Na Insertion Mechanisms in Vanadium Oxide Nanotubes for Na-Ion Batteries

In this study, we successfully synthesized lamellar-structured Ni0.1VOx NTs by a microwave-assisted hydrothermal method and cation exchange reaction. High initial discharge capacity and 100% efficiency were obtained when the Ni0.1VOx NTs cathode was used as a cathode material for the Na battery. The intercalation mechanism and capacity fading effect were investigated in detail both experimentally using Transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) analyses and theoretically using the ab initio simulation method. During the intercalation of Na+ into VOx NT structures, TEM, XRD, FT-IR, and XPS data revealed the cointercalation of the solvent, resulting in the expansion of the interlayer spacing and carbon and oxygen adsorption. The experimental and simulation results suggest that solvent molecules coordinated the Na insertion mechanisms into the amine interlayer during discharging. These understandings of the Na intercalation mechanism in materials based on Ni0.1VOx NTs would be useful to design more stable and high-performance VOx-based electrodes for Na battery applications.