Starch-mediated colloidal chemistry for highly reversible zinc-based polyiodide redox flow batteries

Aqueous Zn-I flow batteries utilizing low-cost porous membranes are promising candidates for high-power-density large-scale energy storage. However, capacity loss and low Coulombic efficiency resulting from polyiodide cross-over hinder the grid-level battery performance. Here, we develop colloidal chemistry for iodine-starch catholytes, endowing enlarged-sized active materials by strong chemisorption-induced colloidal aggregation. The size-sieving effect effectively suppresses polyiodide cross-over, enabling the utilization of porous membranes with high ionic conductivity. The developed flow battery achieves a high-power density of 42 mW cm −2 at 37.5 mA cm −2 with a Coulombic efficiency of over 98% and prolonged cycling for 200 cycles at 32.4 Ah L −1 posolyte (50% state of charge), even at 50 °C. Furthermore, the scaled-up flow battery module integrating with photovoltaic packs demonstrates practical renewable energy storage capabilities. Cost analysis reveals a 14.3 times reduction in the installed cost due to the applicability of cheap porous membranes, indicating its potential competitiveness for grid energy storage. The development of porous membranes that could work under high power density brings promise but a challenge with polyiodide cross-over for aqueous Zn-I flow batteries. Here, the authors develop a colloidal starch-based catholyte to inhibit cross-over that endows reversible flow cell performance.