Viscosity and carbon dioxide solubility for LiPF6, LiTFSI, and LiFAP in alkyl carbonates: lithium salt nature and concentration effect.

In this paper, we have reported the CO2 solubility in different pure alkyl carbonate solvents (EC, DMC, EMC, DEC) and their binary mixtures as EC/DMC, EC/EMC, and EC/DEC and for electrolytes [solvent + lithium salt] LiX (X = LiPF6, LiTFSI, or LiFAP) as a function of the temperature and salt concentration. To understand the parameters that influence the structure of the solvents and their ability to dissolve CO2, through the addition of a salt, we first analyzed the viscosities of EC/DMC + LiX mixtures by means of a modified Jones-Dole equation. The results were discussed considering the order or disorder introduced by the salt into the solvent organization and ion solvation sphere by calculating the effective solute ion radius, rs. On the basis of these results, the analysis of the CO2 solubility variations with the salt addition was then evaluated and discussed by determining specific ion parameters Hi by using the Setchenov coefficients in solution. This study showed that the CO2 solubility has been affected by the shape, charge density, and size of the ions, which influence the structuring of the solvents through the addition of a salt and the type of solvation of the ions.