Analysis of Thermal Runaway in Pouch-Type Lithium-Ion Batteries Using Particle Image Velocimetry

Despite widespread recognition of the serious risk of battery thermal runaway (BTR) in lithium-ion batteries, the process and associated external ignition mechanism remain poorly understood. In this study, BTR was measured using thermodynamics and visualization techniques in 10 lithium-ion batteries under thermal abuse conditions. The venting speed was measured by particle image velocimetry and boundary detection. The external ignition mechanism was characterized in terms of flame area. The average BTR onset temperature across the 10 test batteries was 215.6 degrees C. The average maximum temperature was 831.1 degrees C, and the variation between experiments was high compared with the BTR onset temperature due to swelling, repairing, and venting. BTR occurred in four stages (ejection of vent gas with flame, extinction of flame, random and simultaneous ignition, and flame propagation and flame jet formation). The initial average venting speed was approximately 123.8 m/s. The structural and venting speeds of vent gas were similar after a stable flame jet formed. The speed of the core of the gas jet peaked at 20 to 40 m/s. The venting speed decreased as the distance from the jet core increased.