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

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 ¹H, ⁷Li, and ¹⁹F 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 T•^-1, demonstrating that the Stokes-Einstein equation holds for the ionic diffusivity in the binary system. NMR T₁ relation time measurements show the ¹H-T₁ and ¹⁹F-T₁ 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 ¹H and ¹⁹F 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].