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

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-FeS₂@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-FeS₂@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-FeS₂@C anode and Na₃V₂(PO₄)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.