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

Abstract

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 MgF2 onto commercial polyethylene separator. The composite separator possesses excellent wettability and high thermal stability. When the MgF2 coating contacts Li metal anode directly, an artificial SEI layer is in-situ formed due to the spontaneously reaction of MgF2 and Li metal, which is composed of LiF and lithiophilic Mg. More importantly, a small amount of dissolved MgF2 can fill the micro-gaps between un-contact MgF2 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 MgF2 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.