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

Disordered 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 O-2 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.

Automated summary

Disordered rocksalt-like cathodes with initial Li-deficient nanostructures, cation vacancies, and partial spinel-type structures have been prepared, providing fast Li+ percolation channels under Li-deficient condition. The prepared sample exhibits high initial discharge capacity and energy density. Advanced spectroscopy and in situ measurements observe highly reversible charge compensation and assign coupled Mn- and O-related redox contribution. Theoretical calculations suggest a novel and chemical reversible trapped molecular O-2 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 break through the existing ideas of oxygen oxidation and opens up a higher degree of freedom in the design of disordered rocksalt structures.