Highly porous and thermally stable zeolitic imidazolate framework-8/aramid nanofibers composite separator for lithium-ion batteries

Currently, the inferior electrolyte wettability and poor thermal stability of conventional polyolefin separators have impeded the development of high-performance lithium-ion batteries (LIBs). Herein, a novel zeolitic imidazolate framework-8 (ZIF-8)/aramid nanofibers (ANFs) composite separator was fabricated via in-situ assembling ZIF-8 on ANFs followed by filtration process. The ZIF-8 particles prevented the dense packing of ANFs and significantly improved the porosity from 23.8% (in pure ANFs separator) to 61.6% (in composite separator). Combining the well-developed porous structure and exceptional electrolyte affinity, the as-prepared 30%ZIF-8/ANFs composite separator (with 30 wt% of ZIF-8) exhibited high electrolyte uptake (224.0%) and good electrolyte wettability, which brought about superior ionic conductivity (1.37 mS cm−1), excellent rate performance and cycling stability. Furthermore, compared to commercial polypropylene separator, the 30%ZIF-8/ANFs separator showed suitable mechanical strength, outstanding thermal resistance and flame retardancy, which ensured higher safety during battery operation. Accordingly, the 30%ZIF-8/ANFs composite separator with both enhanced performance and high safety is a promising candidate for next-generation LIBs.