## 3 Results and Discussion
### Broadband Dielectric Spectroscopy  
Dielectric measurements were carried out upon cooling, taking advantage of the supercooling effect in these samples, pointed out in the previous Section 3.1, avoiding phase transition in this study. Figure 5a shows the ionic conductivity, determined from the imaginary part of the dielectric constant against frequency, of binary mixtures with EC against the molar fraction of ionic liquid at different temperatures. Table 4 shows the ionic conductivity values of the studied systems. A clear maximum at a molar fraction of approximately 0.15 is observed for the binary mixtures, which smoothly decreases \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample** & \(T_{\text{onset}}\) & \(T_{\text{endset}}\) & \(W_{\text{onset}}\) & \(T_{\text{peak}}\) \\ \hline \multicolumn{5}{c}{Mixtures (1 \(-\) x) EC + x [C\({}_{3}\)C\({}_{1}\)Pyrr][TFSI]} \\
0.7 & 136/436 & 194/465 & 98/72 & 182/458 \\
0.5 & 135/435 & 198/468 & 97/66 & 175/455 \\
0.15 & 144/430 & 196/466 & 89/36 & 178/454 \\
0.1 & 148/424 & 197/465 & 86/28 & 182/453 \\ \multicolumn{5}{c}{Ternary mixtures ([C\({}_{3}\)C\({}_{1}\)Pyrr][TFSI]/EC/LiTFSI)} \\
0.2 m & 138/436 & 200/478 & 96/66 & 172/458 \\
0.5 m & 133/432 & 204/478 & 95/68 & 174/458 \\
1 m & 138/428 & 210/480 & 95/73 & 176/478 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Characteristic thermogravimetric properties (temperatures in \({}^{\circ}\)C and \(W_{\text{onset}}\) in %) of binary and ternary studied systems obtained from TGA curves. as the amount of ionic liquid increases. Although viscosity grows with the IL molar fraction [25; 36], the initial rise in conductivity at low concentrations is attributed to the increase in the number of charge carriers up to \(\chi_{\rm{IL}}=0.15\). Then, the formation of ion aggregates and the increase in viscosity lead to a gradual decrease in the ionic conductivity with the IL concentration [37; 38]. This behaviour is typical of IL and carbonate mixtures, as observed by other authors [39]. It is related to the fact that while EC--a solid organic solvent at room temperature--is not ionically conductive, its high dielectric constant favors the dissociation of the ions from the ionic liquid, thereby enhancing ionic conductivity of mixtures. Figure 5: **(a)** Ionic conductivity of binary mixtures [C\({}_{3}\)C\({}_{1}\)Pyrr][TFSI] and EC against the molar fraction of IL at different temperatures. **(b)** Bahe–[PERSON] representation of the ionic conductivity at T = 298.15 K. The dashed line represents the universal curve, while the solid line includes an additional term to compute high concentration contributions. **(c)** Ionic conductivity of some molar fraction binary mixtures [C\({}_{3}\)C\({}_{1}\)Pyrr][TFSI] and EC and **(d)** LiTFSI ternary mixtures with EC:[C\({}_{3}\)C\({}_{1}\)Pyrr][TFSI] 0.50.5 molar fraction against temperature. The solid line represents the fit to the VFT equation. Similar conductivity values were found by [PERSON] et al. [33] for imidazolium and ammonium-based systems using the same lithium salt. To our knowledge, scarce previous studies analysing the transition temperatures, thermal stability, and ionic conductivity of ternary mixtures IL + carbonate + lithium salt for energy storage applications can be found in the literature. Among them, the works of [PERSON] et al. [33] and [PERSON] et al. [36] can be highlighted. In the first case, the authors report changes in different properties of ammonium- and imidazolium-based ILs (with the [TFSI]\({}^{-}\) anion moiety) upon the addition of EC cosolvent to prepare the electrolyte solution for lithium-ion battery, observing an enhancement of ionic conductivity and ion mobility related to the decrease in electrolyte viscosity. The work of [PERSON] et al.