Fe(7)Se(8) encapsulated in N-doped carbon nanofibers as a stable anode material for sodium ion batteries

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 Fe(7)Se(8) embedded in carbon nanofibers (denoted as Fe(7)Se(8)-NCFs). The Fe(7)Se(8)-NCFs with a 1D electron transfer network can facilitate Na(+) transportation to ensure fast reaction kinetics. Moreover, Fe(7)Se(8) encapsulated in carbon nanofibers, Fe(7)Se(8)-NCFs, can effectively adapt the volume variation to keep structural integrity during a continuous Na(+) insertion and extraction process. As a result, Fe(7)Se(8)-NCFs present improved rate performance and remarkable cycling stability for sodium storage. The Fe(7)Se(8)-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 Na(3)V(2)(PO(4))(3) to assemble full sodium ion batteries.