A Lewis Acid–Base Cooperative Separator Stabilizing Electrolytes in Lithium Metal Batteries

Manipulating electrolyte decomposition is an effective strategy to facilitate stable solid electrolyte interphase (SEI) formation and extend the lifetime of lithium metal batteries (LMBs). Here, a Lewis acid-base cooperative aramid nanofibers/poly(ethylene-co-acrylic acid) (ANFs/EAA) separator is designed to suppress the decomposition of the widely used LiPF₆-based electrolyte and promote the formation of LiF-rich SEI and cathode electrolyte interface. The Lewis acidic sites facilitate the dissociation of ion pairs and suppress the formation of PF₅ byproduct, while Lewis basic sites reduce the reactivity of inevitably generated PF₅ and prevent its further decomposition. This modularly designed separator with anchored Lewis acid and base regions synergistically promotes the formation of a robust interfacial layer without participating in interface reactions and introducing impurities. Impressively, even at the critical operating temperature of LiPF₆-based electrolyte of 60 °C, LiFePO₄||Li cells assembled with ANFs/EAA separators demonstrate exceptional cycling stability of over 200 cycles, ≈2.2 times longer than cells using PE separators. Furthermore, the high-temperature (50-70 °C) cycling performance of cells with ANFs/EAA separators significantly outperforms that of previously reported cells using LiPF₆-based electrolyte. This work provides a separator-engineering approach to stabilize electrolytes for robust cycling of LMBs with LiPF₆-based electrolytes at high temperatures.