Exploring the Mechanism of Surface Cationic Vacancy Induces 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 Li_1.2Ni_0.2Mn_0.6O₂ (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.