Ionic potency regulation of coagulation bath induced by saline solution to control over the pore structure of PBI membrane for high-performance lithium metal batteries

In this study, we have explored the use of water as a non-solvent for tuning the microstructure of polybenzimidazole (PBI) membranes, which are potential separators for lithium metal batteries (LMBs). The traditional method for membrane synthesis called nonsolvent-induced phase separation (NIPS), usually relies on hazardous and costly organic non-solvents. By dissolving sodium chloride (NaCl) in water, we could adjust the water ionic potency and the exchange speed of the non-solvent with the DMAC solution to change the micropore structure of the PBI membrane. With increasing NaCl concentration, the micropores in the PBI membrane transitioned from finger-like to sponge-like morphology. Compared to commercial separators like the Celgard separator, the PBI membrane with sponge-like micropores exhibited better regulation of lithium deposition and improved Li⁺ transportation capability due to its good wettability with the electrolyte. Consequently, the PBI membrane-based Li/Li symmetric cell and Li/LiFePO₄ full cell demonstrated superior performance compared to the Celgard-based ones. This research proposes an eco-friendly and scalable synthetic approach for fabricating commercial separators for LMBs, addressing the issue of lithium dendrite growth and improving overall battery safety and performance.