Impact of different Li-ion cell test conditions on thermal runaway characteristics and gas release measurements

The increasing use of lithium-ion batteries requires further efforts in safety testing and evaluation. It is of utmost importance that the effects of different test conditions are understood, particularly for validation of computer models. While plenty of data from thermal runaway tests are available in literature, few are from large test series. The missing systematic approach to evaluate the impact of different test conditions implies uncertainty when comparing test results. In addition, the fast pace in cell development, including an increasing utilization of larger cells, necessitate the validation of previously published results. This work presents thermal runaway data from 37 tests on one type of large format prismatic lithium-ion cell (157 Ah). The tests are conducted in a closed pressure vessel with inert atmosphere as well as in an open setup below an exhaust collector hood. Further, six different thermal runaway trigger methods are employed as well as four different states of charge. Emphasis is put on the gases produced, a key aspect for safety evaluation. The results are compared with literature data and a new modified method is proposed for calculating the characteristic venting rate in a closed pressure vessel. It is concluded that the trigger method affects the gas production rate, mass loss, and maximum temperature of the cell as much as its state of charge. The large cell format potentially impacts the specific total gas production and enhances the effects of different trigger methods, but has a small impact on other evaluation parameters. No significant differences were observed in the test results due to the different test setups, apart from differences due to potential combustion of the released gases in ambient atmosphere.