Reconstructed Perovskite Layers Regulate Surface-Oxygen Dimerization States Enabling Reversible Anionic Redox in Li-Rich Layered Oxides

Li-rich layered oxides are regarded as promising next-generation cathodes because their additional oxygen redox enables ultrahigh capacities (>250 mAh g–1). However, the irreversibility of oxygen redox triggers oxygen loss and structural degradation during cycling, resulting in severe voltage decay and capacity loss. To address this issue, we introduce a perovskite-type PrMO3–x layer on the Li1.2Ni0.2Mn0.6O2 surface to modulate the oxygen-oxidation end point from molecular O2 to superoxide (O2–). Specifically, the PrMO3–x layer traps migrating O–O dimers via intrinsic O vacancies and promotes electron donation from adjacent Mn cations, thereby reducing the escaping O2 into O2– species. This suppresses excessive oxygen oxidation and significantly improves the reversibility and kinetics of oxygen redox. Functioning as such a passivating interphase, the PrMO3–x layer markedly stabilizes the cathode surface over prolonged cycling, inhibiting the layered-to-spinel/rock-salt phase transition and fostering a robust cathode–electrolyte interphase (CEI). Consequently, the modified PrMO@LRNM cathodes achieve 93% capacity retention with only 1.4 mV per cycle voltage decay. This perovskite-coating strategy is readily extendable to other high-voltage, Co-lean/free cathodes.