In Situ Electrochemically Oxidative Activation Inducing Ultrahigh Rate Capability of Vanadium Oxynitride/Carbon Cathode for Zinc-Ion Batteries

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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 (VN x O y /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 VN x O y /C cathode is greatly improved after the first charging process via in situ electrochemically oxidative activation. The oxidized VN x O y /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 Zn 2+ does not affect the crystal structure of oxidized VN x O y /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 H 2 O in the electrolyte are curial factors to activate VN x O y /C in that the oxygen replaces the partial nitrogen and creates abundant vacancies, inducing a conversion from VN x O y /C to VN x – m O y +2 m /C and then resulting in considerably strengthened rate performance and improved Zn 2+ storage capability. The study broadens the horizons of fast ion transport and is exceptionally desirable to expedite the application of high-rate ZIBs.