Many different approaches for estimating the parameters of the circuit elements in ECMs can be found in the literature. Thereby, the characterization of the kinetics especially, expressed by the lithium-ion batteries impedance, is of great importance, since a limited set of parameters must cover a broad range of different dynamics in the load profile. The key challenge lies in parameterization of these circuit elements to ensure high accuracy of BMS algorithms. The idea behind ECMs is to model the lithium-ion battery (LIB) with standard circuit elements such as an ideal voltage source modeling the open-circuit behavior, and resistors and capacitors, modeling the kinetics of the LIB. A widespread type of model used for this purpose is the equivalent circuit model (ECM), the complexity of which can easily be adjusted by the number of its circuit elements and the parameterization of which does not require destructive analysis of the cell’s geometry and material properties. To keep the computational effort low to ensure real-time capability and to ensure convergence of estimation algorithms, the complexity of such models and algorithms has to be limited. The parameterized model for a commercial 18650 NCA cell was validated during a validation cycle consisting of constant current and real-world automotive cycling and yields a relative improvement of over 40% compared to a conventional EIS-fitting algorithm. Three different approaches to merge time- and frequency-domain data are presented, including a novel approach where the DRT is simultaneously calculated from electrochemical impedance spectoscropy (EIS) and pulse relaxation measurements. The difficulties of automated deconvolution of the DRT, including regularization and the choice of an optimal regularization factor, is tackled by using the L-curve criterion for optimized calculation of the DRT via Tikhonov regularization. Instead of using only partial information from the DRT to supplement a conventional fitting algorithm, we determine the parameters of an arbitrary number of RC elements directly from the DRT.

This work proposes a method to combine time-domain and frequency-domain measurement data for parameterization of RC elements by exploiting the full potential of the distribution of relaxation times (DRT). However, both types of data have limitations with regard to the observable time constants of electrochemical processes. The RC elements, which display the dynamic loss processes of the cell, are usually parameterized by fitting the ECM to experimental data in either the time-domain or the frequency-domain.

Equivalent circuit models (ECMs) are a widely used modeling approach for lithium-ion batteries in engineering applications.

391 battery pulse current