Exploring the mechanism of surface cationic vacancy induced high activity of metastable lattice oxygen in Li‐ and Mn‐rich cathode materials

Li‐ and Mn‐rich layered oxides exhibit high specific capacity due to the cationic and anionic reaction process during high‐voltage cycling (≥ 4.6 V). However, they face challenges such as low initial coulombic efficiency (~70%) and poor cycling stability. Here, we propose a combination of H3BO3 treatment and low temperature calcination to construct a shell with cationic vacancy on the surface of Li1.2Ni0.2Mn0.6O2 (LLNMO). The H3BO3 treatment produces cationic vacancy and lattice distortion, forming an oxidized On‐ (0<n<2) on the surface, accompanied by electrons redistribution. Low temperature calcination eliminates lattice distortion, activates metastable On‐ and promotes coherent lattice formation. In addition, the cationic vacancy shell reduces the diffusion energy barrier of Li+, allowing more Li+ and oxygen to participate in deeper reactions and increasing the oxidation depth of oxygen. The modified material (LLNMO‐H10‐200) exhibits an initial coulombic efficiency of up to 88% and a capacity of 256 mAh g‐1. Moreover, similar enhancements were observed with Co‐containing lithium‐rich materials, with a 280 mAh g‐1 discharge capacity and 89% coulombic efficiency. These findings reveal the correlation between cationic vacancy, metastable oxygen activation and bulk phase activity, offering a novel approach to enhancing the initial coulombic efficiency and cycle stability of Li‐rich materials.