Synergistic Composite Coating for Separators in Lithium Metal Batteries

Despite their conspicuous advantages in energy density, lithium metal batteries (LMBs) are still in the research stage owing to uncontrolled lithium dendrite growth, which deteriorates their cycle life and safety. In this study, we aim to formulate a separator coating and identify the optimal coating conditions that are scalable with the ultimate goal of fabricating separators that largely address the chronic issues of LMBs. For this purpose, a mixture of an ionic liquid, a block copolymer, and microspheres was applied to a conventional polyethylene separator. While the polymeric microspheres mechanically strengthen the coating layer against lithium dendrite growth, the ionic liquid and block copolymer support lithium ion conduction and provide robust connections among the composite components, all jointly resulting in a uniform lithium ion flux, which in turn results in plated lithium metal with a highly compact morphology. Alongside improved thermal stability, this composite coating enables superior cyclability in Li parallel to Li symmetric and Li parallel to Cu asymmetric cells as well as pouch-type full cells. The simple, scalable nature of the present coating approach renders it useful not only for lithium metal batteries currently in development but also for common commercial lithium ion batteries, which suffer from severe lithium plating upon fast charging.