Solvothermal synthesis of VO2 and in situ electrochemical transformation of Zn2V2O7 as cathode for long-life aqueous zinc-ion batteries

Abstract

VO2 is a good cathode material for aqueous zinc ion batteries (AZIBs). However, V4+ is not stable in weakly acidic aqueous electrolyte, while the voltage range of AZIBs with VO2 as cathode in charge/discharge test is limited, usually below 1.5 V. In this paper, VO2 is synthesized by solvothermal method and in situ electrochemically converted to Zn2V2O7 as cathode material for AZIBs with superior performance, and the two drawbacks of narrow voltage range in charge/discharge test and easy dissolution of V4+ are solved. After 10 cycles, the VO2 cathode offers a discharge specific capacity of 408.4 mAh g−1 from an initial discharge specific capacity of 329.8 mAh g−1 at a current density of 0.1 A g−1. After 124 cycles, the maximum discharge capacity is 271.7 mAh g−1, while the initial discharge capacity is 16.2 mA h g−1 at a current density of 10 A g−1. The results of XRD and XPS show that the VO2 cathode is in situ electrochemically transformed into Zn2V2O7 within the first few cycles. With its improved performance, high cycle stability under long cycles and high current density, the in-situ converted Zn2V2O7 offers a new approach for the development of cathode materials for AZIBs.