title: Interaction of a Self-Assembled Ionic Liquid Layer with Graphite(0001): A Combined Experimental and Theoretical Study.
abstract: The interaction between (sub)monolayers of the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide [BMP](+)[TFSA](-) and graphite(0001), which serves as a model for the anode|electolyte interface in Li-ion batteries, was investigated under ultrahigh vacuum conditions in a combined experimental and theoretical approach. High-resolution scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and dispersion-corrected density functional theory (DFT-D) calculations were employed. After vapor deposition at 300 K, XPS indicates molecular adsorbates with a 1:1 ratio of cations/anions. Cool down to ∼100 K leads to the formation of an ordered (2D) crystalline phase, which coexists with a mobile (2D) liquid. DFT-D calculations reveal that adsorbed [BMP](+) and [TFSA](-) species are arranged alternately in a row-like adsorption structure (cation-anion-cation-anion) and that adsorption is dominated by dispersion interactions between adlayer and substrate, on the one hand, and electrostatic interactions between the ions in a row, on the other hand. Simulated STM images of that structure closely resemble the experimental molecular resolved STM images and show that the resolved features mostly stem from the cations.
authors.affiliation: Helmholtz-Institute-Ulm (HIU) , Electrochemical Energy Storage, Helmholtzstraße 11, D-89081 Ulm, Germany.
authors.forename: Florian
authors.initials: F
authors.lastname: Buchner
authors.affiliation: Helmholtz-Institute-Ulm (HIU) , Electrochemical Energy Storage, Helmholtzstraße 11, D-89081 Ulm, Germany.
authors.forename: Katrin
authors.initials: K
authors.lastname: Forster-Tonigold
authors.affiliation: Ulm University , Institute of Surface Chemistry and Catalysis, Albert-Einstein-Allee 47, D-89081 Ulm, Germany.
authors.forename: Maral
authors.initials: M
authors.lastname: Bozorgchenani
authors.affiliation: Helmholtz-Institute-Ulm (HIU) , Electrochemical Energy Storage, Helmholtzstraße 11, D-89081 Ulm, Germany.|Ulm University , Institute of Theoretical Chemistry, Albert-Einstein-Allee 11, D-89081 Ulm, Germany.
authors.forename: Axel
authors.initials: A
authors.lastname: Gross
authors.affiliation: Helmholtz-Institute-Ulm (HIU) , Electrochemical Energy Storage, Helmholtzstraße 11, D-89081 Ulm, Germany.|Ulm University , Institute of Surface Chemistry and Catalysis, Albert-Einstein-Allee 47, D-89081 Ulm, Germany.
authors.forename: R Jürgen
authors.initials: RJ
authors.lastname: Behm