Wide interlayer spacing ammonium vanadate (NH4)0.37V2O5.0.15(H2O) cathode for rechargeable aqueous zinc-ion batteries

Abstract

Recently, aqueous zinc-ion batteries (AZIBs) have been gaining widespread academic interest in the energy-storage field owing to their high energy density, enhanced safety of electrochemical operation, and low cost, as well as the abundance of zinc on earth. The ammonium vanadate group contains compounds that are considered efficient energy-storage materials because they provide two-dimensional (2D) layered structures with large interlayer distances that promote the intercalation of metal ions during electrochemical processes. Here, we report a hydrated form of ammonium vanadate (NH4)0.37V2O5·0.15(H2O) with a highly crystalline rose-like microstructure, which is used as the positive electrode material in AZIBs. The ammonium vanadate cathode delivered an initial capacity of 400mAh g−1 with 2M ZnSO4 at the current density of 0.5 Ag−1 in a voltage range from 0.2V to 1.4V vs Zn2+/Zn. At a higher current density (10 A g−1), the material retained 84% of the initial discharge capacity after 1000 cycles, while displaying an excellent rate capability. Cyclic voltammetry and ex-situ XRD and XPS are used to study the reaction mechanism of ammonium vanadate cathode in the AZIBs. Unlike other ammonium vanadate’s, (NH4)0.37V2O5·0.15(H2O) undergoes co-intercalation of Zn2+ and H+ along with water molecules. There is no intermediate irreversible crystal phase formation during the discharge/charge cycles due to expandable interlaying distance. This report suggests that (NH4)0.37V2O5·0.15(H2O) can be an alternative highly stable cathode material for use in AZIBs, and it can be promising for the intercalation of the cathode in larger-sized metal-ion storage systems.