Influence of Open Circuit Voltage Measurement on Battery Voltage Modeling

Accurate State of Charge (SOC) - Open Circuit Voltage (OCV) relationship plays a significant role in battery modeling. This paper compares two methods to obtain the SOCOCV relationship: low-rate constant current (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{C} / 20$</tex> ) testing and Galvanostatic Intermittent Titration Technique (GITT). While GITT tests typically use rest periods of 1-2 hours, the optimal duration remains unclear, especially at low SOC levels and lower temperatures. This research investigates the optimal rest period required for GITT tests at 25° C and 40° C by analyzing voltage relaxation rates <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$d V / d t$</tex> at various intervals after the current pulse. Experiments were conducted with relaxation periods ranging from 5 minutes to 4 hours across the full SOC range. The resulting SOC-OCV relationships were then used with parameters obtained from Hybrid Pulse Power Characterization (HPPC) test data to develop second-order Thevenin equivalent circuit model (ECM). Model performance was evaluated using constant current profiles and dynamic drive cycles, demonstrating the impact of different methods of OCV measurement on the accuracy of the prediction. Results indicate that SOC-dependent relaxation periods optimize the balance between test duration and measurement accuracy.