Lithium-ion Capacitors: Charge Delivery Capability and Voltage Dependence of Capacitance

This paper examines two characteristics of lithium-ion capacitors (LICs): charge delivery capability during a constant current discharge process and voltage dependence of capacitance. As a hybrid energy storage technology, a LIC is normally composed of a graphite negative electrode typically used in lithium-ion batteries and an activated carbon positive electrode usually included in supercapacitors. To evaluate LICs for potential aerospace applications, this paper first studies the charge delivery capability and investigates the relationship between the delivered charge and the discharge current. Experimental results show that the charge delivery pattern of LICs can be described by Peukert’s law originally developed for lead-acid batteries, which states that the delivered charge is less when the discharge current is higher. Considering the relatively wide operating voltage range of LICs, this paper then studies the dependence of the Peukert constant on voltage. To examine the voltage dependence of the LIC capacitance, this paper adopts the total charge method and the IEC 62391–1 standard method 1A. Experimental results show that the LIC capacitance increases with voltage. For both characteristics, this paper reveals the similarities between LICs and supercapacitors, which suggest that the research methodologies developed for supercapacitors can be applied to LICs.