Ionic liquids intercalation in titanium carbide MXenes: A first-principles investigation

Abstract

Herein, we present a density functional theory with dispersion correction (DFT-D) calculations that focus on the intercalation of ionic liquids (ILs) electrolytes into the two-dimensional (2D) Ti₃C₂T_x MXenes. These ILs include the cation 1-ethyl-3-methylimidazolium (Emim⁺), accompanied by three distinct anions: bis(trifluoromethylsulfonyl)imide (TFSA⁻), (fluorosulfonyl)imide (FSA⁻) and fluorosulfonyl(trifluoromethanesulfonyl)imide (FTFSA⁻). By altering the surface termination elements, we explore the intricate geometries of IL intercalation in neutral, negative, and positive pore systems. Accurate estimation of charge transfer is achieved through five population analysis models, such as Hirshfeld, Hirshfeld-I, DDEC6 (density derived electrostatic and chemical), Bader, and VDD (voronoi deformation density) charges. In this work, we recommend the DDEC6 and Hirshfeld-I charge models, as they offer moderate values and exhibit reasonable trends. The investigation, aimed at visualizing non-covalent interactions, elucidates the role of cation-MXene and anion-MXene interactions in governing the intercalation phenomenon of ionic liquids within MXenes. The magnitude of this role depends on two factors: the specific arrangement of the cation, and the nature of the anionic species involved in the process.