Superstructure Reconstruction Stabilizes Anionic Redox in Cobalt-free Lithium-rich Layered Cathodes

Structural degradation in Li-rich manganese-based (LRM) 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 LiMn6 superstructure units in the Li2MnO3-like domains of Co-free Li1.2Ni0.2Mn0.6O2. Controlled re-sintering with KMnO4 treatment oxidizes a fraction of Ni2+ to Ni3+, which has a similar ionic radius with Mn4+, partially converting LiMn6 superstructure units into LiNiMn5 units. Guided by Pauling’s electrostatic valence principle, the LiNiMn5-containing motifs obtained through this Ni/Mn exchange mitigate the aggregation of LiMn6 units within the Li2MnO3-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 O2 release, thereby strengthening the layered framework's stability. As a result, the modified cathode (K-LRM) delivers 231 mAh g-1 at 0.1C and retains 83.8% of its capacity after 500 cycles at 1C, 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.