Annealed NaV3O8 nanowires with good cycling stability as a novel cathode for Na-ion batteries

In this work, NaV3O8 nanowires are proposed as a novel cathode for a Na-ion battery for the first time. The as-prepared nanowires are characterized well by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectra, thermogravimetry (TG), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Sodium insertion/extraction properties of as-prepared nanowires with or without thermal treatment are compared. It is found that thermal treatment could remove some crystal water in the host, resulting in a contracted crystal volume. In comparison with the untreated sample, although the reversible discharge capacity of annealed NaV3O8·xH2O nanowires is decreased from 169.6 mA h g−1 to 145.8 mA h g−1 when cycled at 10 mA g−1, it shows good capacity retention of ca. 91.1% after 50 cycles, much higher than that (51.9%) of the untreated sample. Annealed NaV3O8 nanowires exhibit much better cycling stability and charge–discharge plateaus during the Na-ion insertion/extraction processes, which should be attributed to the contracted crystal volume and the increased crystallinity.