Separator engineering for energy-dense and long-life rechargeable aqueous zinc metal batteries: A review

Rechargeable aqueous zinc metal batteries (RAZMBs) have emerged as a compelling alternative for grid-scale energy storage owing to their intrinsic safety, cost-effectiveness, and environmental benignity. However, the practical deployment of RAZMBs is currently hindered by the gap between theoretical potential and realized energy density, a discrepancy largely attributable to the reliance on thick, highly absorbent separators in laboratory settings. The separator is not merely a physical barrier but a pivotal component that governs ion transport kinetics, dendrite suppression, and, critically, the electrolyte-to-capacity (E/C) ratio of the cell. This review presents a comprehensive analysis of separator engineering for RAZMBs, moving beyond material synthesis to focus on the structural design principles required for high-energy-density and scalable devices. We systematically categorize recent advances in commercial, cellulose-based, synthetic polymer-based, and composite separators, evaluating them against engineering metrics such as thickness, wettability, mechanical strength, and roll-to-roll (R2R) processability. Particular emphasis is placed on modification strategies, including surface coatings and functional composites, that balance interfacial stability with industrial manufacturability. Finally, we provide a forward-looking perspective on overcoming the “lab-to-fab” bottlenecks, advocating for thin (< 20 μm), cost-effective (< 2 USD m− 2), and mechanically robust separators to unlock the full commercial potential of aqueous zinc batteries.