Constructing Iron Vacancies in Thiospinel FeIn2S4 to Modulate Fe D-Band Center and Accelerate Sodiation Kinetics Enabling High-Rate and Durable Sodium Storage

The bimetallic synergies effect and combined conversion/alloying mechanism endow thiospinel FeIn₂S₄ with great potential as an anode material for sodium-ion batteries (SIBs). However, their inconsistent synthesis, severe volumetric expansion, and sluggish reaction kinetics typically lead to unsatisfactory cyclic stability and rate capability. Herein, bimetallic organic framework derived FeIn₂S₄@N/S-C microrods with Fe vacancies is presented for fast, durable, and reversible sodium storage. The presence of Fe vacancies significantly modulates the d-band center of Fe and decreases the strength of the Fe─S bond for facilitating the sodiation reaction kinetics jointly. Moreover, a thin and stable solid electrolyte interface film with inorganic-rich components is formed by Fe vacancies induction. Combined with the N, S co-doped porous carbon matrix, the optimal sample delivers an excellent rate capability of 381 mAh g⁻¹ at 10 A g⁻¹ and a stable cyclic performance (448 mAh g⁻¹ after 500 cycles at 1 A g⁻¹). Furthermore, the assembled full-cells also exhibit superior electrochemical performance with 87.5% capacity retention after rate and long-term cyclic evaluations. This work presents a promising strategy for the structural regulation of bimetallic sulfides as advanced anodes for SIBs.