Unveiling the Mechanism of High-Entropy Doping in Regulating Fe Spin State, Fe(CN) 6 4– Defects, and Fe–N Bond Strength in Fe-Based Prussian Blue Analogues for Sodium-Ion Batteries

Fe-based Prussian blue analogues (Fe-PBAs) possess a high specific capacity as cathode materials for sodium-ion batteries (SIBs), yet framework instability and inherent Fe(CN)64– defects significantly hamper their practical application. Here, we employ an innovative high-entropy doping strategy to overcome these limitations. By substantially boosting the material’s configurational entropy (to 1.73 R), we dramatically enhanced its electrochemical performance, achieving exceptional full-cell results: 88.8% capacity retention after 1000 cycles at 150 mA g–1. Mössbauer spectroscopy revealed that high-entropy doping effectively regulates the spin state of Fe. ICP-OES analysis confirmed that this strategy significantly reduces Fe(CN)64– defects within the material. In situ XRD demonstrated that the high-entropy structure mitigates volume strain during charging and discharging. Furthermore, density functional theory (DFT) calculations indicated that the high-entropy design strengthens Fe–N bonds and the rigidity of Fe–C bonds, thereby stabilizing the framework structure.