Fe7Se8 encapsulated in N-doped carbon nanofibers as a stable anode material for sodium ion batteries

Abstract

Transition metal chalcogenides especially Fe-based selenides for sodium storage have the advantages of high electric conductivity, low cost, abundant active sites, and high theoretical capacity. Herein, we proposed a facile synthesis of Fe₇Se₈ embedded in carbon nanofibers (denoted as Fe₇Se₈-NCFs). The Fe₇Se₈-NCFs with a 1D electron transfer network can facilitate Na⁺ transportation to ensure fast reaction kinetics. Moreover, Fe₇Se₈ encapsulated in carbon nanofibers, Fe₇Se₈-NCFs, can effectively adapt the volume variation to keep structural integrity during a continuous Na⁺ insertion and extraction process. As a result, Fe₇Se₈-NCFs present improved rate performance and remarkable cycling stability for sodium storage. The Fe₇Se₈-NCFs exhibit practical feasibility with a reasonable specific capacity of 109 mA h g⁻¹ after 200 cycles and a favorable rate capability of 136 mA h g⁻¹ at a high rate of 2 A g⁻¹ when coupled with Na₃V₂(PO₄)₃ to assemble full sodium ion batteries.