Li-Ion Cell Impedance Measurement Using Open/Short/Load Compensation for De-Embedding

Knowledge of battery cell impedance is crucial for the design of many modern applications, as well as for predicting their electromagnetic compliance. For detailed 3D simulation of battery packs, single cells are commonly replaced with simplified bodies enhanced by internal impedance data obtained from measurement on real cells. Thereby it is necessary to exclude all influence of the measurement setup, i.e. to de-embed the cell impedance from exterior properties. In this work, two approaches are presented to extract the impedance of an 18650 Lithium-ion (Li-ion) cell from within a battery holder on a printed circuit board (PCB), using Open/Short/Load compensation (OSLC) and a copper cylinder as reference. By adding components in series and parallel to the cell, it is verified that the extraction result is not impacted by PCB circuitry, and also that the cell’s impedance is load-independent. Eventually, the test setup including Li-ion cell is replicated as electromagnetic (EM) simulation project. Two measurement-based methods to model the cell are compared, suitable for both 3D or circuit simulation. The frequency range under consideration is from 9 kHz to 1 GHz, whereas the presented approach proves reliable up to 200 MHz.