An in-situ electrochemical oxidation strategy of VPO4 and its performance as a cathode in aqueous Zn-ion batteries

摘要

Benefiting from the security and low cost, aqueous rechargeable Zn-ion batteries (ZIBs) have currently become attractive candidate devices for energy storage. However, the scarcity of appropriate materials served as cath-odes is one of the major issues that hinder the development of aqueous ZIBs. VPO4 is considered as a promising cathode material for energy storage with huge potential windows and high specific capacity due to the stable structure caused by the stable PO4 polyanionic group and the various oxidation states of V element. However, due to the low valence state of V, as Zn2+ host structure, PO4 could not be effectively discharged directly. Herein, by an in situ electrochemical anodic oxidation method, we successfully improved the valence state of V and a higher valence vanadium-based compound (Zn0.11VO(PO4)center dot 2.5H2O) was obtained. As expected, due to the increased valence state of V element and obviously reduced particle size caused the in situ electro-chemical oxidation, the assembled Zn/VPO4 cells exhibits high reversible specific capacity of about 210 mA h g-1 at 50 mA g-1 and a good rates cycling stability. Furthermore, the efficient in situ electrochem-ical oxidation process of VPO4 cathode and the reversible Zn2+ ions insertion/extraction mechanism in the sub-sequent cycles have been investigated through in situ XRD diffraction, field emission scanning electron microscopy (FESEM) and ex situ XRD photoelectron spectroscopy (XPS). This work also provides a novel method to design the high performance Zn ion cathode material.

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