Evaluation of detection criteria for thermal runaway experiments on commercial cells for electric vehicles

Abstract

With electric vehicles being more and more present on the roads, the possibility of battery fires attracts much attention. Such fires can start as thermal runaway events in a single cell and propagate to neighboring cells.Early detection of thermal runaways is crucial for passenger egress from the vehicle in case of fire. For Regulatory tests, international standards and regulations are available providing criteria based on cell voltage or temperature combined with the temperature rate dT/dt for the detection of thermal runway events. All documents use combinations of several criteria for the identification of thermal runaway events. However, there are differences in the definitions and combinations of these criteria. Based on international guidance documents, we specify thermal runaway detection criteria and apply these to data from thermal runaway tests on commercial single cells for electric vehicles. The runaway events were triggered by nail penetration or by heater on various cell formats.We compare the accuracy of combined criteria and thresholds with regard to their ability for distinguishing between thermal events that led to thermal runaway and those that did not.For our tests, the criteria based on cell temperature and its rate are more reliable than the combination of temperature rate and cell voltage.

Keywords

• Lithium ion cell
• Thermal runaway criterion
• Standards