Abstract: LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) emerged as one of the crucial cathode materials in the field of power batteries owing to its high theoretical specific capacity. However, when the charging voltage exceeds 4.3 V, the material is prone to structural phase transitions and severe interfacial side reactions with the electrolyte, leading to increased interfacial impedance and rapid capacity fading, which restricts the further improvement of its energy density. In this study, a synergistic modification strategy is proposed: a synchronous lithiation process is adopted to prepare Mg-Cr co-doped LiNi_0.5Mn_1.5O₄ (LNMO) as the coating layer. This coating layer inherits the high operating voltage, three-dimensional lithium ion transport channels, and excellent electrochemical stability of LNMO. Meanwhile, Mg-Cr co-doping enhances the ionic/electronic conductivity of LNMO and inhibits the dissolution of Mn elements. The results demonstrate that the Mg-Cr co-doped LNMO coating modification reduces the degree of Li⁺/Ni²⁺ cation mixing in the NCM811 cathode material. The modified cathode material exhibits outstanding performance in the voltage range of 2.7-4.5 V. It delivers an initial discharge specific capacity of 212.74 mAh·g^-1 at 0.1C (1C=200 mA·g^-1), a discharge specific capacity of 182.32 mAh·g^-1 at a high rate of 5C, and a capacity retention rate of 77.09% after 100 cycles at 1C. Its electrochemical performance is significantly superior to that of the unmodified and stepwise-coated samples. This strategy improves the stability and electrochemical performance of NCM811 by suppressing interfacial side reactions and reducing charge transfer resistance, thereby providing an effective approach for the optimization of high-voltage and high-nickel cathodes.

Key words: NCM811, LNMO coating, Mg-Cr co-doping, synchronous lithiation