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

Abstract

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 Li2Mn3/4Cr1/4O2F (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.