Advanced Fractional-Order Lithium-Ion Capacitor Model With Time-Domain Parameter Identification Method

Lithium-ion capacitor (LIC) is a viable candidate with good commercial prospects in renewable energy, hybrid electric vehicles, and smart grids. It is the convenient route of application development to build the equivalent circuit model of the device in the simulation software. In this article, two advanced fractional-order models of LICs with parameters related to physical properties are proposed to describe the variation of voltage curve in the time domain. The structure of the models is determined based on the reaction process in the frequency domain. The two models differ in their diffusion part in which the fractional differential is introduced into the porous electrode theory in two ways to express the surface inhomogeneity of the porous electrode. The physical significance of the constant phase element (CPE) is particularly analyzed, and it is found that CPE has the ability to describe charge redistribution features. A parameter identification method is presented to solve the parameter estimation difficulties of models with CPE in the time domain. The applicability of the models is verified under constant and dynamic current conditions.