Regulating oxygen covalent electron localization to enhance anionic redox reversibility of lithium-rich layered oxide cathodes

Abstract

Anionic redox and cationic redox chemistries enable Li-rich layered oxides to achieve ultrahigh specific capacities. Unfortunately, the irreversible nature of anionic redox participated by lattice oxygen causes the irreversible release of oxygen, leading to severe structural degradation and side reactions, which causes capacity/voltage fading. Herein, to solve the longstanding problem of anionic redox irreversibility, we propose a La/Al co-doping strategy involving the tuning of the fine electronic structures of a Co-free Li1.2Mn0.533Ni0.267O2 cathode, which consequently suppresses the release of lattice oxygen during cycling. We discover that the strong La-O and Al-O bonds weaken the covalency of TM-O bonds and promote covalent electron localization to oxygen, thereby facilitating Li+ migration and inhibiting the irreversible release of lattice oxygen. In addition, the induced layered-rocksalt heteroepitaxial interface effectively stabilizes the crystal structure and reduces side reactions at the electrode–electrolyte interface. As a result, the co-doped LMNLAO shows outstanding cycling stability with a capacity retention of 93.6% after 200 cycles and a least voltage attenuation of 1.35 mV/cycle significantly exceeding those of pristine LMNO. This strategy allows the regulation of the electronic structure to enhance the reversibility and reactivity of anion redox reactions, it can be applied for the development of other high-capacity cathodes.