Self-Discharge and Voltage Recovery in Graphene Supercapacitors

Graphene supercapacitor, with its higher energy density and power density, is a promising solution for energy storage in many potential applications. The available energy from supercapacitors for stand-alone applications depends on their self-discharge. The effect of charge redistribution on the self-discharge and voltage recovery of graphene supercapacitors is investigated in this work. The self-discharge mechanism in graphene supercapacitors is found to be a combined effect of ohmic leakage and diffusion-controlled leakage due to charge redistribution. The charging process has a predominant effect on the self-discharge. With a higher initial voltage, the supercapacitors exhibit more self-discharge, but with longer charge holding time, the rate of self-discharge is low. The charge redistribution is attributed due to the difference in the accessibility of electrolyte ions to the electrode surface. A phenomenon of voltage recovery is observed in graphene supercapacitors even after complete discharge due to a charge redistribution mechanism. The voltage recovery increases with increasing charge/discharge current.