Yolk-Shell Structured ST@Al 2 O 3 Enables Functional PE Separator with Enhanced Lewis Acid Sites for High-Performance Lithium Metal Batteries.

Commercial polymer separators usually have limited porosity, poor electrolyte wettability, and poor thermal and mechanical stability, which can deteriorate the performance of battery, especially at high current densities. In this work, a functional polyethylene (PE) separator is prepared by surface engineering a layer of Ti-doped SiO 2 @Al 2 O 3 particles (denoted as ST@Al 2 O 3 -PE) with strong Lewis acid property and uniform porous structure on one side of the PE separator. On the other hand, ST@Al 2 O 3 particles with abundant pore structures and large cavities can store a large amount of electrolyte, providing a shortened pathway for lithium-ion transport, and the Lewis acid sites and porous structure of the ST@Al 2 O 3 can tune Li plating/stripping behavior and stabilize the lithium metal anode. The ST@Al 2 O 3 -PE separators exhibit better ionic conductivity (5.55 mS cm -1 ) and larger lithium-ion transference number (0.62). At a current density of 1 mA cm -2 , Li/Li symmetric cells with ST@Al 2 O 3 -PE separator can be stably cycled for more than 400 h, and both lithium iron phosphate /Li cells and lithium cobaltate/Li cells with ST@Al 2 O 3 -PE separator have good cycling and rate performance. This work provides a new strategy for developing functional separators and promoting the application of lithium metal batteries.