In situ grown MOFs and PVDF-HFP co-modified aramid gel nanofiber separator for high-safety lithium-sulfur batteries

Safety-related issues have always been one of the most critical barriers hindering the large-scale popularization of high-energy-density storage systems. For lithium-sulfur (Li-S) batteries, conventional polyolefin separators with poor flash points and weak mechanical strength suffer from potential safety hazards that may cause fire and even explosion under extreme operating conditions. Herein, a thermotolerant poly-m-phenyleneisophthalamide (PMIA)-based gel polymer electrolyte separator (P-PMIA@ZIF-8) was designed by introducing high ion-conductive poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and in situ-grown zeolitic imidazolate framework-8 (ZIF-8) secondary nanostructures. The P-PMIA@ZIF-8 separator exhibited high-flux Li-ion diffusion and effective "shuttle effect" suppression due to its abundant multilevel pore structure and strong physicochemical anchoring ability toward soluble polysulfides (Li2Sx) resulting from the ZIF-8 secondary nanostructures. High mechanical properties (tensile strength and puncture force of up to 15 MPa and 0.95 N) and excellent thermal stability (no dimensional change even at an elevated temperature of 200 degrees C) of the P-PMIA@ZIF-8 separator can further physically block lithium dendrite growth and prevent the occurrence of potential safety accidents. Accordingly, the Li-S batteries with the P-PMIA@ZIF-8 separator delivered a reversible capacity of 855 mA h g(-1) after 300 cycles at 0.2C with a slow capacity decay of 0.086% per cycle. Even under the conditions of lean electrolyte (E/S = 5 mL g(-1)) and low N/P ratio (2.0), the P-PMIA@ZIF-8 separator still exhibited a steady cycling performance with a high gravimetric energy density of 216 W h kg(cell)(-1), highlighting its bright prospects in future high-energy-density battery systems.