## 4 Conclusions  
In this work, the electric and thermal properties of [C\({}_{3}\)C\({}_{1}\)Pyrr][TFSI] and its binary mixtures with EC, and ternary (from the eutectic composition) mixtures with LiTFSI were studied. The main conclusions of the research are the following:  
* EC addition provokes the widening of transition peaks in DSC. In addition, melting and crystallisation take place in two steps, which indicates that salt addition and/or EC reduce, or remove, the crystalline behaviour. Binary mixture enthalpies increase with the addition of EC presenting lower values than the corresponding pure EC. * The binary mixture 0.5 [C\({}_{3}\)C\({}_{1}\)Pyrr][TFSI] + 0.5 EC corresponds to the eutectic composition whose melting temperature is the lowest of all the studied concentrations. * Salt addition to the eutectic composition removes the phase transition at high quantities of salt in the range from \(-\)80 to 100 \({}^{\circ}\)C.
* The values of conductivity of the [C\({}_{3}\)C\({}_{1}\)Pyrr][TFSI] + EC mixtures are higher than the pure IL and present a maximum at x\({}_{\rm{IL}}\) = 0.15. * LiTFSI addition to the 0.5 [C\({}_{3}\)C\({}_{1}\)Pyrr][TFSI] + 0.5 EC mixture diminishes the conductivity; however, the values at room temperature are higher than the required 0.1 S\(\cdot\)m\({}^{-1}\) for energy storage applications. \begin{table}
\begin{tabular}{c c c c} \hline
**Sample** & \(\sigma_{\infty}\)**/S m\({}^{-1}\)** & \(E_{a}\)**/eV** & \(T_{0}\)**/K** \\ \hline \multicolumn{4}{c}{Mixtures (1 \(-\) x) EC + x [C\({}_{3}\)C\({}_{1}\)Pyrr][TFSI]} \\
1 & 12.1 (17) & 0.293 (18) & 203 (13) \\
0.85 & 20.6 (59) & 0.0352 (51) & 186.0 (74) \\
0.7 & 19.8 (36) & 0.0310 (30) & 192.6 (46) \\
0.5 & 19.6 (44) & 0.0279 (38) & 191.1 (67) \\
0.4 & 19.8 (41) & 0.0282 (37) & 185.6 (68) \\
0.3 & 20.4 (42) & 0.0285 (40) & 179.7 (76) \\
0.25 & 13.0 (20) & 0.0202 (25) & 196.1 (57) \\
0.2 & 13.7 (32) & 0.0223 (42) & 186.9 (97) \\
0.15 & 11.8 (10) & 0.0179 (14) & 199.1 (34) \\  & \multicolumn{2}{c}{Ternary mixtures ([C\({}_{3}\)C\({}_{1}\)Pyrr][TFSI]/EC/LiTFSI)} \\
0.2 m & 30 (14) & 0.041 (10) & 171 (15) \\
0.5 m & 9.5 (51) & 0.0253 (82) & 203 (14) \\
1 m & 13.3 (74) & 0.0320 (81) & 203 (10) \\ \hline \end{tabular}
\end{table} 
Table 6: Fitting parameters of the VFT equation (Equation (5)) for all samples. In summary, while further studies are required to fully assess their performance and stability under operational conditions, the results obtained here present the proposal of a new promising electrolyte, consisting of a ternary mixture of the ionic liquid ([C\({}_{3}\)C\({}_{1}\)Pyrr][TTSI]), ethyl carbonate, and lithium salt. This electrolyte exhibits an excellent liquid range, characterised by the absence of crystallisation peaks and high thermal stability, while maintaining high ionic conductivity. Conceptualization, A.S.-A., J.S., and J.J.P. ; methodology, M.V., A.S.-A., J.M.S.-P., and J.J.P. ; validation, A.S.-A., J.J.P., M.V., and J.S. ; writing--original draft preparation, J.M.S.-P., R.S.E., and A.S.-A. ; writing--review and editing, A.S.-A., J.M.S.-P., R.S.E., J.J.P., M.V., and J.S. ; funding acquisition, J.J.P., M.V., and J.S. All authors have read and agreed to the published version of the manuscript. This research was founded by the Spanish Ministry of Economy and Competitiveness and FEDER Program through the project MAT2017--89239--C2--1--P and the Network Ionic Systems for energy sustainability (SISE) RED2018--102679--T, and by Xunta de Galicia through GRC ED431C 2020/10 and ED481D 2023/014 projects. Not applicable. The original contributions presented in the study are included in the article; further inquiries can be directed to the corresponding author/s. Authors acknowledge [PERSON] (RIAIDT-USC) for the technical support in DSC and TGA measurements. This work was supported by Xunta de Galicia through GRC ED431C 2024/06 project.