Viscosity and Carbon Dioxide Solubility for LiPF6, LiTFSI, and LiFAP in Alkyl Carbonates: Lithium Salt Nature and Concentration Effect

International audienceIn 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

Physical Properties of a New Deep Eutectic Solvent Based on a Sulfonium Ionic Liquid as a Suitable Electrolyte for Electric Double-Layer Capacitors

International audienceWe present in this study the physical properties of two deep eutectic solvent (DES) mixtures based on solid sulfonium bis[(trifluoromethyl)sulfonyl]imide (S111TFSI) aprotic ionic liquid and two different H-bond donors, formamide (FMD) and trifluoroamide (TFA), according to temperature. First, we investigated their thermal properties by differential scanning calorimetry , and the results revealed the formation of a deep eutectic solvent giving a wide liquid range from −40 to 270 °C for these mixtures which froze at a much lower temperature than either of the individual components. The densities, ionic conductivities, and viscosities of these DESs were measured according to temperature and then discussed by applying Arrhenius or Vogel–Tamman–Fulcher (VTF) equations, as well as the Walden classification. Thanks to their favorable transport properties, both S111TFSI/TFA and S111TFSI/FMD mixtures contribute to the formulation of the electrolytes with 1 mol·L–1 LiTFSI. The performances of these electrolytes were then estimated by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge/discharge for activated carbon electrochemical double layer capacitor applications at 80 °C. The results showed that the selected H-bond donors allowed ion dissociation without solvation, increasing micropore accessibility and giving high capacitance values up to 350 F·g–1 in the case of formamide-based DESs. These unusual performances of the activated carbon material are debated with regards to the activation energy barrier to access the microporosity by ions in sulfonium-amides DESs

Comparative Study of Alkali‐Cation‐Based (Li + , Na + , K + ) Electrolytes in Acetonitrile and Alkylcarbonates

International audienceThe development of a suitable functional electrolyte is urgently required for fast-charging and high-voltage alkali-ion (Li, Na, K) batteries as well as next-generation hybrids supercapacitors. Many recent works focused on an optimal selection of electrolytes for alkali-ion based systems and their electrochemical performance but the understanding of the fundamental aspect that explains their different behaviour is rare. Herein, we report a comparative study of transport properties for LiPF6 , NaPF6 , KPF6 in acetonitrile (AN) and a binary mixture of ethylene carbonate (EC), dimethyl carbonate (DMC): (EC/DMC : 1/1, weigh) through conductivities, densities and viscosities measurements in wide temperature domain. By application of the Stokes-Einstein, Nernst-Einstein, and Jones Dole equations, the effective ionic solvated radius of cation (r eff ), the ionic dissociation coefficient (α D ) and structuring Jones Dole's parameters (A, B) for salt are calculated and discussed according to solvent or cation nature as a function of temperature. From the results, we demonstrate that better mobility of potassium can be explained by the nature of the ion-ion and ion-solvent interactions due to its polarizability. In the same time, the predominance of triple ions in the case of K+ , is a disadvantage at high concentration