Engineering Solid Electrolyte Interphase in Lithium Metal Batteries by Employing an Ionic Liquid Ether Double-Solvent Electrolyte with Li[(CF₃SO₂)(<i>n</i>‑C₄F₉SO₂)N] as the Salt

An ionic liquid ether double-solvent electrolyte, comprising 1 M Li­[(CF3SO2)­(n-C4F9SO2)­N] dissolved in N-propyl-N-methylpiperidinium bis­(fluorosulfonyl)­imide/1,3-dioxolane (1:1, v/v), is utilized to tackle uncontrollable dendrite growth and unsatisfactory Coulombic efficiency, which are two main barriers for commercial adoption of rechargeable lithium metal batteries. X-ray photoelectron spectroscopy analysis reveals that a highly conductive (Li3N), highly flexible (polydioxolane and F-containing organic compounds) solid electrolyte interphase film formed on the lithium metal anode. In this recipe, Li|Cu cells can operate ca. 1400 cycles with a high average Coulombic efficiency of 98.2% at 10 mA cm–2, and, moreover, Li|LiFePO4 cells can run 1000 cycles with a capacity fading less than 3% at 1 C