Recent Progress on Electrolytes and Separators of Aqueous Zinc–Iodine Batteries: Mechanisms, Challenges and Perspectives

Aqueous zinc-iodine batteries (AZIBs) have emerged as highly promising energy storage systems because of their inherent safety and low cost. However, conventional two-electron AZIBs (2eZIBs) are limited by their relatively low energy density (211 mAh g −1 based on the I − /I 2 2e reaction), while four-electron AZIBs (4eZIBs) can potentially double the capacity to 422 mAh g −1 but still face critical challenges, including polyiodide shuttling, I + hydrolysis, and zinc dendrite growth. Here, we systematically analyze the energy storage mechanisms of AZIBs, focusing on the differences and stability issues between two-electron (I − /I 2 ) and four-electron (I − /I 2 /I + ) redox pathways. To address these challenges, this review comprehensively summarizes electrolyte optimization strategies (e.g., functional additives and gel electrolytes) and separator modification approaches for suppressing polyiodide shuttles, stabilizing I + oxidation states, and optimizing zinc deposition behavior. Additionally, we evaluate the practical energy density of AZIBs and suggest future research directions, including the design of functionalized asymmetric electrolytes and the implementation of interface engineering approaches to optimize separators, thereby facilitating the practical application of AZIBs in large-scale energy storage systems. This review systematically elaborates the energy storage mechanisms and key challenges facing both the cathode and anode in AZIBs, while also providing an in-depth discussion of regulatory strategies such as electrolyte optimization and separator modification. Collectively, these insights offer theoretical guidance for the development of high energy density and long cycle life AZIB systems.