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 (KMnLiCoNiFeCuO, KMNCFCL) is proposed as a cathode for K-ion storage. High-entropy composition and [Li─O─K] configuration coupled with Cu─O covalency and local CuO 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 delivers a high energy density of 327.8 Wh kg, 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.