Achieving a bifunctional conformal coating on nickel-rich cathode LiNi_0.8Co_0.1Mn_0.1O₂ with half-cyclized polyacrylonitrile

Ni-rich cathode material is considered to be a promising cathode for commercial applications in lithium-ion batteries because of its low cost and high capacity. However, its chemical, electrochemical, and mechanical instability at the cathode-electrolyte interface cause a series of problems, such as inferior electrochemical performance and serious safety concerns. To construct a stable interface, we develop a simple and reproducible method to encapsulate LiNi_0.8Co_0.1Mn_0.1O₂ within ionic and electronic conductive half-cyclized polyacrylonitrile. The images of scanning electron microscopy and transmission electron microscopy prove that a continuous polymer layer formed on the surface of the cathode material. The organic coating layer is composed of both cyano groups that provide lithium-ion transport channels and cycled cyano groups that conduct electrons. At the same time, the elasticity of the coating polymer layer can maintain the mechanical stability of the cathode material during charge/discharge. Electrochemical studies demonstrate that the cycle and rate performances of LiNi_0.8Co_0.1Mn_0.1O₂ are obviously improved. After 100 cycles at a current density of 200 mA•g⁻¹, the capacity retention is increased from 83.93 to 96.24%. The design of this real conformal coating strategy provides a possible solution for the modification of other cathode materials.