Ionic Covalent Organic Framework Membrane as Active Separator for Highly Reversible Zinc–Sulfur Battery

Zinc-sulfur (Zn-S) batteries exhibit a high theoretical energy density, nontoxicity, and cost-effectiveness, demonstrating significant potential for integration into large-scale energy storage systems. However, the phenomenon of polysulfide (including dissolved S8 and S x 2–) shuttling is a major issue that results in rapid capacity decay and a short lifespan, limiting the practical performance of sulfur-based batteries. Herein, we fabricated an ionic covalent organic framework (iCOF) membrane as an active separator for the Zn-S battery. Sulfonic acid groups were introduced to the COF membrane, providing abundant negative charge sites in its pore wall. By combining size sieving and charge interaction between the polysulfide and pore wall, the iCOF membrane inhibited the crossover of polysulfides to the Zn metal anode without affecting the transport of metal ions. The Zn-S battery with the iCOF membrane as the separator shows a high-performance and low attenuation rate of 0.05% per cycle over 300 cycles at 2.5 A g–1. This study emphasizes the significance of separator design in enhancing Zn-S batteries and showcases the potential of functionalized framework materials for the development of high-performance energy storage systems.