Regulating anionic redox reversibility in Li-rich layered cathodes via diffusion-induced entropy-assisted surface engineering

Cobalt-free lithium- and manganese-rich layered oxides (LMROs) are regarded as effective cathode materials for lithium storage due to their high capacity and cost-effectiveness. However, challenges with structural degradation, resulting in poor cyclability and rate performance, have hindered their widespread use. Essentially, rapid structural degradation arises from irreversible and complex redox reactions, triggering oxygen release, transition metal migration, and electrolyte decomposition. To tackle this issue, we propose an epitaxial entropy-assisted construction approach to develop a sturdy surface with adaptable composition, stabilising the surface crystal structure and preventing undesirable interface reactions. This distinct reconstructed surface comprises diverse heterogeneous elements and composite microstructures. The heteroatom-doped layer, with multi-doping sites like Li, O site, and tetrahedral positions, effectively manages the chemical environment and electronic structure of surface lattice oxygen. This epitaxial entropy stabilisation approach, stemming from multi-element synergy, effectively controls redox progress to limit oxygen release and curb transition metal migration, reducing structural decay. Additionally, the composite coated layer, containing oxygen defects and heterogeneous spinel phases, can hinder electrolyte corrosion and promote Li⁺ transport. Using these epitaxial entropy surface modifications, the LMRO cathode demonstrates regulated anionic redox reversibility and enhanced cycling stability across diverse operational conditions. This epitaxial entropy-assisted surface engineering offers a promising avenue for stabilising high-energy cathode materials.