Bottlenecks and Techno-Economic Feasibility of the Zinc–Iodine Flow Battery

Zinc–iodine flow batteries (ZIFB) have emerged as one of the most promising technologies for next-generation grid-scale energy storage systems due to their advantages, which include high energy density, low cost, and environmental friendliness. However, the practical applicability of ZIFB is mainly hindered by low electrolyte utilization, the zinc dendrite problem, iodine precipitation, and membrane instability. Since the negative electrode involves plating of zinc, it is essential to achieve high areal capacity, volumetric capacity, and effective electrolyte utilization, all together. Most literature reports either high volumetric or geometric capacity, but not combined. Those who report high capacities fail to report the same in long-term cycling. Some work explores asymmetric electrolytes whose performance is affected by the crossover of the electrolytes. Although many reviews on the static version of the zinc–iodine battery exist, reviews of ZIFB are scant. This review primarily focuses on the present status and challenges of ZIFB. It offers a comparative analysis of ZIFB with other redox flow batteries and the key factors related to zinc dendrite issues, water shifting, iodine precipitation, and the interaction of iodine species with commonly used polymer membranes. Additionally, the review explores the strategies employed to overcome these challenges, including the use of electrolyte additives (both organic and inorganic), electrode modifications, and cost-effective alternatives to the Nafion membrane. The review concludes by outlining the remaining challenges of ZIFB and the future pathway to address these issues.