Effect of thermal impact on the onset and propagation of thermal runaway over cylindrical Li-ion batteries

The external heating test is widely used to evaluate the hazards of battery thermal runaway, but the efficiency and effect of the heating source are rarely quantified. This work performs thermal runaway propagation tests in a 3-layer cylindrical battery pile with a uniform state of charge (SOC) ranging from 30 % to 75 %. A cylindrical heater is in contact with two cells in the first layer and has a power varying from 50 W to 300 W to trigger thermal runaway. Results indicate that for the current system, the heating efficiency to a single cell is around 15 %, and the effective heating power is insensitive to the SOC. The intensity of thermal runaway increases with the external heating power and the cell SOC. The influence of external heating on the propagation of thermal runaway is reflected in the intensity of thermal runaway in the first-layer cells and the preheating effect of subsequent layers. A simplified heat-transfer model is established to quantify the thermal impact on both thermal runaway intensity and preheating depth. Finally, a new approach for selecting the appropriate heating power is proposed to help optimize battery thermal-runaway tests and improve the safety regulations for battery modules.