Equivalent circuit models and parameter identification methods for lithium-ion capacitors

As a new type of energy storage devices with both high energy density and power density, lithium-ion capacitors have exhibited applicable prospects in the field of renewable energy and transportation. In order to explore possible applications of lithium-ion capacitors, equivalent circuit models have been extensively studied. The models are capable of representing the terminal characteristics of a cell. This paper establishes and compares two equivalent circuit models for lithium-ion capacitors: a classical model and a two-branch model. The experimental and simulation results of the two equivalent circuit models are compared under various working conditions to validate the accuracy of the models. A new parameter identification method combining numerical fitting and circuit analytical is developed for the two-branch model. Moreover, the assumptions and preconditions of the two-branch model are deeply analyzed to obtain a general parameter identification method.