Effects of Supercapacitor Physics on Its Charge Capacity.

Abstract

This paper investigates the effects of three aspects of the supercapacitor physics on its charge capacity: porous electrode structure, charge redistribution, and self-discharge. The relationship between the delivered charge and the discharge current is examined for both the upper and lower bounds of the utilized charge capacity, which refers to the amount of charge delivered during a constant current discharge process. In the upper bound case, Peukert's law applies when the discharge current is above a certain threshold and does not apply anymore if the discharge current is below the threshold. In the lower bound case, if the discharge current is above the threshold, the delivered charge increases when the discharge current decreases although the increase rate is lower compared to that in the upper bound case. The individual and combined effects of supercapacitor physics are studied. The porous electrode structure and the charge redistribution process result in an increase in the delivered charge when a smaller discharge current is applied. The impact of self-discharge is negligible when the discharge current is relatively large. If the discharge current is sufficiently small, self-discharge results in a significant energy loss and consequently a drop in the delivered charge.