Li-ion battery modeling optimization based on Electrical Impedance Spectroscopy measurements

Li-ion batteries are a very attractive energy storage technology due to their high energy density and their capability for high charge and discharge rates. This makes them very suitable for power applications such as Electric Vehicles (EV), Hybrid Electric Vehicles (HEV) or electric grid oriented applications. However, in order to take advantage of Li-ion batteries´ good properties, an accurate battery model is needed, as it provides a tool to know how the cell will behave without doing time consuming tests. Although many battery models can already be found in the literature, the need to compare different models´ accuracy appears. This paper presents an analysis and testing of second and third order electrical equivalent models for a 6.5Ah, LiFePO₄ cell type, whose parameters are obtained from an Electrochemical Impedance Spectroscopy (EIS) and a subsequent model fitting process. In addition, an optimization criterion is presented for the fitting process, which improves the accuracy of the models and reduces the parameter estimation time from 61h to 6h for the presented models.