Influence of lithium salt addition on ionic conductivity and transporting properties of lithium bis(trifluoromethanesulfonyl)imide-doped glycine-based ionic liquid electrolyte

• A glycine-based ionic liquid [MGlyA][TFSI] has been prepared and characterized.
• The addition of LiTFSI in the ILs induces a conductivity decrease and ion association increases.
• Stokes–Einstein relationship in neat IL and LiTFSI-doped IL is studied.
• The lithium ionic transference numbers increase with increasing LiTFSI mole fraction in ILs.
• Walden plot is used to appreciate the ionicity in IL and LiTFSI mixtures.

The effects of the incorporation of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) on the ionic transporting and physicochemical properties of a glycine-based ionic liquid (IL) are studied. The ionization conditions of each ionic species in LiTFSI-doped glycine-based ionic liquid electrolytes ([MGlyA][TFSI]), are characterized by diffusion coefficients of the species measured using the pulsed gradient spin-echo (PGSE) NMR technique. Temperature-dependent viscosity, ionic conductivity, molar conductivity, and self diffusion coefficient in neat [MGlyA][TFSI] and LiTFSI-doped [MGlyA][TFSI] followed the Vogel–Tamman–Fulcher equation at all concentrations. The experimental molar conductivity (Λ) of neat [MGlyA][TFSI] and LiTFSI-doped [MGlyA][TFSI] is lower than that of the calculated molar conductivity (ΛNMR) from PGSE NMR technique over the entire temperature range, demonstrating that not all the diffusive species contribute to the ionic conduction, that is, free-ions, ionic pairs, and/or clusters coexist in ILs.