Development of a First Principles Equivalent Circuit Model for a Lithium Ion Battery

This paper examines the development of a linear single particle model that can be used for model based power train simulation, design, estimation and control in hybrid and electric vehicles. The model assumes that the cell consists of spherical particles in each electrode, neglects the electrolyte dynamics, and uses Padé approximations of the particle transcendental transfer functions. The Padé approximated single particle model matches well with the transcendental model, indicating the accuracy of 3rd order Padé approximations for the particle surface concentrations. This model also accurately reproduces the frequency response of a more complex model from the literature, showing that electrolyte diffusion has limited impact on cell impedance. The model also predicts the experimentally measured EIS and moderate (≤ 5C) current pulse charge/discharge of a 3.1 Ah Li-ion cell. The explicit form of the impedance allows the development of an equivalent circuit with resistances and capacitances related to the cell parameters.