Solid-Electrolyte Interphase Formation in Amide-Type Ionic Liquids in the Presence of Different Metal Cations

Abstract

The formation of solid-electrolyte interphase (SEI) on a glassy carbon (GC) electrode in 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)amide (BMPFSA) and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA) containing Li+, Na+, K+, and Ni2+ was investigated using the redox reaction of ferrocene (Fc). The anodic peak potential (E pa) for the oxidation of Fc changed after holding the electrode at –1.4 to –1.5 V vs Ag|Ag(I) in BMPFSA in the presence of the alkali metal ions. The decomposition of FSA– was confirmed by X-ray photoelectron spectroscopy (XPS) on a GC electrode held at –1.5 V vs Ag|Ag(I) for 6 h in BMPFSA containing the alkali metal ions. The change in E pa may also suggest the formation of homogeneous SEI in the FSA–-type ionic liquid. Moreover, E pa changed after holding the electrode at the potential more negative than –0.9 V vs Ag|Ag(I) in 50 mM Ni(TFSA)2/BMPTFSA while the decomposition of TFSA– was not confirmed by XPS on the electrode held at –1.1 V vs Ag|Ag(I) for 6 h, suggesting the bonds except C-F (e.g., S-C) were dissociated to form the SEI. Since the deposition potential of Ni in BMPTFSA was more negative than the SEI formation potential, the deposition of Ni may be inhibited by the SEI.