A high-safety and multifunctional MOFs modified aramid nanofiber separator for lithium-sulfur batteries

High-level safety is the essential precondition for the future large-scale applications of the high-energy storage systems. In terms of the lithium-sulfur (Li-S) batteries, the low flash point and poor mechanical strength of the conventional polyolefin separator are the potential safety hazards to cause the fire and explosion in extreme environment. Herein, a thermotolerant and nonflammable hierarchical functional separator (Z-PMIA separator) is designed based on the poly(m-phenylene isophthalamide) (PMIA) membrane and the in-situ formed Co-containing zeolitic imidazolate framework ZIF-L(Co) secondary nanostructures. Benefiting from the feature of “Aramid” fibers and the special secondary ZIF-L(Co) nanostructures, the Z-PMIA separator not only guarantees high mechanical strength (suffering from a tensile strength of 15 MPa and a puncture force of 0.95 N) and remarkable thermal stability (no dimensional shrinkage even at 200 °C) but also effectively suppresses the polysulfide shuttle and lithium dendrite growth. As a result, the Z-PMIA separator delivers a high initial discharge capacity of 1391.2 mAh g⁻¹ and a discharge capacity of 961.1 mAh g⁻¹ after 350 cycles at 0.2C, with a slow capacity attenuation of 0.033% per cycle. Even under the conditions of high sulfur loading (9.23 mg cm⁻²) and low electrolyte/sulfur (E/S) ratio (8 mL g⁻¹) or when running at a high temperature (80 °C), the Z-PMIA separator still enables a high charging/discharging performance, highlighting its promising commercial prospect for future high-safety and high-performance energy storage systems.