LiF-rich and self-repairing interface induced by MgF2 engineered separator enables dendrite-free lithium metal batteries

• A LiF-rich interface is constructed on Li metal by separator engineering. • The MgF 2 coating endows the LiF-rich interface with self-repair. • The LiF-rich s interface promotes Li nucleation and enables a dendrite-free Li deposition. • The cells with composite separators show enhanced electrochemical performances. Lithium metal batteries (LMBs) are promising for high-energy density rechargeable batteries while suffer from uncontrolled dendrites growth and unstable solid electrolyte interface (SEI) layer on the surface of lithium (Li) metal anodes. In this study, a facile and low-cost strategy is proposed to enable dendrite-free and long-life LMBs by coating MgF 2 onto commercial polyethylene separator. The composite separator possesses excellent wettability and high thermal stability. When the MgF 2 coating contacts Li metal anode directly, an artificial SEI layer is in-situ formed due to the spontaneously reaction of MgF 2 and Li metal, which is composed of LiF and lithiophilic Mg. More importantly, a small amount of dissolved MgF 2 can fill the micro-gaps between un-contact MgF 2 coating and Li anode and repair the tiny cracks in the SEI generated during repeated charge–discharge process. Hence, a continuous SEI layer is formed throughout the entire surface of Li metal anode with lithiophilic, LiF-rich and self-repairing capabilities, protecting Li metal anode, reducing the nucleation overpotential, promoting smooth Li plating and inhibiting Li dendrites growth. The Li||Li symmetric cells, Cu||Li asymmetric cells and full cells with the MgF 2 coated separators delivers significantly enhanced coulombic efficiency and cycle life in both ether-based and carbonate-based electrolyte. This design of artificial LiF-rich SEI with self-repairing capability by separator engineering paves a new insight for the application of alkali metal batteries.