Over the past decade, lithium metal has been considered the most attractive anode material for high-energy-density batteries. However, its practical application has been hindered by its high reactivity with organic electrolytes and uncontrolled dendritic growth, resulting in poor Coulombic efficiency and cycle life. In this paper, we propose a design strategy for interface engineering using a conversion-type reaction of metal fluorides to evolve a LiF passivation layer and Li-M alloy. Particularly, we propose a LiF-modified Li-Mg-C electrode, which demonstrates stable long-term cycling for over 2000 h in common organic electrolytes with fluoroethylene carbonate (FEC) additives and over 700 h even without additives, suppressing unwanted side reactions and Li dendritic growth. With the help of phase diagrams, we found that solid-solution-based alloying not only facilitates the spontaneous evolution of a LiF layer and bulk alloy but also enables reversible Li plating/stripping inward to the bulk, compared with intermetallic compounds with finite Li solubility.
Keywords: alloying type; binary phase diagram; conversion reaction; fluorinated interphase; lithium metal batteries.