Ion-Exchange: A Promising Strategy to Design Li-Rich and Li-Excess Layered Cathode Materials for Li-Ion Batteries

Li-rich and Li-excess oxides have been regarded as a promising category of cathode materials for next-generation Li-ion batteries due to their high energy density on basis of anionic/cationic redox chemistry. However, the application of Li-excess oxides suffers from significant problems, such as irreversible lattice oxygen loss and structural distortion. A Li/Na-ion exchange strategy can be regarded as an effective way to address these obstacles by tuning oxygen stacking arrangements and the coordination environment of alkali metal within emerging structures. Herein, the state-of-the-art progress made within conventional and Li-excess layered cathodes generated by ion exchange strategy at first is reviewed. Moreover, the mechanisms of oxygen redox, the migrations of Li/transition metals, and structural evolutions within Li-excess oxides have been further clarified by advanced characterizations, which play an important role in understanding lattice oxygen release, irreversible transition metal migration, phase transition, and the root of capacity/voltage decay. In addition, the theory calculations based on density of states, oxygen release energy, and migration energy barriers of Li/transition metals are systematically summarized, providing an essential guidance to harvest stable oxygen-related redox reactions within Li-excess materials. Altogether, this review offers fundamental understanding and future perspectives toward the rational design of high-energy-density Li-excess oxides with reversible anionic/cationic redox chemistry.

Automated summary

This study reviews the potential application of Li-rich and Li-excess oxides as cathode materials for next-generation Li-ion batteries, discusses the challenges in using Li-excess oxides, and explores mechanisms to address these issues. Future research directions in the field are also proposed based on advanced characterizations and theory calculations.