Impacts of experimental setup and cell vent opening on large cylindrical cell thermal runaway performance

• The completeness of the cell vent opening significantly impacts the TR result. • The gas mixture primarily consists of 40% CO2, 36–38% CO, 14–15% H2 and 3–7% CH4. • The gas volume ranges between 23 and 27 L. • The method for securing voltage sense leads has to withstand the TR temperature. Thermal runaway (TR) performance of 18,650 and 21,700 cylindrical cells under different State of Charge (SOC), State of Health (SOH), and/or ambient pressure has been systematically studied and reported in the literature. However, the experimental setup and TR performance of large cylindrical cells like 4680 have not been thoroughly explored. This study investigates the impact of three different cell voltage measurement methods and the effects of complete and incomplete cell vent openings on 4680 cylindrical cells subjected to convection-induced TR test. The analysis demonstrated three key findings. First, the completeness of the cell vent opening significantly influences the internal mass distribution, measured gas temperature and surface temperature. With incomplete cell vent opening, the jelly roll was pushed towards the cell vent, resulting in more remaining aluminum disk, a lower measured maximum gas temperature, and a higher surface temperature on the cell bottom plate. In contrast, with a completely opened cell vent, the jelly roll was torn apart from the middle, leading to increased consumption of aluminum disk and a slightly reduced mass loss. Additionally, all three tests exhibited two-stage venting events, with the first (pre-TR venting) not dropping the voltage to 0 V, while the second (TR venting) did. Second, the gas compositions were found to be 40 % CO 2 , 36–38 % CO, 14–15 % H 2 and 3–7 % CH 4 , with a captured gas volume between 23 and 27 L. Finally, the method for securing cell voltage sense leads to the cell terminals has to withstand the TR initiation temperatures to maintain clear and uninterrupted voltage reading. Understanding the TR behavior of cells, along with gas volume and compositions is crucial for developing effective countermeasures.