Removing the Intrinsic NiO Phase and Residual Lithium for High-Performance Nickel-Rich Materials

Layered Ni-rich materials for lithium-ion batteries exhibit high discharge capacities but degraded cyclability at the same time. The limited cycling stability originates from many aspects. One of the critical factors is the intrinsic insulating residual lithium compounds and the rock-salt (NiO) phase on the surface of particles. In this work, LiNi_0.8Co_0.1Mn_0.1O₂ material is etched with a trace amount of boric acid and used as a model to demonstrate the influences of weak acid treatment on the surface phase regulations. After the etching process, the pH of the material is reduced from 12.08 to 11.82, along with a lower cation mixing degree and promoting electrochemical performances. Corresponding measurements demonstrate that weak acids such as H₃BO₃ can also etch the NiO phase on the surface to adjust the surface of the particles to a pure layered structure. This process improves the lithium-ion diffusion and electron transport in the interface between material and electrolyte, consequently leading to better cycling performance and rate capability. This study provides a novel strategy and comprehensive understanding of acid modification and surface phase regulation process of Ni-rich cathode materials for lithium-ion batteries.