Regulating cation ordering in lithium-rich layered cathodes for enhanced anionic redox reactions

Abstract

Utilizing reversible lattice oxygen redox (OR) in battery electrodes is an essential strategy to overcome the capacity limitation set by conventional transition metal redox. However, these OR reactions frequently result in local structural changes, large voltage hysteresis, irreversible oxygen oxidation, and capacity decline. In this work, we provide a mechanistic insight into how the transition metal-Li (TM-Li) cation ordering affects the anionic redox performance. By developing two polymorphs of Li₂Ir_0.75Fe_0.25O₃ with different levels of TM-Li ordering, we demonstrate that the cation-disordered structure can enhance the transition metal-oxygen (TM-O) hybridization. In addition, the hybrid cation and anionic redox processes, with the complex intermediate (Ir^5.5 +-Fe⁴⁺-O^n-) formed at high voltages, demonstrate large capacity contribution and good reversibility. Our findings underscore the pivotal role of TM-Li ordering on OR activity and stability, which is vital for the development of high-capacity electrodes for Li-ion batteries.