Measurement and equivalent circuit modeling of a lithium-ion cell

Impedance spectroscopy, charge/discharge curves and pulsed current measurements are used to identify cell response as a function of voltage and frequency, and in turn to create a non-linear time domain circuit model of a cell. The cell studied incorporates a lithium nickel manganese cobalt electrode. Linear finite transmission line models are fitted to the frequency response to identify model parameters, including equivalent series resistance, charge transfer resistance, double layer capacitance and mass transfer resistance. The frequency response is obtained at a number of states of charge so that the dependence of these properties on state of charge can be estimated. Constant current charging is used to estimate effective capacitance as a function of state of charge. A non-linear capacitor in series with an equivalent circuit resistance effectively predicts cell time response to pulsed current inputs, except where gradients in local state of charge exist within electrodes.