Uniform β-Na_0.33V₂O₅ nanorod cathode providing superior rate capability for lithium ion batteries

A vanadium bronze nanomaterial, β-Na_0.33V₂O₅, was synthesized using a facile sol-gel method followed by annealing at high temperature. The morphology of the sample was observed using a scanning electron microscope (SEM) and a transmission electron microscope (TEM), and the crystal phase was determined by x-ray diffraction (XRD) spectroscopy. The as-prepared sample displays a morphology of nanorods, and has a pure phase with a high crystallinity. When used as the cathode material for rechargeable lithium batteries, the β-Na_0.33V₂O₅ nanorods fired at 400 °C exhibit better electrochemical properties at a 2.0 V cutoff voltage than those at a 1.5 V cutoff voltage. Over the voltage range of 2.0-4.0 V, they can deliver an initial capacity of 221 mAh g^-1 at a 0.5 C rate, and retain 212 mAh g^-1 after 200 cycles, accounting for a capacity fading of only 0.02% per cycle. At a 5 C rate, the discharge capacity still reaches 146 mAh g^-1, displaying an outstanding rate capability. Control of the electrochemical window is proved to be an effective strategy in boosting the cycling stability of the β-Na_0.33V₂O₅ cathode in this work in spite of a discounted capacity. Results suggest the as-prepared β-Na_0.33V₂O₅ nanorods are promising for use as high-performance cathode materials for rechargeable lithium batteries.