Superstructure Reconstruction Stabilizes Anionic Redox in Cobalt‐Free Lithium‐Rich Layered Cathodes

Structural degradation in Li‐rich manganese‐based cathodes, driven by irreversible lattice‐oxygen loss and transition‐metal migration, remains a key obstacle to their practical deployment in high‐energy lithium‐ion batteries. Here, we report a facile oxidant‐driven strategy to reconstruct LiMn ₆ superstructure units in the Li ₂ MnO ₃ ‐like domains of Co‐free Li _1.2 Ni _0.2 Mn _0.6 O ₂ . Controlled re‐sintering with KMnO ₄ treatment oxidizes a fraction of Ni ²⁺ to Ni ³⁺ , which has a similar ionic radius to Mn ⁴⁺ , partially converting LiMn ₆ superstructure units into LiNiMn ₅ units. Guided by Pauling's electrostatic valence principle, the LiNiMn ₅ ‐containing motifs obtained through this Ni/Mn exchange mitigate the aggregation of LiMn ₆ units within the Li ₂ MnO ₃ ‐like domains. Concurrently, the treatment induces surface‐enriched oxygen vacancies. This synergistic effect of bulk superstructure dispersion and surface oxygen‐vacancy regulation enhances oxygen redox reversibility during cycling by suppressing O–O dimerization, transition metal migration, and irreversible molecular O ₂ release, thereby strengthening the layered framework's stability. As a result, the modified cathode (K‐LRM) delivers 231 mAh g ⁻¹ at 0.1 C and retains 83.8% of its capacity after 500 cycles at 1 C, with a reduced average voltage decay of 0.88 mV cycle ⁻¹ compared with 1.18 mV cycle ⁻¹ for the pristine LRM. This work demonstrates a simple and scalable route to tailor superstructure and anionic redox chemistry in Co‐free LRM cathodes, offering general guidelines for designing next‐generation high‐capacity and structurally stable layered oxides.