Tailoring Lattice Oxygen Redox and Robust Structure Stability in High-Entropy Superlattice Layered Cathode for Superior Potassium-Ion Storage

To address the inherent limitations of layered cathodes in terms of stability, kinetics, and energy density, a high-entropy superlattice layered oxide (K_0.7Mn_0.4Li_0.1Co_0.125Ni_0.125Fe_0.125Cu_0.125O₂, KMNCFCL_0.1) is proposed as a cathode for K-ion storage. High-entropy composition and [Li─O─K] configuration coupled with Cu─O covalency and local CuO₆ distortion trigger and stabilize lattice oxygen redox through the anionic–cationic redox inversion, essentially a premature ligand-to-metal charge transfer (LMCT), thereby alleviating potential issues of severe voltage hysteresis and capacity fade by restraining oxygen release and cation migration. Superior phase stability and strain tolerance with a solid-solution mechanism benefited from high-entropy stabilization, and “cocktail” effects can be successfully achieved by eliminating serious structural evolutions induced by Jahn–Teller (J–T) lattice distortion, O─O repulsion, and intercalation of electrolyte molecules. Furthermore, the enlarged interlayer spacing and disrupted K⁺/vacancy ordering facilitate rapid K-ion migration with a low diffusion barrier. Therefore, KMNCFCL_0.1 delivers a high energy density of 327.8 Wh kg⁻¹, superior cyclic stability with a long lifespan of over 300 cycles, and excellent rate capability. This research opens up new possibilities for achieving groundbreaking cathodic functionality in potassium layered oxides.