Physicochemical Properties of Binary Ionic Liquid–Aprotic Solvent Electrolyte Mixtures

The properties of mixtures of ionic liquids (ILs) with a variety of different aprotic solvents have been examined in detail. The ILs selectedbis­(trifluoromethanesulfonyl)­imide (TFSI^–) salts with <i>N</i>-methyl-<i>N</i>-pentylpyrrolidinium (PY₁₅⁺), -piperidinium (PI₁₅⁺), or -morpholinium (MO₁₅⁺) cationsenabled the investigation of how cation structure influences the mixture properties. This study includes the characterization of the thermal phase behavior of the mixtures and volatility of the solvents, density and excess molar volume, and transport properties (viscosity and conductivity). The mixtures with ethylene carbonate form a simple eutectic, whereas those with ethyl butyrate appear to form a new IL–solvent crystalline phase. Significant differences in the viscosity of the mixtures are found for different solvents, especially for the IL-rich concentrations. In contrast, only minor differences are noted for the conductivity with different solvents for the IL-rich concentrations. For the solvent-rich concentrations, however, substantial differences are noted in the conductivity, especially for the mixtures with acetonitrile

Anion Coordination Interactions in Solvates with the Lithium Salts LiDCTA and LiTDI

Lithium 4,5-dicyano-1,2,3-triazolate (LiDCTA) and lithium 2-trifluoromethyl-4,5-dicyanoimidazole (LiTDI) are two salts proposed for lithium battery electrolyte applications, but little is known about the manner in which the DCTA^– and TDI^– anions coordinate Li⁺ cations. To explore this in depth, crystal structures are reported here for two solvates with LiDCTA(G2)₁:LiDCTA and (G1)₁:LiDCTAwith diglyme and monoglyme, respectively; and seven solvates with LiTDI(G1)₂:LiTDI, (G2)₂:LiTDI, (G3)₁:LiTDI, (THF)₁:LiTDI, (EC)₁:LiTDI, (PC)₁:LiTDI, and (DMC)_1/2:LiTDIwith monoglyme, diglyme, triglyme, tetrahydrofuran, ethylene carbonate, propylene carbonate, and dimethyl carbonate, respectively. These latter solvate structures are compared with the previously reported acetonitrile (AN)₂:LiTDI structure. The solvates indicate that the LiTDI salt is much less associated than the LiDCTA salt and that the ions in LiTDI, when aggregated in solvates, have a very similar TDI^–···Li⁺ cation mode of coordination through both the anion ring and cyano nitrogen atoms. Such coordination facilitates the formation of polymeric ion aggregates, instead of dimers. Insight into such ion speciation is instrumental for understanding the electrolyte properties of aprotic solvent mixtures with these salts