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.