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 1.2 Ni 0.2 Mn 0.6 O 2 surface to modulate the oxygen-oxidation end point from molecular O 2 to superoxide (O 2 – ). 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 O 2 into O 2 – 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.