Thermal Runaway Propagation – Critical Variables and Protocols

This study describes the efforts taken to determine the variables that are critical to obtain consistent and repeatable results to initiate thermal runaway in Li-ion multi-cell packages and modules. In this study, lithium primary cells were also studied under similar conditions. A series of tests were conducted to evaluate the effects of various parameters which need to be considered when designing experimental studies to investigate the thermal runaway behaviors of Li-ion batteries. The results show that a heating rate of 5 to 10 °C/min produced the most stable and consistent results than higher or lower heating rates but 10 °C/min was chosen as the standard for a majority of the tests. The control thermocouple positioned 5 mm from a heater provided more accurate measurements of the heating rate of the cell avoiding excessively high temperatures near the heater. The comparison between two heating methods, a heater and oven, showed that the heater offered better control of the heating rate but can be the cause of other unexpected reactions due to venting of semi-solids from the cell if the temperatures exceeded a certain limit, whereas the oven heating provided uniform heating across the cell surface by convective heating. The states of charge (SOC) greatly affected the propagation of thermal runaway between Li-ion cells. The results highlight the importance of test configuration and settings which may impact the outcome of the tests.