Accessible Li Percolation and Extended Oxygen Oxidation Boundary in Rocksalt‐like Cathode Enabled by Initial Li‐deficient Nanostructure

Abstract

AbstractDisordered rocksalt cathodes have shown attractive electrochemical performance via oxygen redox, but are limited by a necessary Li‐excess level above the percolation threshold (x > 1.09 in LixTM2‐xO2, TM = transition metals) to obtain electrochemical activity. However, a relatively low‐Li content is essential to alleviate excessive oxygen charge compensation in rocksalt oxides. Herein, taking the homogeneous Li2MnO3 and LiMn2O4 as the starting point, disordered rocksalt‐like cathodes are prepared with initial Li‐deficient nanostructures, cation vacancies, and partial spinel‐type structures that provide a solution for the acquisition of fast Li+ percolation channels under Li‐deficient condition. As a result, the prepared sample exhibits high initial discharge capacity (363 mAh g−1) and energy density (1081 Wh kg−1). Advanced spectroscopy and in situ measurements observe highly reversible charge compensation during electrochemical process and assign coupled Mn‐ and O‐related redox contribution. Theoretical calculations also suggest the novel and chemical reversible trapped molecular O2 model in the rocksalt structure with vacancies, demonstrating a dual role of Li‐deficient structure in promoting cationic oxidation and extending reversible oxygen redox boundary. This work is expected to breakthrough the existing ideas of oxygen oxidation and opens up a higher degree of freedom in the design of disordered rocksalt structures.