Strategy for Stable Interface in Lithium Metal Batteries: Free Solvent Derived vs Anion Derived

A variety of electrolyte engineering strategies have been introduced to extend the cycle life of lithium metal batteries (LMBs). These strategies can be largely grouped into two categories: those that induce a solvent-driven vs those that induce an anion-driven solid electrolyte interphase (SEI) layer. Although each strategy has proven to be effective for SEI manipulation, they are not yet comprehensively understood. Here, lithium salts with different dissociation abilities are systematically screened. Among those screened, highly dissociative lithium bis(trifluoromethane) sulfonimide (LiTFSI) with a high lowest unoccupied molecular orbital (LUMO) level is found to have enhanced cyclability by promoting the reduction of the solvent, fluoroethylene carbonate (FEC). Moreover, 1,2-dimethoxyethane (DME) as a cosolvent induces free FEC from the solvation sheath to further improve the cycle life by forming an SEI layer with uniformly distributed fluorine-containing components. This study unveils the usefulness of free solvent molecules by manipulating the solvation environments in achieving high-performance LMBs.