Ionic Liquid Electrolytes Confined Inside Model Nanoporous Carbons: A Molecular Simulation Study

A fundamental understanding of the properties of ionic liquids (ILs) inside nanopores is essential to enhance the performance of energy storage devices such as electrochemical double layer capacitors (EDLCs). Molecular dynamics simulations were performed to study the properties of the IL [emim+][NTf2-], as well as its mixtures with an organic solvent, acetonitrile, when confined inside two model materials, an ideal slit graphitic nanopore and a model nanoporous carbon with roughly rectangular pores that are interconnected. The structure and dynamics of the IL electrolyte vary strongly with pore size, amount of electrolyte inside the nanopores, density of electrical charges in the pore walls, and concentration of IL/acetonitrile. The dynamics of the ions inside the pore are highly heterogeneous, and depend strongly on their position with respect to the pore walls, and on variables such as surface charge density and concentration of IL/acetonitrile. The structural properties of ILs inside nanoporous electrodes affect the macroscopic capacitance in EDLCs, and the dynamical properties of the confined IL is one of the factors that determines the macroscopic electrical resistance in electrochemical devices.