A comprehensive study of supercapacitor Peukert constant dependence on voltage.

This paper presents a comprehensive study of the supercapacitor Peukert constant dependence on its terminal voltage. Recent studies show that the charge delivered by a supercapacitor during a constant current discharge process increases when the discharge current decreases if the discharge current is above a certain threshold, i.e., Peukert's law applies. This paper investigates the supercapacitor Peukert constant dependence on the initial voltage, cutoff voltage, and voltage difference of the constant current discharge process. Experimental results show that the Peukert constant is lower when the cutoff voltage is lower (the initial voltage is fixed) or the initial voltage is higher (the cutoff voltage or voltage difference is fixed). The physical mechanisms accounting for these observations are analyzed. When the voltage difference is larger (the initial voltage or cutoff voltage is fixed), more charge is released. For the same voltage difference, more charge is delivered when the initial voltage is higher due to the voltage dependence of the supercapacitor capacitance. In these scenarios, the discharge time is longer, the branch capacitors are more deeply discharged and their depths of discharge are higher, which makes them more responsive to the discharge current and ultimately leads to a smaller Peukert constant.