A Comprehensive Numerical Approach to Predict Thermal Runaway in Li-Ion Battery Packs

With the increasing level of electrification of on-road, off-road and stationary applications, use of larger lithium-ion battery packs has become essential. These packs require large capital investments on the order of millions of dollars and pose a significant risk of self-annihilation without rigorous safety evaluation and management. Testing these larger battery packs to validate design changes can be cost prohibitive. A reliable numerical simulation tool to predict battery thermal runaway under various abuse scenarios is essential to engineer safety into the battery pack design stage. A comprehensive testing & simulation workflow has been established to calibrate and validate the numerical modeling approach with the test data for each of the individual sub model - electrochemical, internal short circuit and thermal abuse model. A four-equation thermal abuse model was built and validated for lithium-ion 21700 form factor cylindrical cells using NCA cathodes. The entire coupled model shows a strong agreement with the nail penetration tests, which induces an internal short circuit followed by thermal runaway and fire initiation/propagation, for modules consisting of nine and 72 cells. The developed model is also able to predict the reduced fire propagation behavior in a nine-cell module with a passive thermal management system. The presented numerical approach shows the power of scaling up to perform abuse testing virtually on larger packs after calibrating and validating a smaller module with actual testing.