A Long Cycle Life Zinc‐Iodide Flow Battery Enabled by a Multifunctional Low Cost Supporting Electrolyte

Abstract High energy density and cost‐effective zinc‐iodide flow battery (ZIFB) offers great promise for future grid‐scale energy storage. However, its practical performance is hindered by poor cyclability, because of irreversible zinc plating/stripping, slow kinetics of redox reactions, and solid I 2 precipitation. Herein, we report NaCl‐supported electrolyte chemistry to address these issues simultaneously. The formation of soluble chloride anions by coordination interactions between Zn 2+ and Cl − , are key factor for the improvement of Zn/Zn 2+ redox reversibility. While formation of soluble I 2 Cl − complex stabilizes ZIFB from I 2 precipitation, participation of Na + and K + as dominant migrating carriers passing through Nafion, restricts Zn 2+ migration, thus, blocking electrolyte crossover. A ZIFB with this improved electrolyte stably cycled 100 times with excellent capacity retention and energy efficiency at 20 mA cm −2 , while conventional ZIFB shows the trend of capacity fade from 10 th cycle onwards. These encouraging results of NaCl‐added electrolyte chemistry enlighten great prospects for high‐performance ZIFB applications.