Sandwich-Structured FPI-PEO@ZIF-8/Celgard/FPI-PEO@ZIF-8 Separator for High-Performance Room-Temperature Sodium-Sulfur Batteries

Room-temperature sodium-sulfur (RT Na-S) batteries offer a compelling avenue for grid-scale energy storage owing to the abundance of sodium resources and high theoretical energy density, but their commercialization is hindered by polysulfide shuttles and sodium dendrites piercing. In order to solve these problems, a sandwich structure FPI-PEO@ZIF-8/Celgard/FPI-PEO@ZIF-8 separator was designed and fabricated, with commercial Celgard as the intermediate support layer and FPI-PEO@ZIF-8 fiber membrane as the symmetrical functional layer. Leveraging the mechanical strength of Celgard and the pliable three-dimensional network of FPI-PEO@ZIF-8 fiber membranes, the hybrid separator mitigates the growth of sodium dendrites and blocks their subsequent piercing. Meanwhile, composite separator suppresses the shuttle of polysulfide through the synergistic effect of “electrostatic repulsion-chemical trapping” due to the presence of fluorine-containing groups and ZIF-8. When evaluated at a high current density of 3 A g-1, the RT Na-S battery employing the sandwich-structured separator retains a reversible capacity of 642 mAh g-1 over 1000 cycles. Symmetric Na||Na battery employing this sandwich-structured separator has a stable cycle of more than 1800 hours, which is significantly longer than Celgard’s 380 hours. This work demonstrates a scalable strategy for fabricating advanced separators and promotes the practical application of RT Na-S batteries in large-scale energy storage.