Reversible Mn/Cr dual redox in cation-disordered Li-excess cathode materials for stable lithium ion batteries

Cation-disordered Li-excess oxides/oxyfluorides have opened the door for designing alternative, high energy cathodes. However, achieving long cycle life and high rate capability represents a major challenge for disordered rocksalt cathodes (DRX). Herein, we develop Li2Mn3/4Cr1/4O2 F (LMCOF) DRX materials through a distinct redox mechanochemical method. The LMCOF contains trivalent Cr3+ and Mn3+, which allows for simultaneously accessing stable Mn/Cr dual redox at a narrow voltage window acceptable for conventional carbonate electrolytes. Coupled with the mitigated and reversible oxygen chemical changes, the LMCOF delivers high capacity, rate capability, as well as long cycle life upon extensive 1,000 cycles at various current densities. The multiscale synchrotron and neutron scattering, spectroscopic, and imaging analyses demonstrate that the capacity originates from the Mn/Cr dual redox with minimal contribution from oxygen redox, and that the good cycle life is attributed to the stable global crystal structure and local oxygen chemical environment. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

The development of Li2Mn3/4Cr1/4O2 F (LMCOF) DRX materials through a unique redox mechanochemical method allows for stable Mn/Cr dual redox performance at a narrow voltage window, resulting in high capacity, rate capability, and long cycle life. The stability of the global crystal structure and local oxygen chemical environment contribute to the good cycle life of the material, with minimal contribution from oxygen redox to the capacity.