Progress and challenges of zinc-iodine flow batteries: From energy storage mechanism to key components

With the increasing need for intermittent natural energy resources, large-scale, long-term energy storage systems are increasingly required to make the best use of renewable power resources. Zinc-iodine redox flow batteries are considered to be one of the most promising next-generation large-scale energy storage systems because of their considerable energy density, intrinsic safety, environmental friendliness, and low unit energy storage cost. However, the development of zinc-iodine flow batteries still suffers from low iodide availability, iodide shuttling effect, and zinc dendrites. And unfortunately, a review regarding the battery as a whole incorporating the interplay between the positive and negative reactions to elucidate the impact of each key component on performance is still missing. This work summarized the strategies to address the above issues, including tailoring electrolyte compositions, modifying electrodes and membrane properties, and designing overall system devices. Moreover, the relevant mechanisms are illustrated, contributing to developing high-performance designs for zinc-iodine flow batteries with high energy density and a long lifespan.