Pre‐Doping of Dual‐Functional Sodium to Weaken Fe─S Bond and Stabilize Interfacial Chemistry for High‐Rate Reversible Sodium Storage

Abstract Ferrous sulfides with the high theoretic capacity are the promising anode for sodium ion batteries. However, capacity fading and inferior rate capability still hinder their practical application. In this work, Na‐doped Fe 7 S 8 microrods with cationic vacancies and weakened Fe─S bond are constructed through a facile and scalable sulfurized route. The experimental results combined with theoretical analysis thoroughly reveal the generation of Fe vacancies and weakened Fe─S bond strength induced by sodium doping, which modulates the energy band structure of Na‐doped Fe 7 S 8 , provides more active sites, and accelerates the sodiation/desodiation reaction kinetics, simultaneously. Moreover, the pre‐doping sodium delivers a strong guiding effect on the formation of thin and stable solid electrolyte interface films. As the result, the optimal sample exhibits the excellent sodium storage performance, including the high and stable reversible capacity (674 mAh g −1 after 200 cycles at 0.5 A g −1 and 503 mAh g −1 after 1500 cycles at 10 A g −1 ), superior rate capability, and increased initial coulombic efficiency. Furthermore, the full cell paired with commercial Na 3 V 2 (PO 4 ) 3 also displays the outstanding cyclic stability with 95.9% capacity retention at 0.5 A g −1 after 100 cycles.