A Tertiary Amine-Based Electrolyte with Methylation-Mediated Steric and Electronic Synergy for High-Performance...

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 LiFePO₄||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.