Heat-Resistant SPAN/TiO₂ Composite Nanofiber Separator for Safe and High-Performance Lithium-Ion Batteries

The performance of separators affects the safety and electrochemical properties of lithium-ion batteries (LIBs). Commercially available polyolefin separators face several limitations, such as inadequate thermal stability, flammability, and weak electrolyte wettability. In this research, a high-temperature-resistant and inorganic composite nanofiber separator based on thermal stabilization polyacrylonitrile (SPAN) was prepared. The hybrid separator was developed from a polyacrylonitrile (PAN) nanofiber membrane through impregnation and heat treatment processes, transforming PAN into a high-temperature-resistant SPAN. Additionally, a TiO2 coating was applied directly onto the nanofiber surfaces through an in situ deposition process. Compared with conventional polyolefin separators, the developed inorganic composite nanofiber separator exhibits improved thermal stability and electrolyte wettability. It maintains structural integrity at temperatures up to 300 °C, with water and electrolyte contact angles reduced to 0°. The composite separator features a porosity of 66.48% and an electrolyte uptake of 543.3%, resulting in an ionic conductivity of 2.35 mS/cm. The initial discharge specific capacity can reach 143.87 mAh·g–1 at 1 C, maintaining a capacity retention of 97.80% after 100 cycles for the LiFePO4 batteries with the composite separators. We believe that the experimental results afford a promising method to develop high-thermal-stability separators for LIBs.