Morphological modulation of the PBI membrane and performance optimization for Li-metal battery

A series of Polybenzimidazole (PBI) membranes with tunable porous structure were prepared using the classical non-solvent induced phase separation method by adjusting the proportions of non-solvent H₂O/EtOH. With the increase of ethanol concentration, the PBI membrane gradually change from the asymmetric finger-like structure to the highly interconnected spongy porous architecture (PBI-E70 and PBI-E100). Moreover, the as-prepared PBI membranes, especially for the PBI-E70 sample, display better electrolyte affinity, ionic conductivity, thermal stability, and mechanical strength than the PP separator. As expected, the Li//Li symmetric cell using PBI-E70 exhibits longer life span (500 h) with lower polarization values (13 mV) than other PBI or PP cells; the PBI-E70 based Li//LiFePO₄ cell shows superior cyclic stability (0.5 C) and rate capability than the other cells. The highly improved cell performance of the PBI-E70 is not only attributed to its chemistry multifunctionality, but also its interconnected sponge network to facilitate ordered ion transportation and guide uniform lithium deposition/dissolution, which has been verified by the COMSOL simulation. This study provides a simple and cost-effective method to prepare membrane with tunable morphology as well as its superb performance for Li metal battery.