Rational Design of Asymmetric Lithium Salts with Multi‐Functional Capabilities for Stable Lithium Metal Batteries

Abstract

Abstract Lithium metal batteries (LMBs) face severe interfacial instability in carbonate‐based electrolytes, where solvent‐centric solvation structures drive the formation of fragile, organic‐rich solid–electrolyte interphases (SEIs). However, existing strategies mainly rely on solvent engineering, whereas lithium salt design remains underexplored. Herein, we design an asymmetric lithium salt, lithium (N, N‐dimethylsulfamoyl) (trifluoromethanesulfonyl)imide (LiDMTFSI), featuring an electron‐donating dimethylamino group that enhances the anion's nucleophilicity and Lewis basicity. By introducing a push‐pull effect on the anionic charge, LiDMTFSI shifts the solvation structure from solvent‐rich to anion‐rich, thereby facilitating the co‐dissolution of beneficial lithium salt. The resulting solvent‐deficient solvation sheath governs the interphasial chemistry to favor the formation of a compact inorganic‐rich SEI (e.g., LiF, Li 2 O, Li 3 N, Li 2 S, and other beneficial components) with excellent mechanical integrity and interfacial ion transport, enabling uniform Li deposition and mitigating parasitic side‐reactions. A high Li plating/stripping Coulombic efficiency of 99.1% was achieved in dilute carbonate‐based electrolytes, and full cells with ultrathin Li anodes and high‐loading NMC811 cathodes demonstrated consistent operation for over 120 cycles with 83% capacity retention at a high voltage of 4.3 V. These findings underscore the potential of anion molecular design as a powerful strategy for interphasial engineering in high‐energy LMBs.