Vacancy‐Repairing Facilitated Tilt/Dilation Dual‐Mode Lattice Flexibility for High‐Rate Prussian Blue

Abstract Prussian blue (PB) is a promising high‐rate cathode material of sodium‐ion batteries (SIBs) for its 3D Na⁺ diffusion pathways, yet its power output is hindered with the inevitable Fe(CN) 6 vacancies in as‐prepared PB. A mild Na‐compensation strategy is hereby reported that simultaneously repairs the vacancies and preserves a near‐cubic framework. Synchrotron X‐ray diffraction showed that the lattice of the repaired PB (rPB) is a more flexible and follows dual modes of strain upon Na + extraction and insertion, rhombohedral tilting below 3.3 V and nearly isotropic dilation (reverse expansion) above 3.3 V, facilitating the Na + transport. The drop of the specific capacity of rPB is only 3.2% as the current density rose from 50 to 5000 mA g −1 . The energy density of rPB reaches 253.4 Wh kg −1 at 5000 mA g −1 . These findings provide a mild, scalable route toward preparing high‐power‐density SIB cathode materials and clarify the positive role of moderate lattice distortion.