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

In this study, we propose a “checkerboard” adsorption model for Ionic liquids (ILs) on lithium metal electrode surfaces. We selected several classical ILs featuring pyrrolidinium cations with alkyl chains of varying lengths (Cxmpyr, x = 1, 2, 3, 4, 5, 6) and two anions: bis(trifluoromethylsulfonyl)imide (TFSI–) and fluorosulfonylimide (FSI–). By varying the ILs combinations, as well as the orientations and cis–trans isomerism of the anions, we constructed 72 adsorption models. These models were optimized using density functional theory with dispersion correction (DFT-D3). The optimized structures underwent extensive analysis, including electrostatic potential mapping, topological analysis via atoms in molecules theory, independent gradient model analysis, and electron density difference assessment. Comparisons were made with our previous adsorption models on graphite surfaces, revealing significant differences between the graphite and lithium metal surfaces. Finally, through ab initio molecular dynamics simulations, we compared the stability of the checkerboard configuration with the conventional row-like configuration, demonstrating the superior stability of the checkerboard-like configuration as a self-assembled structure.