A Tertiary Amine‐Based Electrolyte with Methylation‐Mediated Steric and Electronic Synergy for High‐Performance Lithium Metal Batteries

Abstract The application of the amine‐based solvents (AS) in lithium metal batteries (LMBs) electrolyte is hindered by the severe parasitic reactions between active hydrogen and Li metal. In this study, we synthesized a methylated AS (N, N‐dimethylurethane, NDMUE), by replacing the reactive hydrogen with a methyl group. We further demonstrated its performance as a single‐component solvent for LMB electrolytes. Its performance as a single‐component solvent for LMB electrolytes was demonstrated. The methyl substitution was found to enhance steric hindrance and introduce a hyper‐conjugated structure, Its weak solvent ─Li + interactions promote anion‐dominated solvation, and facilitating controlled solvent reduction. This molecular modification leads to a mechanically robust bilayer solid electrolyte interphase (SEI) on the lithium metal anode through the sequential reduction processes: the anion‐driven reduction produced an inner inorganic layer, while the ester moiety contributed to an outer organic layer. Together, these layers effectively suppressed dendrite growth. As a result, we demonstrated outstanding cycling performance with a 3‐Ah LiFePO 4 ||Li pouch cell using the NDMUE‐based electrolyte, retaining nearly 100% of its capacity after 273 cycles at 0.2 C. This work establishes a rational design strategy for amine‐derived electrolytes and provides a fundamental framework for developing advanced electrolyte systems in durable LMBs.