High-strength, thermally stable nylon 6,6 composite nanofiber separators for lithium-ion batteries

Electrospun nylon 6,6 composite nanofiber membranes containing TiO₂ or SiO₂ nanoparticles were fabricated, and their physical and electrochemical properties were assessed for use as high-strength, thermally stable separators for lithium-ion batteries. Experimental results demonstrated that TiO₂/nylon 6,6 and SiO₂/nylon 6,6 nanofiber membranes not only displayed good mechanical strength and excellent thermal stability, but also showed improved electrochemical properties compared to commercial polypropylene membrane separator. Larger liquid electrolyte uptake, higher ionic conductivity, higher electrochemical oxidation limit, and lower interfacial resistance with lithium were obtained for TiO₂/nylon 6,6 and SiO₂/nylon 6,6 nanofiber membranes. Among all membranes studied, SiO₂/nylon 6,6 nanofiber membranes showed the highest ionic conductivity and lowest interfacial resistance with lithium owing to their highest porosity and well-dispersed nanoparticles. In addition, Li/LiCoO₂ and Li/LiFePO₄ cells containing these composite nanofiber membranes demonstrated high cell capacities, good cycling performance, and superior C-rate performance at room temperature.