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

Abstract

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.