Effects of Polyelectrolyte Surface Coating on the Energy Storage Performance in Supercapacitors

Polymer electrode materials are critical components to achieve the excellent energy storage performance (ESP) of supercapacitors, while the underlying microscopic mechanism by which the polymer structure on the electrode surface affects the energy storage remains unclear. Herein, we explore the effects of a polyelectrolyte (PE) coating on the ESP of supercapacitors by using the polymer density functional theory. The ESP is determined by the adsorption of free ions at the electrode surface, which is jointly affected by the interactions from both the charged surface and the anchored PE chains. Once the PE chains carry like charges as the electrode, the energy density can be significantly promoted by two orders of magnitude. However, if the PE chains carry opposite charges to the electrode, the energy density can be suppressed. The effect of PE coating on the capacitance is similar to that on the energy density if the surface voltage is fixed during the operation, and otherwise, if the surface charge density is fixed, the effect on the capacitance is opposite to that on the energy density. This work provides a microscopic understanding of the complex polyelectrolyte coating's effects on the ESP in supercapacitors.