Chemically sodiated iron disulfide as a high-capacity charge-storage host with cation- and anion-sited redox

Abstract

Alkali-rich iron disulfides (M₂FeS₂) are promising electrode materials for next-generation batteries owing to their high capacity and earth-abundant elemental composition. This work introduces a straightforward, low-temperature, and scalable chemical sodiation route to synthesize Na₂FeS₂ by reacting FeS₂ with a sodium-benzophenone adduct. Chemically sodiated Na₂FeS₂ has comparable charge-storage performance to materials produced using conventional high-temperature or electrochemical methods, exhibiting specific capacity >250 mAh g⁻¹ (1.55 e⁻ per formula unit). Spectroscopic analysis using X-ray emission spectroscopy (XES) and X-ray absorption near-edge structure (XANES) confirms the participation of both iron and sulfur redox during battery operation, demonstrating the contribution of anion redox to the high capacity of Na₂FeS₂ in nonaqueous electrolytes. Our results highlight the viability of chemical sodiation for the facile synthesis of Na₂FeS₂, enabling enhanced synthetic control and scalable production of this attractive battery material.