Dielectric Constant Guided Solvation Structure Design for Stable Solid Electrolyte Interphase in Lithium Metal Batteries

Lithium metal batteries (LMBs) are regarded as one of the most promising candidates for next‐generation energy storage systems owing to their exceptionally high theoretical energy density and low redox potential. However, their practical implementation remains severely limited by the instability of the solid electrolyte interphase (SEI), which arises from the intrinsic chemical reactivity of lithium metal with electrolyte components. To elucidate the molecular origins of SEI instability and identify electrolyte design principles, we employed a microscopic approach combining density functional theory and ab initio molecular dynamics simulations. Three typical linear organic solvents—namely dimethyl carbonate, ethyl acetate, and 1,2‐dimethoxyethane—were systematically examined to represent carbonate‐, ester‐, and ether‐based electrolytes. Our results reveal that the solvent dielectric constant critically governs both Li + solvation strength and the frontier molecular orbital energies of the salt anion, thereby determining interfacial reduction pathways. Based on these insights, we propose an optimal dielectric constant window that simultaneously balances solvation capability and reduction stability. This work establishes the solvent dielectric constant as a physically meaningful descriptor that links molecular‐scale solvation chemistry with macroscopic electrochemical performance, offering a rational design strategy for stable and efficient electrolytes in LMBs.