Enhanced Solubility and Stability of Polysulfide/Ferrocyanide Redox Flow Batteries

Redox flow batteries are a promising solution for large-scale stationary renewable energy storage, capable of consistently delivering power to the grid. However, achieving high energy density, long-term stability, and low cost remains a challenge. Vanadium redox flow batteries as a present candidate are limited by their high cost and low energy density, which causes the search for alternative options for redox systems. Sulfide-based systems can raise interest for anolytes due to their abundance, high capacity, and low cost. Despite this high potential, the polysulfide species present in the anolyte solution are suffered from sluggish redox reactions and irreversible crossover through the cation exchange membrane, resulting in significant capacity fading and reduced cycle life.<br/><br/>In this study, we revisit the polysulfide redox couple and demonstrate enhanced cycling performance including boosted energy density and cycle life. A promising electrolyte engineering strategy has been evaluated to increase the solubility of polysulfide species, and new permselective membranes with an improved polysulfide blocking ability were used to slow down the crossover of polysulfides. The mechanisms underlying the enhancement were investigated using multimodal methods to elucidate the structures of electrolyte solutions and membrane materials.