Design of V2O5•xH2O cathode for highly enhancing sodium storage

The V2O5 center dot xH(2)O films with various contents of tetravalent vanadium were controllably designed via a convenient electrodeposition followed by sintering. X-ray photoelectron spectroscopy (XPS) results showed that sintering at Ar can introduce more V4+ in V2O5 center dot xH(2)O films. As cathode electrodes for sodium ion batteries, the V2O5 center dot xH(2)O film with more V4+/defect exhibited a higher initial discharge capacity of 198 mAh g(-1) and higher capacity retention of 99% after 100 cycles at 200 mA g(-1), in comparison to the V2O5 center dot$xH(2)O film with lower V4+ (121 mAh g(-1) and 65%). Even at a high current density of 2000 mA g(-1), the superior reversible capacity of the films with more V4+ could reach 140 mAh g(-1). The results of electrochemical impedance spectroscopy and cyclic voltammetry revealed that more V4+/defects are beneficial to enhance sodium ions diffusion kinetics, resulting in better electrochemical reaction reversibility, ionic conductivity and sodium ions storage stability of the V2O5 center dot xH(2)O films sintered at Ar. As a result, this study provides a promising direction of V2O5 cathode in rechargeable sodium ion batteries. (C) 2017 Elsevier B.V. All rights reserved.