Research Progress on Surface Coating Layers on the Positive Electrode for Lithium Ion Batteries

Lithium ion batteries (LIBs) are one of the most promising secondary batteries due to their advantages including long cycle life, high energy density, limited self-discharge, high operating voltage and environmental friendliness. The development of electrode materials is crucial for the further application of LIBs. There are many effective ways to enhance the performance of positive electrode materials of LIBs such as surface coating, ion doping, preparation of composite materials and nanosized materials and so forth. Among them, surface coating is considered to be a promising way to improve the electrochemical performance of LIBs. Surface coating can normally form a physical barrier or a doped surface layer to play favorable roles for the electrode materials, such as hindering side reactions between positive electrode materials and the electrolyte. In this paper, different kinds of surface coating layers will be discussed according to previous research, including carbon materials, metal oxides, metal fluorides, metal phosphates, nonmetal oxides, electrode materials coating layer, hybrid coating layer, polymer and so forth. In addition, the mechanism of these coating materials will be summarized, and the future development will be discussed in this paper.