Ultra long single crystalline Na0.3V2O5 nanofibers/nanorings synthesized by a facile one pot green approach and their lithium storage behavior

In this work, a simple one step hydrothermal method to synthesize Na0.3V2O5 nanofibers/nanorings without using any surfactant at 200 ºC in 3-5 days is reported. The products were characterized by X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), UV-Vis spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electrochemical discharge-charge test for lithium ion batteries. XRD patterns showed that, at 200 ºC for 2 and 3-4 days, Na0.3V2O5•1.5H2O belts and Na0.3V2O5 nanofibers/rings were formed, respectively. The FTIR spectrum revealed peaks at 1003 and 956 cm-1 assigned respectively to V5+=O and V4+=O. The UV-Vis spectrum showed maximum absorbance at 404 nm (3.07 eV). TEM analyses revealed a large quantity of fibers 70-100 nm thick and 20-90 mm long, and rings with diameters of ca. 20 µm and thickness of 70-150 nm. The nanofibers/rings exhibited an initial discharge specific capacity of 182 mAh g-1 and a stabilized capacity of 179 mAh g-1 even after 50 cycles. A possible mechanism for ring formation is discussed.