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

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, Li₂O, Li₃N, Li₂S, 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.