Electrothermal Characterization and Modeling of Lithium-Ion Pouch Cells in Thermal Runaway

Electronic applications using lithium-ion batteries are increasingly operated under adverse conditions such as high operating currents and elevated environmental temperatures. Prolonged operation in these adverse conditions induces thermal stresses which can initiate thermal runaway (battery fires). Understanding thermal and performance envelopes for cells is crucial for battery systems’ safe operation. To explore the performance and thermal envelope for safe operation, there is a need for computational tools to predict a cell’s thermal and electrical behavior in any given environment. This paper introduces a model which predicts temperature and voltage profiles of a cell based on operating conditions (current, environmental temperature, etc.). The technique is developed by (1) establishing a 2-resistor-capacitor (2-RC) equivalent circuit model (ECM), (2) parameterizing the ECM in terms of circuit, degradation, and Arrhenius parameters, (3) calibrating parameters through high-pulse-power-characterization (HPPC) and time-constraint insulated-high-pulse-power (TC-IHPP) tests, (4) validating the ECM through discharging tests, and (5) exploring simulated scenarios and examining the ECM’s predictions. Validation results show that with calibrated parameters, the ECM predicts a cell’s electrical and temperature behavior reasonably accurately in a thermal environment and thermal runaway under extreme operating conditions. A degradation model predicts that a cell undergoing thermal runaway loses full capacity before failure initiation. Results show that irreversible and reactive heat are driving factors for a cell’s heating during cycling at low and high temperatures, respectively. Thus, the ECM was simplified by removing additional parameters, which minimized the computational and experimental work required to set up the model. The simplified ECM (SECM) is suitable for scenarios where only average temperature is desired and can predict average temperature and voltage profiles as the original ECM. Finally, a theoretical model is provided to organize effects of electrical activity, thermal runaway kinetics, and environmental temperature on the likelihood for a cell to fail in thermal runaway.