Thermotolerant separator of cross-linked polyimide fibers with narrowed pore size for lithium-ion batteries

Separators are of significance in the thermal safety and energy-storage performance of lithium-ion batteries (LIBs). Thermotolerant separators of electrospun polyimide (PI) fibers hold great promise as candidate to commercial polyolefin-based separators due to their high thermal and electrochemical stability. However, their applications in LIBs are limited by the undesirably large pore size (∼2 μm) that will induce dendrite growth and thermal runaway of batteries. Here, we demonstrate a facile and scalable strategy to prepare thermotolerant separators of cross-linked PI fibers (c-PI) with a narrowed pore size (0.78 μm) via a blended electrospinning of polyamic acid and polystyrene followed by a thermal imidization. The electrospun fibers in the c-PI separator are ribborn-like and feature adhesion structure between adjacent fibers, while no such structures are observed for PI separator obtained without adding polystyrene. In comparison with the PI separators, the c-PI separator exhibits higher porosity, better electrolyte adsorption and higher ionic conductivity. In Comparison to the batteries with PI and Celgard separators, the battery with c-PI separator shows greatly enhanced electrochemical performance with a high capacity of 100.1 mAh/g at 10 C after 1600 cycles. This work offers a feasible and effective route to develop advanced membranes of electrospun fibers for safe LIBs.