Steric‐Electronic Synergy in Isopropyl‐Tailored Electrolytes: Enabling Stable Interphases and Long‐Cycling Lithium Metal Batteries via Terminal Isomerization

The development of electrolytes that synergistically integrate moderate weak solvation, high oxidation stability, and low molecular weight remains a formidable challenge for lithium (Li) metal batteries (LMBs), as conventional chain-extension strategies often exacerbate ionic conductivity loss or fail to suppress α-hydrogen (α-H) oxidation. Herein, a terminal isomerization strategy is proposed to engineer 1,2-diisopropoxyethane (DIPE), an ether electrolyte featuring isopropyl termini that synergistically regulate steric-electronic effects. The branched isopropoxy groups 1) induce tailored steric hindrance to weaken Li⁺-solvent interaction (38.7% reduction vs DME), promoting anion-dominated inorganic-rich interphases; 2) reduce α-H exposure by 67% compared to linear analogs, elevating oxidative stability; and 3) maintain optimal molecular weight (MW = 136 g mol^-1) to ensure favorable ionic conductivity. When formulated into a locally high-concentration electrolyte, DIPE enables Li||Cu half-cells with 99.5% Coulombic efficiency and extends Li||NCM811 cycle life to 500 cycles (77% capacity retention), outperforming both linear (e.g., DBE) and over-branched (DtBE) counterparts. This work establishes terminal-group isomerization as a universal molecular design paradigm to reconcile interfacial stability with ionic transport in high-performance LMBs.