Release characteristics of escaping gases from lithium-ion battery cells of electric vehicles in short-stack and module configuration

With the ongoing transition to electromobility, lithium-ion batteries (LIBs) play an important role in supporting the decarbonization of road transport (passenger cars, light commercial vehicles, heavy commercial vehicles). However, with the rapid technological development of LIBs and their increasing use, safety-related problems of electric vehicles caused by battery thermal runaway have been widely reported. Thermal runaway (TR) can be accompanied by the release of toxic gases, fire, flames and explosions, posing a serious danger to people in the vicinity (passengers, first responders, firefighters, bystanders) and buildings (confined spaces such as parking garages, garages, houses).

Therefore, it is critical to understand the behavior of lithium-ion battery cells under test conditions that reflect the various conditions an EV battery system is exposed to during operation. In this thermal runaway and propagation study, large size pouch cells (40 Ah) taken from a commercial electric vehicle were arranged in different configurations: 2-cell short stack, 5-cell short stack, 10s2 module. Two methods of triggering thermal runaway, nail drilling and rapid heating, were used and the influence of inter-cell insulation materials was evaluated. The tests were performed in an open setup within a test room of 100 m³. A gas sampling probe was placed laterally, above the test object (DUT), to monitor, characterize and quantify the released gases using online Fourier transform infrared spectroscopy (FTIR).

The gases collected during a test were further analyzed using a gas chromatography-mass spectrometry (GC-MS) system. The focus of this work is on the gaseous products and the behavior of gas evolution / dynamics as a function of time during the TR and TP experiment. We will present the dynamics of gas release and a toxicity assessment of these gaseous products using, where possible, the Acute Exposure Guideline Levels-2 (AEGL-2).