Investigation of the Ionic Liquid Graphene Electric Double Layer in Supercapacitors Using Constant Potential Simulations

Abstract

In this work, we investigate the effect of the cation structure on the structure and dynamics of the electrode–electrolyte interface using molecular dynamics simulations. A constant potential method is used to capture the behaviour of 1-ethyl-3-methylimidazolium bis (trifluoromethane)sulfonimide ([C2mim][NTf2]) and butyltrimethylammonium bis(trifluoromethane) sulfonimide ([N4,1,1,1][NTf2]) ionic liquids at varying potential differences applied across the supercapacitor. We find that the details of the structure in the electric double layer and the dynamics differ significantly, yet the charge profile and capacitance do not vary greatly. For the systems considered, charging results in the rearrangement and reorientation of ions within ∼1 nm of the electrode rather than the diffusion of ions to/from the bulk region. This occurs on timescales of O(10 ns) for the ionic liquids considered, and depends on the viscosity of the fluid.

Molecular-Level Investigation of Cycloaliphatic Epoxidised Ionic Liquids as a New Generation of Monomers for Versatile Poly(Ionic Liquids)

“…We generated liquid samples by randomly packing the activated monomer and anion [ 38 ] using the PACKMOL software package [ 39 ]. What is meant by “activated monomer” is that the epoxide bond located on both ends of each monomer is broken, and the resulting unsaturated carbon and oxygen atoms are saturated with hydrogen.…”

Structure–Capacitance Relationships of Graphene/Ionic Liquid Electrolyte Double Layers

“…Computational studies have helped to interpret experimental characterization of ionic liquid double layers. ,− A central goal is determining the relationship between the capacitance and the atomistic structure and interactions at the electrode–electrolyte interface. ,− For example, surface roughness , and functionalization , of graphite electrodes have shown pronounced effects on the double-layer structures as well as the enhancement of differential capacitance. Additionally, electrolytes with different chemistry, composition, and concentration have been investigated to illustrate effects on double-layer structure and capacitance, − ,− Other simulations have examined the effect of temperature and/or dispersion forces on the double-layer properties and capacitance profiles. ,, At rough electrode surfaces with pure ionic liquid electrolytes, simulations have shown a significant influence of temperature on the double-layer structure and the capacitance profile . On the other hand, temperature dependence of the capacitance profile is much less significant for less concentrated organic electrolytes at both flat and rough surfaces .…”

EDL structure of ionic liquid-MXene-based supercapacitor and hydrogen bond role on the interface: a molecular dynamics simulation investigation

“…For both IL electrolytes, the σ ave of the Ti 3 C 2 (OH) 2 electrode is more than twice that of the Ti 3 C 2 O 2 electrode as the potential difference increases from 0 to 2 V, and the trend is kept even when the potential difference increases from 2 to 4 V. Therefore, the charging rate of a supercapacitor is closely related to the structures of the electrolytes. 59 At the same time, the charge density is determined by the surficial terminations of the MXene electrodes, and more counterions gather near the –OH terminations, which is beneficial for improving the capacitance. [HEMIm][NTf 2 ] has a faster charging rate, which is in contrast to the intuition when the viscosity is higher than that of [EMIM][NTf 2 ] to reduce the conductivity.…”