Preparation of electrolyte for vanadium redox‐flow batteries based on vanadium pentoxide

The vanadium redox‐flow battery is a promising technology for stationary energy storage. A reduction in system costs is essential for competitiveness with other chemical energy storage systems. A large share of costs is currently attributed to the electrolyte, which can be significantly reduced by production based on vanadium pentoxide (V2O5). In this study, the dissolution kinetics of V2O5 in diluted sulfuric acid and commercial vanadium electrolyte (VE) is determined. The low solubility of V2O5 in sulfuric acid can be overcome by partially using VE with a state of charge of −50% as solvent. In this way, a complete dissolution of V2O5 is possible within ≈10 min to achieve the desired vanadium concentration of 1.6 mol L−1. Moreover, the electrochemical reduction of an electrolyte containing VO2+ coupled with the oxygen evolution reaction at the anode is investigated. For these consecutive steps, an electrical energy demand of 1.69 kWh kg−1 is required to reach a state of charge of −50%. Finally, both processes are integrated into a plant concept for continuous electrolyte production.