  Molecular dynamics simulations have been used extensively to determine
equilibrium properties of the electrode-electrolyte interface in
supercapacitors held at various potentials. While such studies are essential to
understand and optimize the performance of such energy storage systems,
investigations of the dynamics of adsorption during the charge of the
supercapacitors is also necessary. Dynamical properties are especially
important to get an insight into the power density of supercapacitors, one of
their main assets. In this work, we propose a new method to analyze the
trajectories of adsorbing ions. We focus on pure 1-ethyl-3-methylimidazolium
bis(trifluoromethylsulfonyl)imide in contact with planar carbon electrodes. We
characterize the evolution of the ion orientation and ion-electrode distance
during adsorption and show that ions reorientate as they adsorb. We then
determine the forces experienced by the adsorbing ions and demonstrate that
Coulomb forces dominate at long range while van der Waals forces dominate at
short range. We also show that there is an almost equal contribution from the
two forces at an intermediate distance, explaining the peak of ion density
close to the electrode surface.
