Ionic\nCovalent Organic\nFramework Membrane as Active\nSeparator for Highly Reversible Zinc–Sulfur Battery

Zinc-sulfur\n(Zn-S) batteries exhibit a high theoretical\nenergy\ndensity, nontoxicity, and cost-effectiveness, demonstrating significant\npotential for integration into large-scale energy storage systems.\nHowever, the phenomenon of polysulfide (including dissolved S<sub>8</sub> and S<sub><i>x</i></sub><sup>2–</sup>) shuttling\nis a major issue that results in rapid capacity decay and a short\nlifespan, limiting the practical performance of sulfur-based batteries.\nHerein, we fabricated an ionic covalent organic framework (iCOF) membrane\nas an active separator for the Zn-S battery. Sulfonic acid groups\nwere introduced to the COF membrane, providing abundant negative charge\nsites in its pore wall. By combining size sieving and charge interaction\nbetween the polysulfide and pore wall, the iCOF membrane inhibited\nthe crossover of polysulfides to the Zn metal anode without affecting\nthe transport of metal ions. The Zn-S battery with the iCOF membrane\nas the separator shows a high-performance and low attenuation rate\nof 0.05% per cycle over 300 cycles at 2.5 A g<sup>–1</sup>.\nThis study emphasizes the significance of separator design in enhancing\nZn-S batteries and showcases the potential of functionalized framework\nmaterials for the development of high-performance energy storage systems.