## 3 Results
### Electrochemical Stability  
In battery application, the stability of electrolytes in a wide electrochemical window is an important factor. The electrochemical stability of the prepared electrolytes was tested by linear sweep voltammetry (LSV) and cyclic voltammetry (CV). Since the ionic conductivity values of **ZN**-0.1 and **ZN**-0.15 are very similar, the electrochemical stability study was only performed for **ZN**-0.05 and **ZN**-0.1 electrolytes. Figures 5 and 6 show, respectively, the linear sweep voltammograms and cyclic voltammograms of PEG-based electrolytes containing various amount of **ZN** zwitterion. As it can be seen, all investigated compounds present quite similar profiles during both electro-oxidation and electro-reduction processes.  
Figure 5: Linear sweep voltammograms of three-electrode cells with LiTFSU/PEGDM electrolytes containing various amount of **ZN** zwitterion. Testing conditions: 25 \({}^{\circ}\)C; scan rate 1 mV s\({}^{-1}\); counter and reference electrodes—Li metal (50 \(\upmu\)m); working electrode—polished stainless steel. The inset is a zoom in between current 0 and 0.2 mA cm\({}^{-2}\).  
Figure 6: Cyclic voltammograms (first scan) of three-electrode cells with LiTFSU/PEGDM electrolytes containing various amount of **ZN** zwitterion. Testing conditions: 25 \({}^{\circ}\)C; scan rate 1 mV s\({}^{-1}\); counter and reference electrodes—Li metal (50 \(\upmu\)m); working electrode—polished stainless steel.  
The oxidative degradation of all compounds presents a unique defined on-set electrode potential. The oxidation limit of LiTFSI/PEGDM was 4.0 V at 25 \({}^{\circ}\)C which is consistent with other reported values of PEO based electrolytes [9] but that is lower than that reported by [PERSON] et al. [21] in the same electrolyte system but with higher lithium salt concentration. The presence of only 0.05 mole fraction of **ZN** in the electrolytes' formulations is able to notably improve the electrochemical stability of LiTFSI/PEGDM-based electrolytes. Indeed, the anodic limit of LiTFSI/PEGDM/**ZN** mixtures shifts to values higher than 4.5 V vs. Li\({}^{+}\)/Li. Several reports showed that the electrochemical stability of oligomer and polymer electrolytes was improved by addition of zwitterions [19; 20; 21]. This improvement is the result of the formation of a zwitterion stable layer on electrode surface that prevents the PEGDM and TFSI anion to approach to the electrode.  
The CV study of the electrolytes (Figure 6) shows that all compounds go through similar reduction processes. In principle, it can be seen that Li deposition/stripping process is quite reversible for all investigated electrolytes. Generally, organic molecules having a nitrile group, as in **ZN**, can exhibit reductive reaction at potential above 0 V vs. Li\({}^{+}\)/Li due to the polymerization of the nitrile group. In the present study, the reduction peak of **ZN**-0.05 and **ZN**-0.1 is observed at 0.35 V and 0.42 V vs. Li\({}^{+}\)/Li, respectively. In the literature, the reduction of 3-(phenylsulfonyl)propionitrile as the electrolyte additive added to carbonate-based liquid electrolyte was reported at 0.8 V vs. Li\({}^{+}\)/Li [30].