In Situ Fabrication of Carbon-Encapsulated Fe₇X₈ (X = S, Se) for Enhanced Sodium Storage

Sodium-ion batteries (SIBs) have been regarded as a promising alternative to lithium-ion batteries due to the natural abundance of sodium in the earth’s crust. In our work, fusiform Fe 7 X 8 @C (X = S, Se) composites were obtained via a one-step pyrolysis strategy applied to SIB anode materials. The formed carbon skeleton could prevent the Fe 7 X 8 nanoparticles from agglomeration and stabilize the interface of Fe/Na 2 X generated in the redox reactions. Fe 7 X 8 @C (X = S, Se) exhibits excellent reversible specific capacity (1005.3 mAh g –1 under 0.2 A g –1 for Fe 7 S 8 @C and 458.5 mAh g –1 under 0.5 A g –1 for Fe 7 Se 8 @C), outstanding rate performance (654.7 mAh g –1 for Fe 7 S 8 @C and 392.9 mAh g –1 for Fe 7 Se 8 @C going through 300 loops even under 2 A g –1 ), and excellent cycling properties (795.8 mAh g –1 after 50 loops under 0.2 A g –1 for Fe7S 8 @C and 399.9 mAh g –1 going through 150 loops under 0.5 A g –1 for Fe 7 Se 8 @C). The excellent electrochemical performance of Fe 7 X 8 @C composites makes them promising anode materials for SIBs.