Yolk-Shell Structured ST@Al₂ O₃ Enables Functional PE Separator with Enhanced Lewis Acid Sites for High-Performance...

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 SiO₂ @Al₂ O₃ particles (denoted as ST@Al₂ O₃ -PE) with strong Lewis acid property and uniform porous structure on one side of the PE separator. On the other hand, ST@Al₂ O₃ 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@Al₂ O₃ can tune Li plating/stripping behavior and stabilize the lithium metal anode. The ST@Al₂ O₃ -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@Al₂ O₃ -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@Al₂ O₃ -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.