Structure and Interaction of Ionic Liquid Monolayer on Graphite from First-Principles

The ionic-liquid/graphite interface is important in understanding the behaviors of the ionic-liquid electrolyte in carbon-based supercapacitors and Li-ion batteries. A row-like cation–anion structure of the 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide ([BMP][TFSA]) ionic liquid (a popular choice for interfacial studies) on the graphite surface has been suggested on the basis of scanning tunneling microscopy images, but it is unclear if this structure is the most stable one. Herein, we explore alternative models of the [BMP][TFSA] monolayer on graphite basal plane with first-principles density functional theory. We find that the checkerboard type of structure is in fact more stable than the row-like structure. We further use simulated annealing based on classical molecular dynamics simulations to obtain more stable conformations of ions on the surface. Both charge-density-difference and noncovalent-interaction analyses show that the higher stability of the checkerboard structure than the...