P‐Band Center Engineering of Sulfur to Weaken Fe─S Bond Toward Superior Sodium‐Ion Storage

Abstract Iron‐based sulfides are appealing anodes of sodium‐ion batteries (SIBs) due to the high theoretical capacity, low‐cost, and excellent mechanical/thermal stability. However, achieving high electrochemical performances in such anodes is hindered by the strong Fe─S bonds and sluggish kinetics. Here, a unique carbon‐coated iron sulfide composite with abundant S vacancies (v‐FeS 2 @C) is designed, the spin polarization and S vacancy lift the p‐band center ( ɛ p ) of S and then decouple it from the d‐band center ( ɛ d ) of Fe, which weakens Fe─S bond and strengthens Na─S interaction. The obtained v‐FeS 2 @C anode exhibits ultrahigh rate capability of 438.0 mAh g −1 at 70 A g −1 and remarkable long‐life cycle performance (512.5 mAh g −1 after 8000 cycles at 40 A g −1 ). Particularly, the sodium‐ion full cell composed of v‐FeS 2 @C anode and Na 3 V 2 (PO 4 ) 3 cathode delivers the best specific capacity (211.5 mAh g −1 at 40 A g −1 ) and long cyclic stability (459.5 mAh g −1 after 2000 cycles at 5 A g −1 ). Such performances are much more superior to those of the other iron‐based sulfides. This work provides a new paradigm for boosting SIBs' performances of iron‐based sulfides by regulating p‐band center ( ɛ p ) of S and weakening Fe─S bonds.