Polyetherimide membrane with tunable porous morphology for safe lithium metal-based batteries

The separator is critical in ensuring the safety and improving the electrochemical performance of lithium metal batteries (LMBs). However, the weak thermal stability, common mechanical strength and the poor wettability towards electrolyte of the commercial polyolefin separator severely hamper its application in high-performance LMBs. Herein, a simple phase inversion technique could be used to design and scalably fabricate porous polyetherimide (PEI) membranes, which was used as LMB separators for the first time. The final morphology of PEI membranes can be finely tuned from finger-like voids to sponge-like pores by selecting an appropriate non-solvent. Combining experiments and density functional theory (DFT) simulations, it reveals that the optimal PEI membrane shows a sponge-like pore structure, which can induce the genuine deposition of the Li metal due to the homogeneously distributed pores in high density on the membrane and its good affinity towards the electrolytes. Consequently, the PEI based LMB show better performance than the commercial polypropylene (PP) based LMB. More importantly, the optimal PEI membrane shows a better mechanical strength and thermal stability than the PP membrane at the same thickness, which can ensure a higher safety for real applications. Since the non-solvent induced phase separation technique used to prepare PEI membrane is scalable in low cost, this work provides insightful route to overcome one of the main challenges, i.e. lack of high performance and high safety separator, for practical LMB application.