Critical-Point-Dried, Porous, and Safer Aramid Nanofiber Separator for High-Performance Durable Lithium-Ion Batteries.

Ionically conducting, porous separator membranes with submicrometer size pores play an important role in governing the outcome of lithium-ion batteries (LIBs) in terms of life, safety, and effective transport of ions. Though the polyolefin membranes have dominated the commercial segment for the past few decades, to develop next-generation batteries with high-energy density, high capacity, and enhanced safety, there is a need to develop advanced separators with superior thermal stability, electrolyte interfacial capabilities, high melting temperature, and mechanical stability at elevated temperatures. Here, aramid nanofiber separators with enhanced mechanical and thermal stability dried at the critical point are processed and tested for mechanical strength, wettability, electrochemical performance, and thermal safety aspects in LIBs. These separators outperform Celgard polypropylene in all aspects such as delivering a high Young's modulus of 6.9 ± 1.1 GPa, and ultimate tensile strength of 170 ± 25 MPa. At 40 and 25 °C, stable 200 and 300 cycles with 10% and 11% capacity fade were obtained at 1 C rate, respectively. Multimode calorimetry, specially designed to study thermal safety aspects of LIB coin cells, demonstrates low exothermicity for critical-point-dried aramid nanofiber separators, and post-diagnosis illustrates preservation of structural integrity up to 300 °C, depicting possibilities of developing advanced safer, high-performance LIBs.