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 O2 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 Li1.225Ti0.45Mn0.325O1.9Cl0.1 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 O2- 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 Li1.225Ti0.45Mn0.325O1.9Cl0.1 cathode exhibits significantly improved cycling durability at high current densities, compared with the pristine Li1.225Ti0.45Mn0.325O2 cathode. This work demonstrates the promising feasibility of the Cl substitution process for advanced cation-disordered rock-salt cathode materials.