Solubilities and ionic conductivities of ionic liquids containing lithium salts

Solubilities of six lithium salts were measured at 25°C in three imidazolium-based ionic liquids: 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]), 1-Ethyl-3-methylimidazolium trifluoromethanesulfonate ([EMIM][Tf]) and 1-Butyl-3-methylimidazolium dicyanamide ([BMIM][DCA]). The lithium salts were LiTFSI, LiNO3, LiI, LiTf, LiPF6 and LiBF4. There were large differences in solubility of lithium salts depending on the anion of the salt and on the ionic liquid. The largest difference in solubility was observed for LiNO3. 7Li NMR spectra of the concentrated salt-containing ionic liquids indicate that Li+ and NO3− are strongly associated in the investigated ionic liquids. The different abilities of the ionic liquids to solubilize these associated salts could explain the solubility differences. The ionic conductivity of each salt-containing ionic liquid was measured in the temperature range 15 to 60°C up to concentrations close to the solubility limit at 25°C. The ionic conductivity of the salt-containing ionic liquid decreases with salt concentration. Changing the lithium anion had almost no influence on the conductivity in [BMIM][[DCA] but a noticeable influence on the ionic conductivity in [EMIM][TFSI]. The solubilities in [EMIM][Tf] were too small to detect the effect of the anion of the lithium salt on conductivity.