Enhanced reversibility of vanadium oxide cathode by diminished surface precipitation in Zn(TFSI)2 aqueous electrolyte

Abstract

Rechargeable aqueous zinc-ion batteries (RAZIBs) are considered promising energy storage system for large-scale applications due to their advantages of low cost, inherent safety, and environmental friendliness. Developing advanced cathode materials with stable cycle performance is the major focus in this field. However, relationships between electrolyte components and battery performance are not fully understood. In the present work, Zn(TFSI)2 aqueous electrolyte is demonstrated to provide enhanced electrochemical performance of Zn0.17V2O5•0.95H2O (ZVO) cathode, that is, high capacity (390 mAh g−1 at 1 A g−1) and stable cycle performance (77.7% after 6,000 cycles at 6 A g−1) can be achieved. By contrast, ZVO in ZnSO4 electrolyte exhibits comparable discharge capacity initially (355 mAh g−1 at 1 A g−1), but the cycle performance is much deteriorated (20.4% after 6,000 cycles at 6 A g−1). As examined by X-ray Diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and electrochemical impedance spectroscopy (EIS), the results indicate that using Zn(TFSI)2 aqueous electrolyte reduces surface precipitation allowing boosted ions diffusion kinetics in ZVO host material upon charging, resulting in highly reversible energy storage. Moreover, another crystal structure (one-dimensional tunneled V2O5) also demonstrates the superior performance enabled by Zn(TFSI)2 electrolyte.