Modulating the surface ligand orientation for stabilized anionic redox in Li-rich oxide cathodes

Anionic redox chemistry is emerging as a key concept in the development of high-energy lithium-ion batteries, as it enables a nearly doubled charge storage capacity, aiding the development of high-capacity batteries. However, the anionic reactivity is frequently irreversible from charge to discharge, leading to rapid decay of the capacity and voltage of batteries over long-term cycling. Although the possibility of controlling the anionic redox reactions by tuning the geometric and electronic structures has recently been proposed, the implementation of this strategy is still a critical challenge. Herein, a strategy is proposed to improve the anionic redox reversibility of a model anionic redox active cathode material, Li${}_{1.2}$Ni${}_{0.13}$Co${}_{0.13}$Mn${}_{0.54}$O${}_2$, by tuning the surface ligand geometry via the growth of a lattice-compatible spinel LiCoO${}_2$ coating layer on the particle surface. Detailed local structure and first principles investigations reveal that the shape and orientation of the octahedral layer in the host lattice are modified. Accordingly, a two-band oxygen redox behavior is triggered in the ligand-orientation-regulated Li-rich cathode, leading to enhanced reversibility, and thus, remarkably improved capacity and voltage retention over cycling. This study highlights the importance of controllable ligand orientation, carving a new path for the development and design of Li-rich cathodes in the future. (© 2021 Wiley-VCH GmbH)