Influence of LiTFSI Addition on Conductivity, Diffusion Coefficient, Spin–Lattice Relaxation Times, and Chemical Shift of One-Dimensional NMR Spectroscopy in LiTFSI-Doped Dual-Functionalized Imidazolium-Based Ionic Liquids

Abstract

An ionic liquid (IL) 1-allyl-3-(2-methoxyethyl)imidazolium bis(trifluoromethylsulfonyl)imide ([AMO][TFSI]) is prepared, and the effect of the addition of LiTFSI into [AMO][TFSI] on the transport and physicochemical properties is studied herein. The diffusion coefficients of 1 H, 7 Li, and 19 F are determined using pulsed-gradient spin−echo NMR to study the dynamics of all ion species. The neat [AMO][TFSI] and LiTFSI-doped [AMO][TFSI] give approximately straight lines for the relationship of D vs Tη −1 , demonstrating that the Stokes−Einstein equation holds for the ionic diffusivity in the binary system. NMR T 1 relation time measurements show the 1 H-T 1 and 19 F-T 1 of LiTFSI-doped [AMO] [TFSI] decrease with the increase of Li salt concentration, which is due to the viscosity increases and the formation of stable coordination adducts of Li and TFSI when the salt concentration increases. From the study of chemical shift in one-dimensional NMR spectroscopy, an upfield shift in 1 H and 19 F spectra is observed in ILs with increasing lithium salt concentration; the formation of ion clusters is the dominant effect after the addition of LiTFSI in [AMO] [TFSI].

Origin of Unusual Acidity and Li+ Diffusivity in a Series of Water-in-Salt Electrolytes

“…This observation strongly suggests the existence of free volume space (such as ion diffusion channels) for the independent diffusion of ions even at higher LiTFSI concentrations. It should be noted that D Li is always higher than D TFSI in the LiTFSI/H 2 O solutions, which pronouncedly differs from nonaqueous electrolyte solutions, where slower cation diffusion ( D anion > D Li ) is widely reported. ,− Such behavior is either due to the formation of clumsy Li + primary solvation sheaths, which have slower movement as compared with anions at dilute salt concentrations, or due to the formation of a contact-ion pair based Li + -ion cluster: [Li­(TFSI) m +1 ] m ‑ at high salt concentrations, where the maximum value of m + 1 = 4 in the mixture . Hence it is reasonable to assume that the variation of relative diffusion coefficients among Li + , TFSI – , and H 2 O is closely related to the modification of Li + -solvation clusters composed of [Li­(H 2 O) l (TFSI) m +1 ] m ‑ .…”

Translational Diffusion in a Set of Imidazolium-Based Ionic Liquids [bmim]+A– and Their Mixtures with Water

“…As most species contain at least one NMR-detectable isotope, the diffusion can be studied directly without any additional labeling. Multinuclear pulsed field gradient NMR diffusometry for different imidazolium-based RTILs with varying anions was carried out, − and many diffusion investigations related to this type of ILs are devoted to [bmim] + BF 4 – . Overwhelmingly, the data for neat imidazolium-based ILs indicate that the cations diffuse almost equally to the anion, and diffusion coefficients are correlated with viscosity of corresponding ILs .…”

Molecular Mobility in a Set of Imidazolium-Based Ionic Liquids [bmim]+A– by the NMR-Relaxation Method

“…A large-scale study of the imidazolium-based ionic liquid ([AMO]­[TFSI]) was carried out in the works, , which included experiments for measuring diffusion coefficients, spin–lattice relaxation times, conductivity, viscosity, and chemical shift variations in NMR spectra. A number of investigations of the diffusion motion in ILs are devoted to [bmim] + BF 4 – .…”