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 PrMO_3-x layer on the Li_1.2Ni_0.2Mn_0.6O₂ surface to modulate the oxygen-oxidation end point from molecular O₂ to superoxide (O₂^-). Specifically, the PrMO_3-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 PrMO_3-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.