Solid-Liquid Equilibria Measurements of Mixtures of Lithium Bis(trifluoromethanesulfonyl)imide with Varying Alkyl Chain Length Ammonium Bis(trifluoromethanesulfonyl)imide Ionic Liquids

Ionic liquid (IL)-metal mixtures are potential solvents for a variety of applications, including metal electrodeposition, electrolytes for batteries, catalysis, and for separations processes involving liquid liquid extraction. The solubility of a metal in an IL is fundamentally important to selecting an appropriate IL for a potential process; however, relatively few measurements have been reported in the literature. The solid-liquid equilibria of binary mixtures of lithium bis(trifluoromethanesulfonyl)imide and three ammonium bis(trifluoromethanesulfonyl)imide ILs are investigated. Measurements are made through two different methods. A visual method allows direct observation of the phase behavior between room temperature and 373 K and a differential calorimetry method provides solid liquid equilibria information up to 623 K. The activity coefficients of the solid in the liquid are calculated from the measured phase equilibria and the pure component physical properties. The mutual solubilities of lithium bis(trifluoromethanesulfonyl)imide and hexadecyl-trimethylammonium bis(trifluoromethanesulfonyl)imide are found to be higher than expected given the long alkyl chain length of the IL cation.