Fractional Thermal Runaway Calorimetry: A Novel Tool to Assess Battery Thermal Runaway Energy

The use of Lithium-ion batteries in the transportation sector has its own unique set of requirements such as high-power demands, cooling challenges, and risk of mechanical failure due to crashes. Active and passive components of thermal management systems in battery-powered products are designed to mitigate the effects of thermal runaway events and prevent cell-to-cell propagation. Designing safe battery-powered systems requires an understanding of how the battery pack will behave while undergoing thermal runaway, including critical data such as total energy yielded, rate of energy generation, as well as venting patterns and directions. Details such as thermal runaway energy fractions associated with the cell casing as well as vent gas and ejecta can be used to inform and optimize battery pack designs and the product as a whole. The NASA Fractional Thermal Runaway Calorimeter (FTRC) was created to measure these values. In this work, the FTRC technology is reviewed along with examples of experimental data sets collected using this methodology. Two sets of FTRC tests are presented. In the first set of FTRC results, tests of three 18650 battery cells charged to 100% state of charge (SOC) are conducted using nail penetration failure. The second set of FTRC results are from thermal runaway tests of four 18650 battery cells initiated by external heating failure, each charged to a different SOC, ranging from 25%-100%.