performances of coated LCO. LiNbO3/Li3NbO4/Co3O4-coated LCO had the most uniform and integrated coating layer, maintained well crystal structure after long-term charging-discharging process. In addition, the LiNbO3/Li3NbO4/Co3O4 coating layer has been proved to inhibit the growth of cathode electrolyte interface.