Unraveling the Roles of Self‐Converted Interphase and Capacity Sites in Facilitating High‐Flux Ion Transport for Prussian Blue Analogs Cathodes

Regulation of ion transport at the reaction interface of electrodes is essential for the design and development of high‐rate sodium‐ion batteries. Herein, a controlled self‐converted strategy is reported to construct iron oxides (Fe x O y ) ion‐regulated interphase on Fe‐based Prussian blue analogs (FePBAs) via a facile etching method in acetic acid media. Notably, this process simultaneously triggers an unexpected increase in sodium–ion storage sites within the bulk FePBAs. Uniquely, the designed Fe x O y interphase modulates the local solvation structure, restructures the Helmholtz layer, and thereby establishes a stable and uniform cathode‐electrolyte interphase to facilitate high‐flux ion transport. Meanwhile, increased sodium‐ions in the bulk phase will also boost ion transport flux by establishing a concentration gradient driving force between the electrolyte and the bulk lattice. The synergistic effect between Fe x O y interphase and increased bulk sites enhances ion transport kinetics through accelerated adsorption‐desolvation‐diffusion cascades, and finally achieves high‐flux ion transport (0.0854 mol m 2 h −1 ), superior to the pristine counterpart (0.0694 mol m −2 h −1 ). Consequently, the modified FePBAs cathodes exhibit exceptional rate capability and extraordinary long‐term cycling stability, retaining 80% capacity after 5000 cycles at 5 C. This work sets a new paradigm on interface/site engineering for the construction of high‐power energy storage systems.