Vanadium redox battery: Positive half-cell electrolyte studies

The vanadium redox battery (VRB) employs two “electrolyte tanks” that store energy in the form of the two vanadium redox couples and a cell “stack” where the charge/discharge reactions occur. To date, 2 M vanadium electrolyte have been successfully used in large demonstration projects for stationary applications. For mobile applications however, higher vanadium concentrations are required to reduce the size and weight of the battery. The main limitation for the vanadium electrolyte concentration and subsequently its energy density in the VRB is the thermal precipitation of the V(V) ion at elevated temperatures. In this paper optimization study of vanadium V(V) supersaturated solutions in terms of concentrations, temperature, and precipitation behavior are reported along with properties such as density and viscosity. It appears that 3.0–3.5 M V(V) solutions in 6 M total sulfate are sufficiently stable at temperatures up to 30 °C, although 2 M solutions are still required for operation at higher temperatures of about 40 °C.