In-situ reinforced polyimide nanofiber membranes for highly efficient and safe lithium-ion batteries

Highly robust nanofibrous separators can effectively promote the battery's electrochemical performance and security. Here, we present a synergistically reinforced polyimide (PI) nanofiber membrane by tuning the regularity of PI chains while employing an in-situ PI reinforcement. The regularity of nanofibers and ordered region of PI chains is improved after hot stretching, thus enhancing the mechanical strength of PI nanofibers membrane. After synergistic PI-armor reinforcement, the reinforced PI nanofiber membrane with excellent thermotolerance and flame resistance exhibits a remarkable mechanical strength of 120.9 MPa, making them among the most robust PI nanofiber separators reported to date. Density functional theory calculations verify that the electron-rich sites of imide group in PI main chain can facilitate the desolvation of lithium-ion (Li+) and adsorb Li+ near imide groups of PI. Hence, the reinforced PI nanofiber separator with abundant 3D uniform nano-pore structure displays high ion conductivity (1.10 mS cm−1) and Li+ transfer number (0.58). Besides, Li symmetrical battery using the reinforced PI nanofiber membrane exhibits only a tiny voltage polarization during 300 h at 1.0 mA cm−2. These exceptional merits offer excellent specific capability (128.1 mA h g−1 at 5 C) to reinforced PI nanofiber membrane-based LIBs, along with 100-cycle battery stability at 1 C without significant capacity decay.