Mechanism of polysulfide dissolution suppression in Lithium-sulfur batteries using a novel fluorinated ether electrolyte

Lithium-sulfur (Li-S) batteries are a promising high-energy-density storage technology, yet their practical application is hindered by the dissolution of lithium polysulfides (Li₂S ₓ , 1 ≤ x ≤ 8) and the resulting shuttle effect. In this study, we demonstrate a novel electrolyte solvent, 1,1,1-trifluoro-2- (2-methoxyethoxy)ethane (C14), designed to suppress Li₂S ₓ dissolution through steric and electronic modulation. Electrochemical measurements revealed that the Li-S cell using the C14-based electrolyte operated reversibly without the infinite charging plateau characteristic of the shuttle effect, which was observed in a conventional 1,2-dimethoxyethane (DME)-based system. Mechanistic investigations combining FT-IR, Raman spectroscopy, and COSMO-RS calculations indicated that the electron-withdrawing trifluoromethyl group in C14 causes a delocalization of the molecular surface charge and restricts the conformational flexibility required for Li⁺ chelation. Crucially, S K-edge X-ray Absorption Near Edge Structure (XANES) analysis provided direct evidence of the solvation mechanism: while the DME system exhibited a pre-edge feature at 2470.3 eV attributed to Li defects generated by Li₂S ₓ ionization, this feature was notably absent in the C14 system. These results confirm that C14 effectively prevents the ionization and subsequent leaching of Li₂S ₓ into the electrolyte. This work establishes that suppressing solvent-induced ionization via charge delocalization is a vital strategy for realizing stable, high-performance Li-S batteries.