Abstract
We report detailed simulation results on the formation dynamics of an electrical double
layer (EDL) inside an electrochemical cell featuring room-temperature ionic liquids (RTILs)
enclosed between two planar electrodes. Under relatively small charging currents, the evolution
of cell potential during charging can be suitably predicted by the Landau-Ginzburg-type
continuum model proposed recently (M. Z. Bazant, B. D. Storey, and A. A. Kornyshev, Phys.
Rev. Lett., 106, 046102, 2011). Under very large charging currents, the cell potential shows
pronounced oscillation during the initial stage of charging, a feature not captured by the
continuum model. Such oscillation originates from the sequential growth of the ionic space
charge layers near the electrode surface, allowing the evolution of EDLs in RTILs with time, an
atomistic process difficult to visualize experimentally, to be studied by analyzing the cell
potential under constant current charging conditions. While the continuum model cannot predict
the potential oscillation under such far-from-equilibrium charging conditions, it can nevertheless
qualitatively capture the growth of cell potential during the later stage of charging. Improving the
continuum model by introducing frequency-dependent dielectric constant and density-dependent
ion diffusion coefficients may help to further extend the applicability of the model.
Keywords: ionic
