Abstract
Nanoporous electrodes and room-temperature ionic liquids (RTILs) are promising materials for supercapacitors. The optimization of these materials to achieve high energy density supercapacitors capable of operating at high charging/discharging rates necessitates a fundamental understanding of the dynamic charge storage using these materials. Herein we report atomistic simulations of the cyclic voltammetry of supercapacitors featuring subnanometer pores and RTILs. We show that the cyclic charging and discharging of nanopores are governed by the interplay between the external field-driven ion transport and the sloshing dynamics of ions inside the pore. The ion occupancy and charge distribution along the pore length depend strongly on the scan rate and vary cyclically during the charging/discharging processes. Unlike that at equilibrium conditions or low scan rates, the charge storage at high scan rates is dominated by counterions and co-ions that can even contribute negatively to the charge storage. These observations help explain the perm-selective charge storage observed experimentally. We clarify the mechanisms underlying these dynamic phenomena and quantify their effects on the energy density and efficiency of the dynamic charge storage in nanopores.
