Molecular-Level Insights into Interfacial Interaction–Nanostructure Relationships of Imidazolium-Based Ionic Liquids around Carbon Nanotube Electrodes

Here, we performed classical molecular dynamics simulations to systematically explore the relationships between interfacial interactions and nanostructures of an imidazolium-based ([BMIM][BF4]) ionic liquid (IL) electrolyte around single-walled carbon nanotube electrodes with various charge densities and nanotube diameters. Our simulation results showed that the aggregation of [BMIM]+ cations around the negative electrodes is dominated by the Coulombic interactions. Meanwhile, it is unexpectedly found that a certain amount of [BMIM]+ cations is distributed near the positive electrode surface, which is attributed to the combined effect of their attractive Coulombic interactions with anions and π–π stacking interactions with nanotubes. Further analysis reveals that the imidazolium rings of cations around the negative (or positive) electrodes with a lower charge density exhibit more ordered orientations compared to the counterparts with a higher charge density. Such phenomena mainly occur because a lower charge density is favorable to form stronger π–π stacking interactions between cations and nanotube electrodes as well as stronger hydrogen bonds within interfacial cations and anions. Hereto, our findings present a crucial step to interpret complicated interactions and nanostructures at the electrolyte–electrode interface, which would benefit experiments in designing high-performance supercapacitors based on carbon electrodes and IL electrolytes.