Na Insertion\nMechanisms in Vanadium Oxide Nanotubes\nfor Na-Ion Batteries

Abstract

In\nthis study, we successfully synthesized lamellar-structured\nNi_0.1VO_<i>x</i> NTs by a microwave-assisted\nhydrothermal method and cation exchange reaction. High initial discharge\ncapacity and 100% efficiency were obtained when the Ni_0.1VO_<i>x</i> NTs cathode was used as a cathode\nmaterial for the Na battery. The intercalation mechanism and capacity\nfading effect were investigated in detail both experimentally using\nTransmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier\ntransform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy\n(XPS) analyses and theoretically using the ab initio simulation method.\nDuring the intercalation of Na⁺ into VO_<i>x</i> NT structures, TEM, XRD, FT-IR, and XPS data revealed the\ncointercalation of the solvent, resulting in the expansion of the\ninterlayer spacing and carbon and oxygen adsorption. The experimental\nand simulation results suggest that solvent molecules coordinated\nthe Na insertion mechanisms into the amine interlayer during discharging.\nThese understandings of the Na intercalation mechanism in materials\nbased on Ni_0.1VO_<i>x</i> NTs would\nbe useful to design more stable and high-performance VO_<i>x</i>-based electrodes for Na battery applications.