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 (V 2 O 5 ). In this study, the dissolution kinetics of V 2 O 5 in diluted sulfuric acid and commercial vanadium electrolyte (VE) is determined. The low solubility of V 2 O 5 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 V 2 O 5 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 VO 2 + 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.