Understanding Lithium‐ion Transport in Sulfolane‐ and Tetraglyme‐Based Electrolytes Using Very Low‐Frequency Impedance Spectroscopy

With the increasing interest in highly concentrated electrolyte systems, correct determination of cation transference number is important. Pulsed‐field gradient NMR technique, which measures self‐diffusion coefficients, often applied on liquid electrolytes because wide accessibility and simple sample preparation. However, since assumptions this that is, complete salt dissociation, all ions participating motion, them moving independently, no longer hold true solutions, numbers, thus obtained are over‐estimated. In present work, impedance spectroscopy at a frequency range 1 MHz to 0.1 mHz was used examine concentration effect lithium‐ion under anion‐blocking conditions for two electrolytes: lithium bis(fluorosulfonyl)imide (LiFSI) sulfolane (SL) bis(trifluorosulfonyl)imide (LiTFSI) tetraglyme (G4). The former almost an order magnitude higher than latter. It also appeared increase with while latter followed opposite trend. faster Li + transport SL system attributed formation structure consisting extended chains/bridges molecules anions, facilitate cation‐hopping/ligand‐exchanged‐typed diffusion mechanism by partially decoupling cations from anions solvent molecules. G4 system, contrast, dominated long‐lived, stable [Li(G4)] solvation cages results sluggish transport. difference between mechanisms discussed via comparison bulk ionic conductivity, viscosity, ion Onsager coefficients.