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 Fe7X8@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 Fe7X8 nanoparticles from agglomeration and stabilize the interface of Fe/Na2X generated in the redox reactions. Fe7X8@C (X = S, Se) exhibits excellent reversible specific capacity (1005.3 mAh g-1 under 0.2 A g-1 for Fe7S8@C and 458.5 mAh g-1 under 0.5 A g-1 for Fe7Se8@C), outstanding rate performance (654.7 mAh g-1 for Fe7S8@C and 392.9 mAh g-1 for Fe7Se8@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 Fe7S8@C and 399.9 mAh g-1 going through 150 loops under 0.5 A g-1 for Fe7Se8@C). The excellent electrochemical performance of Fe7X8@C composites makes them promising anode materials for SIBs.