Cation mixing effect regulation by niobium for high voltage single-crystalline nickel-rich cathodes

Single-crystalline nickel-rich layered NCM are promising candidate materials for advanced Li-ion batteries in long-range electric vehicles. However, several shortcomings must be overcome before full commercial utilization, including the lower specific capacity and poorer rate performance than polycrystalline layered cathodes, especially in the deep delithiation state. Herein, the Li⁺/Ni²⁺ cation mixing effect is strengthened by executing Nb-substitution to improve electrostatic interactions and electrochemical performances. Density functional theory calculation combined with in-situ experimental analysis are used to reveal the mechanism of Nb-substitution in regulating Li⁺/Ni²⁺ cation mixing effect. Stabilizing layered structure is intrinsically implemented through the regulation of Ni²⁺/Ni³⁺ ions. The Nb substitution is also found beneficial in enhancing the structural stability owing to the high bond energy of Nb-O. The optimal single-crystalline LiNi_0.79Nb_0.01Co_0.1Mn_0.1O₂ exhibits better electrochemical performances in terms of high discharge capacity (209.9 mAh g⁻¹) and high rate durability (91.4% retention after 100 cycles under 5 C). In sum, the proposed strategy looks promising for the design of high-performance cathodes, as well as the optimization of single-crystalline cathodes, promoting the application in high-energy–density batteries.