Monochromatic X-ray Photoelectron Spectroscopy Study of Three Different Ionic Liquids in Interaction with Lithium-Decorated Copper Surfaces

Abstract

A comparative study of the chemical reactions of three different ionic liquids prepared by physical vapor deposition on a Li/Cu surface was performed. In this investigation, the ionic liquids 1-butyl-1-methylpyrrolidinium bis­[fluorosulfonyl]­imide ([Py1,4]­FSI), 1-butyl-1-methylpyrrolidinium bis­[trifluoromethylsulfonyl]­imide ([Py1,4]­TFSI), and 1-octyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­imide ([OMIm]­TFSI) were characterized by monochromatic X-ray photoelectron spectroscopy after adsorption on Li/Cu. All spectra prove the formation of LiF and Li2O, which verifies the partial decomposition of the anions. This is found to be much less intense for [Py1,4]­TFSI than for [Py1,4]­FSI, indicating a more rapid decomposition of the FSI anion in the presence of lithium. In addition, changes of the cation structure, as well as changes of the anion/cation ratio, were observed in the spectra. In summary, cations were most likely displaced from the Li/Cu surface and were partially decomposed, especially in case of [OMIm]­TFSI, due to the interaction with lithium. The results give an overview on the possible reaction products at the Li surface when using ionic liquids as electrolytes or additives for lithium batteries. Additionally, it gives an insight into the specific role of the cations and anions for the formation of the solid electrolyte interphase layer in battery systems.

Structure formation and surface chemistry of ionic liquids on model electrode surfaces—Model studies for the electrode | electrolyte interface in Li-ion batteries

“…In the present article, we put our previous results on the structure formation and surface chemistry of adsorbed IL (sub-)monolayers into a common perspective. We will concentrate on adsorption and reaction studies using the battery-relevant IL butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [ 27 [BMP] + [TFSA] -, 32,33 [Py 1,4 ]TFSA, 34 [Py 1,4 ]TFSI 35 and [C 4 C 1 Pyrr] + [Tf 2 N] - 36,37 have been used for this compound previously.…”

“…[TFSI] --based ILs with different cations with single crystalline surfaces has been investigated (ex situ) under UHV conditions [35][36][37][38][39][40][41][42][43][44][45][46][47][48][49] and in-situ in an electrochemical environment. [32][33][34][50][51][52][53][54][55] For example, employing angle-resolved X-ray photoelectron spectroscopy (ARXPS), Cremer ("checkerboard") arrangement on Au(111), with both anions and cations bound directly to the surface.…”

“…The new peaks are related to the decomposition of predominantly [TFSI]anions into products such as Li 3 N, LiF, Li 2 S, Li x SO x , Li 2 O, LiOH, etc. 35,36,84. Interestingly, in the presence of a preadsorbed [BMP] + [TFSI] -(sub-)monolayer, almost all postdepostited Li remains in the surface region, as indicated by the emergence of a peak with significant intensity in the Li 1s range at ~ 56.5 eV (yellow), which is assigned to Li-containing decomposition products (metallic Li is expected at a lower BE of ~ 55.4 eV24,27 ).…”

X-ray Photoelectron Spectroscopy with Electrical Modulation Can Be Used to Probe Electrical Properties of Liquids and Their Interfaces at Different Stages

“…21−27 Our initial work in this area started with the investigation of ionic liquids as the electrolyte medium of a coplanar capacitor and using the binding energy shifts of the F 1s core level representing the anion of the ionic liquid, following polarization of one of the metal electrodes by the application of external dc and/or ac electrical bias. 28 That investigation enabled us to follow the electrical potential developments between the metal electrodes in both laterally and temporally resolved fashions. We then extended the investigation to probing the nature of an electrochemical corrosion process between the ionic liquid and Au electrodes 29 and finally to detecting, in situ, electrochemically generated carbene formation 30 and its CS 2 adduct.…”

Lithium-ion battery performance enhanced by the combination of Si thin flake anodes and binary ionic liquid systems

“…[26][27][28] In the IL electrolytes used in the present study, the SEI layer is believed to be generated by the decomposition of FSA and TFSA anions. 14,16,[29][30][31][32][33] Fig. 5 1 eV), which is known as one of the SEI components having high Li-ion conductivity.…”