Homogeneous porous aramid nanofiber separator as highly safe separators for lithium-sulfur batteries

Commercial polyolefin separators hinder the commercialization of lithium-sulfur batteries due to safety issues from poor thermal stability and mechanical properties. This study develops novel porous aramid fiber separator (ANFs) to address these challenges. We used cetyltrimethylammonium bromide (CTAB) as a pore-forming agent in ANFs created via scraper coating and phase transformation to tackle densification. The addition of CTAB improves the separator's porosity, crucial for enhancing electrochemical performance and electron transport. The composite separator with 1 wt% CTAB (1-ANFs) achieves high porosity (75%), satisfactory tensile strength (58.4 MPa), excellent thermo-mechanical properties, and flame retardancy, effectively preventing lithium dendrite growth. Its porous structure significantly increases electrolyte uptake (190%), and the contact angle of the 1-ANFs electrolyte (9.9°) is much lower than that of the polypropylene separator (40.3°), improving electron transfer and reducing interfacial resistance. Consequently, the initial specific capacity of the battery with 1-ANFs at 0.2 C is 775.3 mAh g^-1, with an average Coulombic efficiency of 99.5%. Even at 2 C, the battery performs well. This composite separator offers innovative solutions for battery applications in extreme environments.