Economical preparation of vanadium electrolytes via ascorbic acid-driven reduction of vanadium pentoxide

With the growing demand for stable energy storage technologies driven by the expansion of renewable energy sources, vanadium flow batteries (VFBs), which are known for their high stability and long cycle life, have garnered significant attention. Nevertheless, the high production cost of vanadium electrolytes remains a major obstacle to the widespread commercialization of VFBs, highlighting the urgent need for the development of low-cost production methods. This study details a synthetic process for vanadium electrolytes using ascorbic acid (AA) to reduce vanadium pentoxide (V₂O₅). The reduction reaction rate is spectroscopically evaluated depending on temperature and AA concentration, and the concentration of sulfuric acid is optimized based on analysis of the reduction process and ion consumption. Step tests and VFB full cell evaluations are then conducted using electrolytes prepared with different AA concentrations. As a result, VFBs including electrolyte containing 105 % of the stoichiometric concentration of AA exhibit comparable efficiency and capacity to those including conventional VOSO₄-based electrolyte. In contrast, excessive or insufficient concentration of AA induces self-discharge and initial capacity loss. Based on that, this study proposes how a low-cost V₂O₅-based vanadium electrolyte is prepared with reducing agent, suggesting guidelines for fabrication of the V₂O₅-based vanadium electrolyte.