Ionophobic nanopores enhancing the capacitance and charging dynamics in supercapacitors with ionic liquids

Abstract

Nano-porous electrodes combined with ionic liquids (ILs) are widely favored to promote the energy density of supercapacitors. However, this is always accompanied by the reduced power density, especially considering the high viscosity and large steric hindrance of ILs. Here, we use computational simulations coupled with the equivalent circuit model to quantify the charging process and overall performance of the IL-based supercapacitor. We find that the ions in the electrode with ionophobic pores display a new charging mechanism under a threshold potential, namely co-ion adsorption, which has been ignored before. This identified abnormal charging process can not only efficiently enhance the differential capacitance but also remarkably speed up the charging dynamics. Meanwhile, the pores with various sizes and lengths in the electrode demonstrate the same tendency, reflecting the relative universality of the collaborative enhancement of the co-ion adsorption process. Furthermore, the quantitative relation between charging time/capacitance and electric voltage/ionophobic properties is further obtained to evaluate the critical conditions for synergistically improving the energy density and power density of supercapacitors. These findings may advance the understanding of charging mechanisms in porous electrodes and manifest that the ionophobicity is one important factor in the rational design of supercapacitors with ILs or other electrochemical devices in the field of chemical engineering.