Determination of the Formation Potential of Solid-Electrolyte Interphase in Some Amide-Type Ionic Liquids Containing Metal Salts

Abstract

The formation potentials of the solid-electrolyte interphase (SEI) on a platinum and glassy carbon electrode in two amide-type ionic liquids, 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)amide (BMPFSA) and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA), containing some metal salts were investigated by cyclic voltammetry in the presence of ferrocene (Fc). It is considered that the SEI with the thickness of less than a few nm can be observed by monitoring the shift in the peak potential of Fc+/Fc. The SEIs began to form at ~2.4 V vs. Li|Li(I) in the presence of lithium salts because of a lowering of the lowest unoccupied molecular orbital level of the anion by the interaction with lithium ion. In the case of BMPTFSA containing Ni(TFSA)2, the SEI began to form at –0.7 V vs. Ag|Ag(I), suggesting that the deposition of Ni may be hindered by the SEI formation.