Electrospun Polyimide Membrane for Mechanically and Thermally Durable High Performance Lithium‐Ion Battery Separator

Development of innovative processing methods capable of manufacturing large‐scale separators with high production efficiency while achieving thermal stability and mechanical robustness is essential for high‐performance lithium‐ion battery development. In this study, we proposed a scalable approach to produce nonwoven nanofiber web‐based polyimide (PI) separators, combining syringeless electrospinning with roll‐pressing treatment. This process yields large‐area poly(amic acid), followed by imidizaition, nanofiber membranes without pore damage, exhibiting excellent mechanical strength (∼22.2 MPa), and thermal stability up to 530 °C without structural deformation. The fabricated PI separator shows high ionic conductivity (3.5 mS cm ⁻¹ ) and lithium ion transference number of 0.68. Electrochemical evaluation shows that the NCM622//graphite full cell exhibits 168.9 mAh g ⁻¹ discharge capacity with 86.5% Coulombic efficiency at 0.1 C and retains 143.83 mAh g ⁻¹ after 200 cycles at 1 C, demonstrating superior long‐term cycling stability at high rate. Additionally, the PI‐based cell retains 91.02% of its capacity after 30 cycles at 45 °C under 0.5 C conditions. These results demonstrate that large‐scale, high‐efficiency processing enables practical production of high‐performance PI separators.