The interaction of several fluorinated ionic liquids on the LiF(001) surface

LiF is a well-known constituent of the solid electrolyte interphase (SEI) layer in lithium metal batteries, which spontaneously forms in the presence of electrolytes and additives. The subsequent interaction of the electrolyte with this component at the atomic scale, however, is largely unreported. In this work, density functional theory (DFT) calculations were used to examine the interaction of several ILs, specifically 1-methyl-1-propylpyrrolidinium cation (Pyr(13)(+)) paired with the fluorinated anions bis(fluorosulfonyl)imide (FSI-), fluorosulfonyl-(trifluoromethanesulfonyl)imide (FTFSI-), and bis(trifluoromethylsulfonyl)imide (TFSI-) on a LiF(001) surface, to detail their adsorption characteristics. Each IL was shown to adsorb onto the LiF surface in different orientations via the anion O and F atoms and the cation H atoms, with binding energies ranging from-1.54 to-0.22 eV. These surface binding energies are significantly weaker than the corresponding anion-cation interaction energy. The thermal stability of each IL on the LiF surface was explored via AIMD simulations at 428 K, revealing that each of the examined IL pairs did not dissociate on the surface within the examined simulation time. This work further reinforces the stability of fluorinated ionic liquids on a LiF interface and provides a highly detailed account of the adsorption process.