Dynamics of Charging Subnanometer Pores Using Ionic Liquids

Supercapacitors have advantages such as high power density and extraordinary cyclability, but they provide only moderate energy density. Enhancing supercapacitors’ energy density can enable their widespread deployment. Supercapacitors’ energy density can be increased using ionic liquids and electrodes with subnanometer pores, but this tends to reduce their power density and thus compromising their key advantage. To help address this issue through material optimization, here we unravel the mechanisms of charging subnanometer pores with ionic liquids using molecular dynamics simulations, navigated by a phenomenological model.

We show that charging of ionophilic pores 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. Further acceleration can be achieved using ionophobic pores by eliminating overfilling/de-filling and thus leading to charging behavior qualitatively different from that in conventional, ionophilic pores.