Enhancement of the electrochemical stability of tetraglyme-Li[TFSA] electrolyte systems by adding [Bimps] zwitterion: An in-situ IV-SFG study

The potential-dependent interfacial structures of Pt/tetraglyme-lithium bis(trifluoromethylsulfonyl) amide ((Pt)/G4-Li[TFSA]) systems were assessed with and without 3-(1-butyl-1H-imidazol-3-ium-3-yl)propane1-sulfonate ([Bimps]) zwitterions, to understand the impact of [Bimps] on the enhancement of the electrochemical stability of G4-Li[TFSA] electrolytes at Pt electrode surfaces. The aforementioned interfacial structures were investigated using in-situ infrared-visible sum frequency generation (IV-SFG) spectroscopy. The results of the linear sweep voltammetry (LSV) revealed that the oxidation limit of G4-Li[TFSA] at the Pt electrode shifted to a higher potential when [Bimps] was introduced, thus indicating that the electrochemical window is extended in the G4-Li[TFSA]-[Bimps] system. The SFG spectra of the G4-Li[TFSA] system confirmed that free G4 molecules and Li+-G4 complex cations are dominantly adsorbed on the Pt surface at 1 V (vs. Ag/Ag7). In contrast, the addition of [Bimps] to the G4-Li[TFSA] system resulted in almost full coverage of [Bimps] at the Pt surface by forming Li+-[Bimps] complex cations, even at 1 V (vs. Ag/Ag+), and no free G4 molecules were observed. The ab initio calculation indicated that the highest occupied molecular orbital (HOMO) energy level of free G4 was higher than that of the Li+-[Bimps] complex cation. This suggests that the Li+-[Bimps] complex was more stable for oxidation than the free G4, which accounts for the enhanced electrochemical stability of G4-Li[TFSA] system with [Bimps] additives. (C) 2020 Elsevier Ltd. All rights reserved.