Advancements in separator materials for aqueous zinc batteries

Aqueous zinc (Zn) batteries (AZBs) are becoming promising candidates for grid-scale energy storage because of their inherent safety, cost-effectiveness, and high theoretical capacity. However, their widespread application is hindered by critical challenges, including Zn dendrite formation, hydrogen evolution reaction (HER), corrosion, and cathode material dissolution. The separator plays a crucial role in regulating ion transport, suppressing side reactions, and promoting uniform Zn deposition. While recent advancements in separator design have introduced various modification strategies to enhance electrochemical performance, a systematic classification based on the modification location remains lacking. This review provides a comprehensive analysis of recent advancements in AZB separators, categorized by modification position-anode side, cathode side, and full-separator modifications. Key modification strategies, including ion-selective layers, interfacial engineering, and composite functional membranes, are discussed in detail, with an emphasis on their effects on Zn²⁺ flux regulation, dendrite suppression, and long-term cycling stability. Additionally, emerging separator materials such as covalent organic frameworks (COFs), metal-organic frameworks (MOFs), and inorganic-organic hybrid separators are highlighted for their potential in optimizing battery performance. By elucidating the underlying mechanisms governing separator modifications, this review provides theoretical insights and design principles for the development of next-generation AZB separators. Finally, we discuss future research directions, focusing on separator thinness, enhanced ion selectivity, interface stability, corrosion resistance, and scalable manufacturing to accelerate the commercialization of high-performance AZBs.