As a promising candidate for large-scale energy storage, aqueous zinc-ion batteries (ZIBs) still lack cathode materials with large capacity and high rate capability. Herein, a spherical carbon-confined nanovanadium oxynitride with a polycrystalline feature (VNxOy/C) was synthesized by the solvothermal reaction and following nitridation treatment. As a cathode material for ZIBs, it is interesting that the electrochemical performance of the VNxOy/C cathode is greatly improved after the first charging process viain situ electrochemically oxidative activation. The oxidized VNxOy/C delivers a greatly enhanced reversible capacity of 556 mAh g-1 at 0.2 A g-1 compared to the first discharge capacity of 130 mAh g-1 and a high capacity of 168 mAh g-1 even at 80 A g-1. The ex situ characterizations verify that the insertion/extraction of Zn2+ does not affect the crystal structure of oxidized VNxOy/C to promise a stable cycle life (retain 420 mAh g-1 after 1000 cycles at 10 A g-1). The experimental analysis further elucidates that charging voltage and H2O in the electrolyte are curial factors to activate VNxOy/C in that the oxygen replaces the partial nitrogen and creates abundant vacancies, inducing a conversion from VNxOy/C to VNx-mOy+2m/C and then resulting in considerably strengthened rate performance and improved Zn2+ storage capability. The study broadens the horizons of fast ion transport and is exceptionally desirable to expedite the application of high-rate ZIBs.
Keywords: VNxOy/C; cathode materials; in situ electrochemical oxidation; ultrahigh rate capability; zinc-ion batteries.