Decoupled low-cost ammonium-based electrolyte design for highly stable zinc–iodine redox flow batteries

Abstract Zinc-iodine redox flow batteries (ZIFBs) have emerged as promising energy storage systems due to their high-energy density. However, their practical use has been limited by their poor stability, low efficiency and high cost. In this work, we implemented a novel strategy to improve the performance and cyclability of ZIFBs, as well as decrease the chemical cost, by developing and utilizing ammonium-based electrolytes. An ammonium chloride supported zinc-iodine redox flow battery (AC-ZIFB) based on the ammonium iodide/triiodide redox couple was designed, and it achieved a high energy density of 137 Wh L -1 , Coulombic efficiency of ~99%, energy efficiency of ~80%, and a cycle-life of 2500 cycles at a 11-times lower chemical cost than conventional ZIFBs. Such improvements are mainly attributed to the multifunctional roles of cost-effective chemicals utilized in a new decoupled electrolyte design, which mitigates zinc dendrite formation, facilitates anodic and cathodic reaction kinetics and unlocks extra capacity with the primary aid of I 2 C l − formation. This straightforward, yet effective strategy, empowers the AC-ZIFB with excellent potential as a robust and practical redox flow battery and more broadly demonstrates a facile strategy of using multifunctional electrolyte chemistry to achieve a reliable, high-performance, and cost-competitive energy storage system.