Experimental and Computational Study on the Interaction of an Ionic Liquid Monolayer with Lithium on Pristine and Lithiated Graphite

Abstract

We report results of a combined experimental and computational model study on the interaction of the battery-relevant ionic liquid (IL) 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([BMP]+[TFSI]−) with Li on pristine highly oriented pyrolytic graphite (HOPG), which aims at a molecular-/atomic-level understanding of the processes at the electrode|electrolyte interface of Li-ion batteries. Employing mainly X-ray and ultraviolet photoelectron spectroscopy as well as dispersion-corrected density functional calculations (DFT-D), we find intact anion–cation pairs for adsorbed [BMP]+[TFSI]− (sub)monolayers on HOPG at 300 K and also on lithiated HOPG at 80 K, that is, under conditions where the mobility of Li+ in the bulk is low. Vapor deposition of [BMP]+[TFSI]− on lithiated HOPG at 300 K results in rapid accumulation of Liδ+ at the surface or in the surface region, indicating that deintercalation is activated under these conditions. This is explained by a dynamic equilibrium between bulk Li+ ...