In this work, NaV 3 O 8 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 NaV 3 O 8 $xH 2 O nanowires is decreased from 169.6 mA h g À1 to 145.8 mA h g À1 when cycled at 10 mA g À1 , it shows good capacity retention of ca. 91.1% after 50 cycles, much higher than that (51.9%) of the untreated sample. Annealed NaV 3 O 8 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.
NaV6O15 nanoflakes with a 3-D tunneled structure were synthesized by a two-step approach and the NaV6O15//LiMn2O4 ARLB system with superior cycling performance (ca. 80% at 1 C after 400 cycles) was constructed. The origins of such superior electrochemical properties were explained well.
A novel strategy involving the self-transformation of superficial LiV3O8 in a reducing atmosphere (H2/Ar) was reported to fabricate core–shell structured LixV2O5/LiV3O8 nanoflakes. The cycling stability and rate performance were significantly improved.
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