Effect of mechanical extrusion force on thermal runaway of lithium-ion batteries caused by flat heating

The thermal runaway (TR) of lithium-ion batteries (LIBs) hinders the development of new energy vehicles (NEVs) because its extrusion-state characteristics remain unclear. Here, 100% state of charge (SOC) pouch LIBs are heated under extrusion, for triggering TR. The battery temperature, voltage, and deformation during the TR are recorded, and a high-speed infrared camera is used along with a high-definition camera for capturing the TR's flame evolution process. The battery thickness gradually decreases with increasing the temperature of a squeezed-state battery, until dropping abruptly at the TR onset. In the squeezed state, smoke is produced for a shorter time, the TR jet intensity significantly increases, and the wreckage exhibits a tight block structure. The TR onset occurs faster for higher squeezing pressures, the jet fire duration is shorter, while the flame temperature and area increase. The maximal temperature of the battery surface increases first and then drops, and the mechanism of the TR gradually changes from heating to internal circuit shorting. For squeezing pressures under 5000 N, the TR onset temperature increases slightly compare with the non-squeezed state, and then decreases to approximately 100 degrees C as the pressure approaches 5000 N.