Regulating the Anion Redox and Suppressing the Structural Distortion of Cation-Disordered Rock-Salt Cathode Materials to Improve Cycling Durability through Chlorine Substitution

Abstract

Owing to the capacity boost from anion redox activities, cation-disordered rock-salt oxides are considered as potential candidates for the next-generation of high energy density Li-ion cathode materials. Unfortunately, the anion redox process that affords ultra-high specific capacity often triggers irreversible O 2 release, which brings about structural degradation and rapid capacity decay. In this study, we present a partial chlorine (Cl) substitution strategy to synthesize a new cation-disordered rock-salt compound of Li 1.225 Ti 0.45 Mn 0.325 O 1.9 Cl 0.1 and investigate the impact of Cl substitution on the oxygen redox process and the structural stability of cation-disordered rock-salt cathodes. We find that partial replacement of O 2− by Cl − expands the cell volume and promotes anion redox reaction reversibility, thus increasing the Li + ion diffusion rate and suppressing irreversible lattice oxygen loss. As a result, the Li 1.225 Ti 0.45 Mn 0.325 O 1.9 Cl 0.1 cathode exhibits significantly improved cycling durability at high current densities, compared with the pristine Li 1.225 Ti 0.45 Mn 0.325 O 2 cathode. This work demonstrates the promising feasibility of the Cl substitution process for advanced cation-disordered rock-salt cathode materials.