Separator engineering for high-energy rechargeable metal batteries: fundamentals, design strategies and perspectives

Rechargeable metal batteries hold outstanding prospects for next generation energy storage technologies due to their high theoretical capacities of metal anodes. However, the formidable problems regarding rampant dendrite growth, undesirable side reactions, and unstable solid electrolyte interfaces of metal anodes dramatically incurs short cycle lifetime and high safety risk. Separator engineering has triggered massive research activities as a simple yet effective strategy to mitigate these intractable issues in recent years. Herein, we offer a critical review on the significant advances of separator engineering for rechargeable metal batteries. To start with, the fundamentals of physiochemical and electrochemical requirements for separators are outlined. Subsequent discussion is specifically devoted to comprehend the design principles of various separator strategies, including pore adjustment, interfacial functionalization, and thermomechanical modulation, and to pave an in-depth understanding of their effectiveness on the performance improvement. Finally, the existing challenges and future perspectives of separator engineering are elaborately projected towards the development and practical deployment of safe and efficient rechargeable metal batteries.