Thermophysical Characterization of TFSI Based Ionic Liquid and Lithium Salt Mixtures

Abstract

The ionic liquids (ILs) doped with metal salts have become a real alternative as electrolytes for batteries, but the right choice of these compounds for reaching the adequate properties and performance is still a challenge, and strategies are therefore needed for achieving it. The thermophysical properties of IL 1-butyl-1-methylpyrrolidinium bis[(trifluoromethyl)sulfonyl]imide ([bmpyr] [TFSI]) and its mixture with bis-(trifluoromethane)-sulfonimide lithium salt (from 0.1 m to saturation level) were determined in this work. These properties are density (ρ), speed of sound (U), and corresponding derived magnitudes, such as the bulk modulus and the thermal coefficient, as well as electrical conductivity (σ) against temperature. Density shows a linear decreasing dependence with temperature and a clear increase with the addition of salt, whereas the thermal expansion coefficient increases with temperature and salt addition. Speed of sound decreases with both temperature and salt concentration, and the adiabatic compressibility calculated by means of the well-known Laplace equation increases, as expected, with temperature in all the studied cases, although a small variation with concentration was observed. Electrical conductivity increases with temperature following the Vogel-Fulcher-Tammann (VFT) equation and decreases with the addition of salt.

Ionotronics for reverse actuation

“…The liquid was considered to be practically incompressible for the pressures applied here, which are much smaller than the bulk moduli of ionic liquids that are of the order of GPa. 29 Thus, the volume of the droplet, Ω , is conserved and calculated as…”

Pyrrolidinium Containing Ionic Liquid Electrolytes for Li-Based Batteries

“…Similarly to C3mpyr-based ILs, there has been extensive characterization of 1-butyl-1methylpyrrolidinium (C4mpyr)-based ILs [147], for example, Fernández-Miguez et al [115] Al 2 O 3 has been investigated as a protective agent for Li metal and has mainly been studied from the perspective of surface coating and plating technologies. Wen et al [174] utilized a leaf-like Al 2 O 3 skeleton to form a quasi-solid-state electrolyte comprising of 1 M LiTFSI, and C 3 mpyrTFSI.…”

“…They can be tuned to exhibit low volatility coupled with high ionic conductivity and electrochemical and thermal stability. It is therefore possible to design electrolytes, for specific applications such as, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, which exhibits high lithium ionic conductivity (3 mS cm −1 ) at room temperature for energy storage [ 115 ].…”

“…Similarly to C 3 mpyr-based ILs, there has been extensive characterization of 1-butyl-1-methylpyrrolidinium (C 4 mpyr)-based ILs [ 147 ], for example, Fernández-Miguez et al [ 115 ] investigated high (1.5 M) and low (0.1 M) LiTFSI salt concentrations within C 4 mpyrTFSI ILs. It was determined that LiTFSI salt addition leads to higher densities than that of the pure IL, but it decreased linearly with increasing temperature.…”