Electrochemical performance and reaction mechanism investigation of V2O5 positive electrode material for aqueous rechargeable zinc batteries

Abstract

The electrochemical performance and reaction mechanism of orthorhombic V₂O₅ in 1 M ZnSO₄ aqueous electrolyte are investigated. V₂O₅ nanowires exhibit an initial discharge and charge capacity of 277 and 432 mA h g⁻¹, respectively, at a current density of 50 mA g⁻¹. The material undergoes quick capacity fading during cycling under both low (50 mA g⁻¹) and high (200 mA g⁻¹) currents. V₂O₅ can deliver a higher discharge capacity at 200 mA g⁻¹ than that at 50 mA g⁻¹ after 10 cycles, which could be attributed to a different type of activation process under both current densities and distinct degrees of side reactions (parasitic reactions). Cyclic voltammetry shows several successive redox peaks during Zn ion insertion and deinsertion. In operando synchrotron diffraction reveals that V₂O₅ undergoes a solid solution and two-phase reaction during the 1st cycle, accompanied by the formation/decomposition of byproducts Zn₃(OH)₂V₂O₇·2(H₂O) and ZnSO₄Zn₃(OH)₆·5H₂O. In the 2nd insertion process, V₂O₅ goes through the same two-phase reaction as that in the 1st cycle, with the formation of the byproduct ZnSO₄Zn₃(OH)₆·5H₂O. The reduction/oxidation of vanadium is confirmed by in operando X-ray absorption spectroscopy. Furthermore, Raman, TEM, and X-ray photoelectron spectroscopy (XPS) confirm the byproduct formation and the reversible Zn ion insertion/deinsertion in the V₂O₅.