A thermomechanically stable nanofiber separator with multiscale MOF networks towards high-efficiency ion transport†

Abstract

Pursuing high-energy-density and high-safety lithium-metal batteries (LMBs) is crucial for developing next-generation high-energy storage systems. However, uncontrollable lithium (Li) dendrite growth and the unstable solid electrolyte interface (SEI) make this task rather challenging. Here, a thermomechanically stable nanofiber separator composed of 3D multiscale metal–organic framework (MOF) networks was developed by an electrospinning-assisted in situ self-assembly strategy. This design ingenuity lied in building close-packed ZIF-8 nanounits onto polyimide (PI) nanofiber to construct 1D well-ordered MOF nanofibers and generate monolithic 3D networks, thereby providing continuous and fast Li⁺ linear transport pathways at the micrometer scale. Lewis acid sites and sub-nano pores within ZIF-8 served as ion sieves, selectively restricting larger anion movement to accelerate Li⁺ transport. Density functional theory calculations further verified the higher adsorption energy for Li-solvated clusters and the de-solvation effect on the ZIF-8 surface, facilitating high-efficiency and well-distributed Li⁺ intercalation. Moreover, these PI@ZIF-8 nanofiber separators contributed to constructing LiF-concentrated SEI films and reducing active Li and electrolyte consumption. Coupled with their excellent thermal stability, high mechanical strength and flexibility, potential safety accidents were effectively avoided. The resultant LMBs presented improved discharge capacity, cycling durability and stability, even under high-rate or high-temperature conditions, charting a promising course for developing high-quality nanofiber separators for advanced LMBs.