Abstract: LiNixCoyMnzO2 (NCM, x+y+z=1) is considered a promising cathode material due to its low cost and high energy density. However, with the increase of Ni content, the material will have serious Li/Ni mixing and interface side reactions, which will affect its stability. In this paper, LiNi0.90Co0.05Mn0.05O2 (NCM90), a high nickel cathode material, was coated with phosphotungstic acid (PTA) in different ratios by surface coating technology to explore the mechanism of improving its properties. Through the system characterization, electrochemical performance test and thermal safety test, it was found that PTA coating can promote Li+ diffusion and reduce electrochemical impedance, and form a WO3-Li3PO4 composite protective layer on the surface of the material, effectively isolating the side reaction between the cathode and the electrolyte, while maintaining the structural inte⁃grity of the material. Thus, the electrochemical performance and thermal stability of NCM90 are significantly improved. Among them, 0.5%PTA-NCM sample has the best performance, its specific discharge capacity is increased by 34.58 mAh/g compared with the original NCM, and the heat release is reduced by 194.56 J/g compared with the original NCM. In summary, PTA coating can effectively improve the electrochemical performance and thermal safety of NCM90. The research method and coating material may be applied to other high-nickel ternary cathode materials, which provides an important theoretical basis and practical guidance for the optimization of cathode properties.

Key words: lithium-ion batteries, surface coating, high nickel ternary cathode, thermal stability, electrochemical performance