Synthesis and Use of Zwitterion Bearing Sulfonyl(trifluoromethane syllonyl)imide Anion as Additive for Polymer Electrolytes  
[PERSON]  
1 CIDETEC, Basque Research and Technology Alliance (BRTA), Po. Miramon 196, 20014 Donostia-San Sebastian, Spain; [EMAIL_ADDRESS] (E.F.); [EMAIL_ADDRESS] (A.K.)  
[PERSON]  
1 CIDETEC, Basque Research and Technology Alliance (BRTA), Po. Miramon 196, 20014 Donostia-San Sebastian, Spain; [EMAIL_ADDRESS] (E.F.); [EMAIL_ADDRESS] (A.K.)  
[PERSON]  
2 CNRS, Institut de Chimie Radicalaire, UMR 7273, Aix Marseille University, 13013 Marseille, France;  
[EMAIL_ADDRESS]  
[PERSON]  
Zwitterions (ZIs) are organic molecules that contain the same number of cations and anions covalently bonded together. They possess unique properties reflecting those of ionic liquids, including non-volatility as well as thermal and electrochemical stabilities. Owning to their dipole structure, zwitterions can enhance the dissociation and mobility of lithium ions and hence increase the ionic conductivities of various lithium-based electrolyte systems. For example, [PERSON] et al. [18] observed a positive effect in ionic conductivity and lithium ion transference number after the addition of 1-ethylimidazol-3-\(n\)-propane (or butane)sulfonate to a neutral polymer. [PERSON] et al. [19] also reported that the ionic conductivity of a lithium methyl acrylate copolymer, a single-ion conducting electrolyte, was increased from 1.6 \(\times\) 10\({}^{-4}\) to 5.6 \(\times\) 10\({}^{-4}\) S cm\({}^{-1}\) at 30 \({}^{\circ}\)C after adding 1-ethylimidazol-3-\(n\)-butanesulfonate zwitterion. On the other hand, [PERSON] and coworkers recently showed that the addition of 5.5 wt% of ZIs improved the oxidation limit of oligoether-based electrolytes as well as the charge/discharge cycle stability of their Li/LCO cells [20; 21; 26]. These numerous reports show without a doubt the significant improvement of the electrochemical performance of electrolytes by the introduction of ZI structures, although the current understanding of zwitterion interactions with different species of lithium-based electrolytes is quite limited. [PERSON] et al. [27] systematically investigated the effect of cation and anion nature as well as the spacer chain length on the electrochemical properties of ZI-lithium salt mixtures. They showed that the cation's structure affects the ionic conductivity and the formation of an ionic liquid-like domain, as does the spacer-chain length, whereas the anion structure affects both ionic conductivity and transference number of carrier cations. Based on their studies, imidazolium cation is considered as the most suitable cation while (sulfonyl)imide-type anion has a significant effect on the mobility of carrier cations. [PERSON] et al. [23] recently reported that the addition of ZIs, bearing a sulfonate group, to ionic liquid/lithium salt mixtures used for battery application did not improve the overall electrochemical properties of the electrolytes. By considering these results, ZIs with negative group should link less strongly to lithium ions for improving the performance of ZIs as ion conductive materials. However, almost all studies on ZIs as conductive materials considered ZI molecules bearing either sulfonate or carboxylate groups. To our knowledge, there is no study reporting the use of ZI molecules possessing both cationic imidazolium and anionic (sulfonyl)imide groups.  
The motivation of our work is thus the synthesis of a new ZI molecule bearing both an imidazolium cation and a sulfonyl(trifluoromethane sulfonyl)imide anion site and its use as an electrolyte additive for lithium batteries. In order to improve the oxidation resistance of PEO, the new ZI molecule was added to the electrolyte mixture containing lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) and poly(ethylene glycol)dimethyl ether of 1000 g mol\({}^{-1}\).