Fluorination‐Assisted Aqueous Quenching Chemistry Stabilizes Oxygen Redox in Li‐Rich Layered Oxides

ABSTRACT Li‐rich Mn‐based layered oxides (LRMs) are promising high‐energy cathode materials, but their practical application is hindered by the poor reversibility of oxygen redox. Highly reversible oxygen redox requires precise control over the initial defect chemistry established during synthesis. However, such control remains challenging because oxygen stoichiometry, defect formation, and structural ordering evolve concurrently during post‐calcination cooling. Here, we demonstrate that cooling‐induced oxygen chemistry critically governs local defect formation and cation rearrangement in LRMs and develop a fluorination‐assisted aqueous‐quenching strategy to regulate this process. This treatment effectively suppresses overoxidation‐driven cation‐vacancy generation, helps retain the local cation configuration established at high temperature, and mitigates cooling‐induced structural reorganization. Simultaneously, a fluorine‐rich passivation layer is constructed in situ on the material surface during quenching, which stabilizes interfacial oxygen chemistry and mitigates electrolyte side reactions. Benefiting from the synergistic regulation of the local bulk cation configuration and surface interfacial chemistry, the resulting fluorination‐assisted aqueous‐quenched cathode exhibits remarkably enhanced structural reversibility, suppressed voltage decay, and outstanding long‐term cycling stability. This work reveals the critical role of cooling‐induced defect chemistry and provides a bulk‐surface cooperative strategy for stabilizing high‐energy oxygen‐redox cathodes.