Unlocking Electrode Performance of Disordered Rocksalt Oxides Through Structural Defect Engineering and Surface Stabilization with Concentrated Electrolyte

Abstract Li‐excess cation‐disordered rocksalt oxides can boost the energy density of rechargeable batteries by using anionic redox, but the inferior reversibility of anionic redox hinders its use for practical applications. Herein, a binary system of Li 3 NbO 4 –LiMnO 2 is targeted and the systematic study on factors affecting electrode reversibility, i.e ., percolation probability, electronic conductivity, defect concentrations, and electrolyte solutions, is conducted. A Mn‐rich sample, Li 1.1 Nb 0.1 Mn 0.8 O 2 , delivers a smaller reversible capacity compared with a Li‐rich sample, Li 1.3 Nb 0.3 Mn 0.4 O 2 , because of the limitation of ionic migration associated with insufficient percolation probability for disordered oxides. Nevertheless, a larger reversible capacity of Li 1.3 Nb 0.3 Mn 0.4 O 2 originates from excessive activation of anionic redox, leading to the degradation of electrode reversibility. The superior performance of Li 1.1 Nb 0.1 Mn 0.8 O 2 , including Li ion migration kinetics and electronic transport properties, is unlocked by the enrichment of structural defects for nanosized oxides. Moreover, electrode reversibility is further improved by using a highly concentrated electrolyte solution with LiN(SO 2 F) 2 through the surface stabilization on high‐voltage exposure. Superior capacity retention, >100 cycles, is achieved for nanosized Li 1.1 Nb 0.1 Mn 0.8 O 2 . The electrolyte decomposition and surface stabilization mechanisms are also carefully examined, and it is revealed that the use of highly concentrated electrolyte solution can effectively prevent lattice oxygen being further oxidized and transition metal ion dissolution.