WSe2/CoSe2 nanocrystals in situ growth on three-dimensional carbon nanofibers as anode material for long-life and high-rate sodium-ion batteries

Transition metal selenides are regarded as one of the most promising anode materials because of their high theoretical specific capacity and large layer spacing. However, the unstable structural behavior and slow reaction kinetics during electrochemical reactions seriously hinder its application. Herein, a novel nanocomposite structure of WSe2/CoSe2 nanocrystals vertically grown on carbon nanofibers (WSe2/CoSe2/CNFs) was developed as anode material by electrospinning and heat treatment. In which, the self-supporting structures formed by the intersecting carbon nanofibers effectively alleviate severe volume expansion during sodiation/desodiation process, thus ensuring excellent stability. And the highly exposed CoSe2/WSe2 grown on the surface of carbon nanofibers provide abundant reaction interfaces and fast ion diffusion channels. As expected, the WSe2/CoSe2/CNFs anode shows excellent electrochemical performance, including high capacity (403.5 mAh g−1 at 0.2 A g−1), long-term cycling stability (333.5 mAh g−1 after 1800 cycles at 5 A g−1 with negligible capacity decay per cycle of only 0.0012 %) and remarkable rate performance (a reversible capacity of 312.6 mAh g−1 is achieved even at a high current density of 20 A g−1). Meanwhile, the excellent sodium storage performance of the WSe2/CoSe2/CNFs composites electrode was deeply investigated by kinetic analysis.