Surface Science and Electrochemical Model Studies on the Interaction of Graphite and Li‐Containing Ionic Liquids

The process of solid–electrolyte interphase (SEI) formation is systematically investigated along with its chemical composition on carbon electrodes in an ionic liquid‐based, Li‐containing electrolyte in a combined surface science and electrochemical model study using highly oriented pyrolytic graphite (HOPG) and binder‐free graphite powder electrodes (Mage) as model systems. The chemical decomposition process is explored by deposition of Li on a pre‐deposited multilayer film of 1‐butyl‐1‐methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([BMP][TFSI]) under ultrahigh vacuum conditions. Electrochemical SEI formation is induced by and monitored during potential cycling in [BMP][TFSI]+0.1 m LiTFSI. The chemical composition of the resulting layers is characterized by X‐ray photoelectron spectroscopy (XPS), both at the surface and in deeper layers, closer to the electrode|SEI interface, after partial removal of the film by Ar+ ion sputtering. Clear differences between chemical and electrochemical SEI formation, and also between SEI formation on HOPG and Mage electrodes, are observed and discussed. Interphase formation during Li post‐deposition on multilayers of the ionic liquid (IL) 1‐butyl‐1‐methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([BMP][TFSI]) on highly oriented pyrolytic graphite is studied under vacuum and during electrochemical cycling of graphite electrodes in Li+‐containing [BMP][TFSI] by using X‐ray photoelectron spectroscopy. [BMP]+ decomposition occurs preferentially during Li0‐induced IL decomposition, whereas electrochemical cycling leads to [TFSI]− reduction.