Decoupling Quasi‐Solid‐State Sulfur Conversion Mechanisms in Weakly Solvating and Locally High Concentration Electrolytes

ABSTRACT

Lithium–sulfur (Li–S) batteries offer high theoretical energy density but are constrained by polysulfide dissolution, shuttling, and sluggish conversion. Here, a weakly solvating electrolyte comprising cyclopentyl methyl ether (CME) and 1,1,2,2‐tetrafluoroethyl 2,2,3,3‐tetrafluoropropyl ether (TTE; CME–TTE) is compared with a localized high‐concentration electrolyte comprising diethylene glycol dimethyl ether (G2) and TTE (G2–TTE). Molecular dynamics (MD) simulations show that G2–TTE combines multidentate G2 coordination with appreciable bis(trifluoromethanesulfonyl)imide (TFSI ⁻ ) participation, whereas CME–TTE exhibits weaker, predominantly monodentate solvent coordination and stronger relative anion association. Galvanostatic intermittent titration technique (GITT), distribution of relaxation times (DRT), square‐wave voltammetry (SWV), shuttle‐current measurements, operando ultraviolet–visible (UV–vis) and Raman spectroscopy, physical‐property measurements, post‐cycling characterization, and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) link coordination to electrochemical behavior. Both formulations restrict extensive bulk polysulfide accumulation, but G2–TTE maintains more effective localized ion transport and interfacial conversion. G2–TTE cells consequently deliver capacities above 900 mAh g ^{− 1} after 200 cycles with nearly 100% Coulombic efficiency. A two‐cathode pouch cell delivers 600 mAh g ^{− 1} after 50 cycles at an electrolyte‐to‐sulfur ratio of 1.37 µL mg ^{− 1} . These results identify coordination connectivity, anion participation, and transport as coupled design parameters for quasi‐solid‐state Li–S batteries.