Decoupling Roles of Cationic Dimensionality and Valence‐Electron Compatibility on Structural Resilience and Kinetics in High‐Entropy Prussian Blue Cathodes for Sodium‐Ion Storage

Abstract High‐entropy Prussian blue analogues (PBAs) have considered as high‐performance cathodes for sodium‐ion batteries (SIBs). However, the impact of high‐entropy component compatibility on electrodes’ lattice stress and kinetics remains underexplored. Herein, a series of high‐entropy PBAs are served as cathode materials for SIBs. The tailoring Na2Mn0.2Fe0.2Co0.2Ni0.2Cu0.2[Fe(CN)6] (HE‐Cu) with superior mechanochemical compatibility shows superior phase stability without obvious lattice stress and faster electron/ion transfer kinetics. Intrinsic and accumulated lattice stresses can be obtained by ion‐incompatible Sn‐based high‐entropy PBA (HE‐Sn) and valence‐electron mismatched Ti‐based high‐entropy PBA (HE‐Ti), thereby exhibiting poor structure stability and dynamics. Serious Jahn–Teller structural distortion and unstable octahedron, observed in Na2Mn[Fe(CN)6] with complicated Na‐ion storage phase evolution (monoclinic ↔ cubic ↔ tetragonal), can be entirely suppressed by high‐entropy effect, appearing a zero‐strain solid‐solution reaction mechanism for HE‐Cu employing Mn, Fe, and Co‐ions as redox centers to involve in charge compensation. Consequently, HE‐Cu presents high initial specific capacity of 120.4 mAh·g−1, superior rate capability and outstanding cyclability with ultra‐long cycling life of 9000 cycles with the lowest capacity‐decay‐rate of 0.0042% per cycle. Na‐ion full cell demonstrates high initial energy density of 397.0 Wh·kg−1 and perfect cycling stability with long lifespan over 2000 cycles.