Budding willow branches shaped Na₃V₂(PO₄)₃/C nanofibers synthesized via an electrospinning technique and used as cathode material for sodium ion batteries

Budding willow branches shaped Na₃V₂(PO₄)₃/C nanofibers were successfully synthesized by a simple electrospinning technique with Poly(vinyl pyrrilidone) (PVP). The Na₃V₂(PO₄)₃/C nanoparticles that anchored on the nanofibers surface seemed like the willow buds; the inner core of the nanofibers, which composed Na₃V₂(PO₄)₃, looked like willow twig and the uniform carbon layer was same with willow bark. Such special morphology played a vital role in improving cycle stability and rate capability of the electrode due to the conductive network built up by nanofibers. The Na₃V₂(PO₄)₃/C nanofibers cathode exhibited an initial specific capacity of 106.8 mAh g^-1 at a current density of 0.2C, still stabling at 107.2 mAh g^-1 after 125 cycles with excellent cycle stability. Moreover, a capacity retention of 95.7% was obtained when Na₃V₂(PO₄)₃/C nanofibers cycled stepwise from 0.2 to 2C. Good electrochemical performance should be ascribed to both the special morphology and preferential growth of the (113) plane. The simple synthesis technique and good electrochemical performance suggests that this material with the special shape of budding willow branches is a promising cathode for sodium ion batteries.