New lithium salts such as lithium bis(fluorosulfonyl)imide (LiFSI) and lithium 4,5-dicyano-2-(trifluoromethyl)imidazole-1-ide (LiTDI) are now challenging lithium hexafluorophosphate (LiPF _(6) ), the most used electrolyte salt in commercial Li-ion batteries. Thus it is now important to establish a comparison of these electrolyte components in a standard solvent mixture of ethylene carbonate and dimethyl carbonate (EC/DMC: 50/50 wt%). With this aim, transport properties, such as the ionic conductivity, viscosity and ~(7) Li self-diffusion coefficient have been deeply investigated. Moreover, as these properties are directly linked to the nature of the interionic interactions and ion solvation, a better understanding of the structural properties of electrolytes can be obtained. The Li salt concentration has been varied over the range of 0.1 mol L ~(?1) to 2 mol L ~(?1) at 25 °C and the working temperature from 20 °C to 80 °C at the fixed concentration of 1 mol L ~(?1) . Experimental results were used to investigate the temperature dependence of the salt ion-pair (IP) dissociation coefficient ( α _(D) ) with the help of the Walden rule and the Nernst–Einstein equation. The lithium cation effective solute radius ( r _(Li) ) has been determined using the Jones–Dole–Kaminsky equation coupled to the Einstein relation for the viscosity of hard spheres in solution and the Stokes–Einstein equation. From the variations of α _(D) and r _(Li) with the temperature, it is inferred that in EC/DMC LiFSI forms solvent-shared ion-pairs (SIP) and that, LiTDI and LiPF _(6) are likely to form solvent separated ion-pairs (S _(2) IP) or a mixture of SIP and S _(2) IP. From the temperature dependence of α _(D) , thermodynamic parameters such as the standard Gibbs free energy, enthalpy and entropy for the ion-pair formation are obtained. Besides being in agreement with the information provided by the variations of α _(D) and r _(Li) , it is concluded that the ion-pair formation process is exergonic and endothermic for the three salts in EC/DMC.
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