Comparison of accuracy of different LiFePO4 battery circuital models

In recent years lithium iron phosphate batteries are spreading because of their high energy and power density, long lifetime and high inherent safety. In technical literature different models have been proposed to characterize these batteries. These models have different complexity but give results of different accuracy. In this paper a comparison of three equivalent models is performed. The comparison is made taking into account the impedance of the cells as function of the working frequency. For this reason electrochemical impedance spectroscopy method is used. The real and imaginary parts of the impedance calculated at each frequency are compared with that resulting from experimental tests in order to understand which are the frequency limit of each model. From the analysis clearly results that the traditional simple models obtained with 2 or more RC branches cannot represent the behavior of these batteries in all the frequency range. On the contrary, the models presenting a Warburg impedance, even if more complex, can represent the frequency behavior of these batteries in a wider frequency range.