Understanding the dynamic charge storage in nanoporous electrodes with room-temperature ionic liquids is essential for optimizing them to achieve supercapacitors with high energy and power densities. In this presentation, we will introduce our recent work on this topic. First, we simulated the charging of sub-nanometer pores driven by an impulsively imposed voltage. We show that charging observes an effective diffusion law. Charging is often accompanied by overfilling followed by de-filling. In sharp contrast to conventional expectations, charging is fast because ion diffusion during charging can be an order of magnitude faster than in the bulk, and charging itself is accelerated by collective modes. Next, we studied the cyclic voltammetry of supercapacitors featuring subnanometer pores and model ionic liquids. 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 along the pore length depends strongly on the scan rate and varies cyclically during charging/discharging. Unlike that at equilibrium conditions or low scan rates, charge storage at high scan rates is dominated by counterions while the contribution by co-ions is marginal or negative. 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 efficiency of the dynamic charge storage in nanopores.

Dynamic charge storage in nanopores filled with ionic liquids

251st National Meeting (2016)

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