Reactive Interaction of (Sub-)monolayers and Multilayers of the Ionic Liquid 1-Butyl-1-methylpyrrolidinium Bis(trifluoro-methylsulfonyl)imide with Coadsorbed Lithium on Cu(111)

Abstract

The ionic liquid (IL) 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide [BMP][TFSA] is a promising candidate for improved nextgeneration rechargeable lithium−ion batteries. We here report results of a model study of the reactive interaction of (sub-)monolayers and multilayers of [BMP][TFSA] with lithium (Li) on Cu(111), employing scanning tunnelling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIRS) under ultrahigh vacuum (UHV) conditions. Upon post-deposition of Li on [BMP][TFSA] multilayers at 80 K, we identified changes in the chemical state of the [TFSA] anion and the [BMP] cation as well as in the IR absorption bands related to the anion. These changes are most likely due to the decomposition of the IL adlayer into a variety of products like LiF, Li 2 S, and Li 2 O upon anion decomposition and LiN 3 , LiC x H y N, and Li x CH y upon cation decomposition, where the latter includes cracking of the pyrrolidinium ring. Deposition of Li on [BMP][TFSA] (sub-)monolayer-covered surfaces led to similar decomposition patterns, and the same was also observed for the reverse deposition order. The addition of the corresponding amounts of Li to a [BMP][TFSA] adlayer resulted in distinct changes in the STM images, which must be due to the surface reaction. After annealing to 300 K, the core-level peaks of the cation lose most of their peak area. Upon further heating to 450 K, the anion is nearly completely decomposed, resulting in LiF and Li 2 S decomposition products that dominate the interface.

Electrocatalytic Oxygen Reduction and Oxygen Evolution in Mg‐Free and Mg–Containing Ionic Liquid 1‐Butyl‐1‐Methylpyrrolidinium Bis (Trifluoromethanesulfonyl) Imide

“…In the C 1s range, BMP‐TFSI and Mg‐TFSI 2 lead to peaks related to the CF 3 groups of the TFSI anion (at 292.7 eV) and to two more peaks at 286.6 eV and 285.4 eV, where the latter are assigned to C atoms in the BMP cation, either adjacent to the N atom in the ring (C hetero ) or bonded to other C atoms (C alkyl ), respectively. This assignment corresponds to the findings for a multilayer of BMP‐TFSI on a Cu(111) surface acquired under UHV conditions . The intensity of the peak related to CF 3 groups is generally very small, for the Mn 2 O 3 and MnO 2 electrodes it is even below the signal‐to‐noise ratio.…”

“…For BMP‐TFSI and Mg‐TFSI 2 we used essentially the values reported by Law et al. (see and references therein,), the only deviations are for the CF 3 of TFSI in the C 1s (292.7 instead of 293.1 eV) and F 1s (688.9 instead of 688.7 eV) regions . Table summarizes the BEs of the peaks used in the peak deconvolution.…”

“…This assignment corresponds to the findings for a multilayer of BMP-TFSI on a Cu(111) surface acquired under UHV conditions. [41] The intensity of the peak related to CF 3 groups is generally very small, for the Mn 2 O 3 and MnO 2 electrodes it is even below the signal-to-noise ratio. For the Pt electrode it cannot be fitted with the CF 3 moiety of TFSI alone, since the corresponding amounts of N, S, and O are much lower.…”

“…The binding energies (BEs) of the peaks related to the electrolyte compounds and of the additional peaks were fixed for all electrode materials. For BMP-TFSI and Mg-TFSI 2 we used essentially the values reported by Law et al (see [11] and references therein [41,42] ), the only deviations are for the CF 3 of TFSI in the C 1s (292.7 instead of 293.1 eV) and F 1s (688.9 instead of 688.7 eV) regions. [41] Table 2 summarizes the BEs of the peaks used in the peak deconvolution.…”

Perspective: Chemical reactions in ionic liquids monitored through the gas (vacuum)/liquid interface

“…[67][68][69][70][71][72] We also exclude studies where the reaction was not carried out in situ, that is, spectra were not recorded while the reaction proceeded, or the sample was moved to a different site in the XPS setup or was even removed from the XPS setup in order to carry out the reaction. [73][74][75][76][77] We also do not address studies that incorporate electrochemical sample manipulation, 66,67,[69][70][71][78][79][80][81][82][83][84][85][86] electrodeposition of metal or organic layers from ILs, [87][88][89][90][91] and IL decomposition 84,[92][93][94][95][96][97][98][99][100][101][102] or nanoparticle formation in ILs. 62,75,103 Each of these topics was studied extensively and would justify a separate review.…”