Heteroatom-tuned weakly solvating electrolyte with good wettability enriching solid electrolyte interphase chemistry toward stable lithium metal batteries

Weakly solvating electrolytes (WSEs) promote the formation of anion-driven solid electrolyte interphases (SEI), enabling stable lithium metal batteries. However, current strategies involving alkylated modification, steric hindrance incorporation, coordinated oxygen (O) regulation, and selective fluorination face poor-diversity interfacial chemistry, high cost, or environmental concerns. Here, we propose a heteroatom-substitution strategy to design a WSE composed of lithium bis(fluorosulfonyl)imide (LiFSI) and 1,4-oxathiane (OTA) as a single solvent. Substituting oxygen with sulfur in conventional 1,4-dioxane (1,4-DX) generates OTA with a modulated dipole and charge distribution, weakening Li+-OTA coordination while promoting anion-involved solvation sheath. This unique solvation structure triggers the formation of an inorganic-rich SEI with sulfur-containing species, enabling high Li plating/stripping coulombic efficiency and stable Li||Li symmetric cells cycling for 1000 h. Benefiting from the superior interfacial chemistry and wettability of the electrolyte to the LiFePO4 cathode, full cells exhibit exceptional cycling stability even at low negative-to-positive (N/P) ratios. A pouch cell coupled with 3.58 mAh cm−2 LiFePO4 and 20 μm Li (N/P ∼1.15) maintains 88.77 % capacity after 150 cycles. This work shows a fluorine-free solvent design paradigm for advanced WSEs, providing novel insights toward stable LMBs.