A Physical-Based High-Frequency Model of Cylindrical Lithium-Ion Batteries for Time Domain Simulation

Lithium-ion (Li-ion) batteries in electric vehicles are exposed to high slew rate currents originating from the power electronics. Modern gallium nitride and silicon carbide-based power converters generate high switching frequencies, which propagate toward the battery. To predict the battery's impact on conducted emissions, we need to determine the battery's behavior over a high-frequency bandwidth. Traditional battery characterization techniques such as electrochemical impedance spectroscopy focus on frequencies below 10 kHz. This article proposes a novel method to characterize the battery beyond typical EIS frequencies. Developing a novel fixture to mount a single battery and applying proper de-embedding techniques enable a cell characterization from 1 kHz up to frequencies as high as 300 MHz using the 2-port shunt-through vector network analyzer (VNA) method. The cell's HF impedance originates from several loss processes such as skin effect, ionic shunt effect, and simple ohmic-inductive effects. First in literature, all these effects are measured and summarized in an equivalent electrical circuit model, which predicts the cell's impact on HF current pulses.