Selectively Permeable Mesoporous Separator Coating by Anti-Gravity 2D-Microfluidic for Lithium Metal Batteries

Abstract

Selective permeable membranes for ions are of great interest for the development of next-generation batteries. Here, by harnessing the strong capillary effect of commercial battery separators with nanoscale porous structures, we report a super-efficient and industry-friendly anti-gravity two-dimensional microfluidic (2D-MF) nanophase separation strategy to fabricating ultrathin separator coating with selective permeation to lithium ion. This 2D-MF can effectively inhibit the Rayleigh-Taylor instability of 2d-microfluid and form well-controlled fluid coating with thickness ranging from nanoscale to microscale as evidenced by both simulation and experiment results. Moreover, the unique evaporation-induced heterogenous lean-crystallization behaviors of the 2D-MF composed of piezoelectric poly(vinylidene difluoride) (PVDF) and lithium salt are found as the key to realize the desired mesoporous functional coating. The resultant selectively permeable mesoporous coated polyethylene separator (SPMC@PE) is a promising solution to lithium-metal batteries as it can improve the lithium-ion permeation selectivity by 72% compared to the benchmark and generate LiF-rich component to stabilize the solid-electrolyte-interphase (SEI) layer. As a result, the lithium metal anode can be stably cycled for 500 cycles even at harsh testing condition (1 mA cm^-2 and 1 mAh cm^-2).