A microfluid-on-microfluid phase separation strategy fabricates high-throughout porous polyimide separator for lithium-ion batteries

The microstructures and thermal stability of separators are critical for the safety and performance of lithium-ion batteries; however, it is still challenging to fabricate advanced separators simultaneously achieving uniform and high-throughput interconnected microporous structures with high thermal stability. Here, based on a soluble polyimide (PI) with high thermal stability, we report a microfluid-on-microfluid phase separation strategy (MF²-PS) to address the above challenge. Compared to the traditional non-solvent induced phase separation by immersion, the MF²-PS strategy can achieve more controlled porous structures with sponge-like open channels at submicron scale. The high surface polarity of the PI-separator also exhibited good wettability with liquid electrolytes, and a high electrolyte uptake (182 wt%) for achieving a high ion-conductivity. It also showed much superior thermal stability as compared to PP separator. Finally, due to the unique porous structures, the PI-separator by MF²-PS strategy successfully delivered a discharge capacity of 161.9 mA h g⁻¹ for LiFePO₄ electrode, and very stable cycling performance. All these results indicates that the PI-separator by MF²-PS may find significant applications in safe and high-performance batteries. © 2024 Elsevier Ltd.