## 3 Results  
### Thermal Properties  
The thermal stability of the **ZN** molecule and electrolyte solutions was characterized by using TGA. The zwitterion molecule **ZN** starts to decompose at around 280 \({}^{\circ}\)C with a maximum weight loss above 300 \({}^{\circ}\)C where a unique decomposition process causes almost 80% of weight loss. This decomposition temperature is quite similar to those reported in the literature [21,29]. Thus, we can conclude that **ZN** possesses a good thermal stability, which enable its use as electrolyte additive for battery applications. All prepared electrolytes present a good thermal stability with the maximum weight loss above 390 \({}^{\circ}\)C. The electrolytes present two decomposition events; the first one causes almost 60 wt% loss while the second one, recorded as a small shoulder at higher temperature, causes approximatively 20 wt% loss (Figure 1, Table 2). This second transition can be attributed to the degradation of LiTFSI salt. Its intensity decreases with the increasing of the zwitterion content in the formulation. While in the zwitterion there is almost no weight loss beside the main decomposition event, all electrolytes suffer a gradual weight loss due to moisture uptake by hygroscopic PEGDM and LiTFSI during the transfer of samples from the dry room to the TGA.  
DSC data show that **ZN** exhibits a T\({}_{\text{g}}\) and a T\({}_{\text{m}}\) at 12 \({}^{\circ}\)C and 166 \({}^{\circ}\)C, respectively. The T\({}_{\text{m}}\) of **ZN** is higher than that of 3-(butyldimethylammonio)propyl sulfonyl-(trifluoromethylomethane sulfonyl)imide, which is 104 \({}^{\circ}\)C [27], but lower than that observed for imidazolium-based zwitterions having a sulfonate group [29]. LiTFSI/PEGDM mixture shows a T\({}_{\text{g}}\) at -56 \({}^{\circ}\)C and a small melting peak at around 20 \({}^{\circ}\)C.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Sample** & **T\({}_{\text{g}}\)** (\({}^{\circ}\)C)** & **T\({}_{\text{m}}\)** (\({}^{\circ}\)C)** & **T at 10 wt\% Loss (\({}^{\circ}\)C)** & **DTA\({}_{\text{max}}\)** (\({}^{\circ}\)C) 1 ** \\ \hline
**ZN** zwitterion & 12 & 166 & 287 & 310 & 21 \\
**ZN**-0 & \(-\)56 & 20 & 241 & 405 & 3 \\
**ZN**-0.05 & \(-\)55 & / & 238 & 396 & 4 \\
**ZN**-0.10 & \(-\)53 & / & 245 & 397 & 6 \\
**ZN**-0.15 & \(-\)53 & / & 270 & 400 & 8 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Summary of TGA and differential scanning calorimetry (DSC) studies of the **ZN** molecule and investigated electrolytes.  
Figure 1: TGA curves of **ZN** molecule and the investigated electrolyte solutions with and without **ZN**.  
[PERSON] et al. [21] reported a T\({}_{\rm g}\) of \(-\)54 \({}^{\circ}\)C and no melting point for the same mixture but with a molar ratio of [EO]/[Li] = 8. It is well known that increasing the lithium salt concentration allows it to decrease the crystallization of PEO. All the prepared LiTFSI/PEGDM solutions containing **ZN** zwitterion show no melting point and have almost the same T\({}_{\rm g}\) values as that of LiTFSI/PEGDM (Table 2). In comparison, [PERSON] et al. [21] noted an increase of T\({}_{\rm g}\) of 9 \({}^{\circ}\)C for their sample composing of LiTFSI/PEGDM ([EO]/[Li] = 8) and 4.6 wt% of 3-(1-(2-(2-cyanoethoxy)ethyl)-1H-imidazol-3-ium-3-yl)propane-1-sulfonate zwitterion. The only difference between [PERSON]'s work and ours is the nature of the zwitterion anion sulfonate group in their study and STFSI anion in the present study. This suggests that the interaction between the STFSI anion and lithium ions is less strong, hence leading to a slight increase in the T\({}_{\rm g}\) value of electrolyte mixtures.