A multifunctional separator with Mg(OH)2 nanoflake coatings for safe lithium-metal batteries

Dendrite growth and thermal runaway induce serious safety hazards, impeding the practical applications of lithium metal batteries (LMBs). Although extensive advances have been attained in terms of LMB safety, most work only focus on a single aspect at a time. This paper reports a multifunctional separator coated by Mg(OH)2 nanoflakes with various excellent properties including electrolyte wettability, ionic conductivity, Li+ transference number, puncture strength, thermal stability and flame retardance. When used in LMBs, the Mg(OH)2 nanoflake coatings enable uniform Li+ distributing, which makes it homogeneous to deposit lithium, realizing effective dendrite suppression and less volume expansion. Meanwhile, Mg(OH)2 coatings can ensure LMBs are in normal conditions without thermal runaway until 140 °C. A part of lithium can be converted into Li+ ions by Mg(OH)2 during repeated charge/discharge cycles, not only reducing the risk of separator damage and consequent short circuit, but also replenishing the capacity loss of LMBs. The Mg(OH)2 nanoflakes can coat on all kinds of commercial separators to improve their performances, which offers a facile but effective strategy for fabricating multifunctional separators and a comprehensive insight into enhancing LMB safety.