Reversible Oxygen Redox in Li-Rich Mn Based Cathodes Achieved by Regulating the Local Environments of Bulk and...

Lattice-oxygen redox (L-OR) has been widely considered a viable approach to attain high-capacity cathodes for next-generation batteries. However, achieving highly reversible L - OR remains challenging due to the intrinsic chemical instability of lattice oxygen. As such, stabilizing the lattice oxygen becomes necessary for improving the performance of cathode materials with oxygen redox chemistry. In this study, the distinct properties of both bulk and surface lattice oxygen are systematically studied in a model Li-rich layered oxide material (LRMO, i.e., Li_1.2Ni_0.2Mn_0.6O₂) by employing different techniques. We find that, in the bulk, distortions in octahedral coordination geometry are closely correlated with variations in the electronic structure, and the substitution of Li ions with protons in a subsurface layer enhances the stability of surface lattice oxygen by altering its coordination environment. By jointly regulating the local environments of both bulk and surface lattice oxygen, the initial Coulombic efficiency is remarkably improved from 73.88% to 91.72%. Moreover, the modified LRMO demonstrates an impressive cycle stability, which realizes a capacity retention of 95.9% after 500 cycles at 250 mA g^-1. This work demonstrates that rationally-designed local environments of lattice oxygen can effectively stabilize the oxygen redox in Li-rich cathodes.