Development of a coupled model of heat generation and jet flow of lithium-ion batteries during thermal runaway

A large amount of heat will be generated during battery thermal runaway. However, the current models for the battery thermal runaway mainly consider the heat generated inside the battery cell and rarely consider the effects of the jet fire. Therefore, it cannot provide an effective way to evaluate the thermal runaway propagation in a battery pack. This study develops a coupled model considering the heat generation inside the battery and the jet fire outside the battery during thermal runaway, which can better evaluate the thermal hazard. Experimental and simulation activities are carried out based on 18,650 cylindrical NCM lithium-ion batteries. First, a test bench is built to trigger and record the thermal runaway. High-speed camera and thermocouples are applied to record the fire shape and temperature. Totally 15 cells with 100 % SOC are abused and six samples experienced intense combustion. The jet fires last for at least 20 s and the maximum combustion temperature was 1075.4 °C, at the location 80 mm above the cell. Then a coupled model consisting of 0D heat generation, gas generation and injection sub-models and 2D CFD sub-model is established based on ANSYS Fluent. The heat and gas generation rates inside the battery are calculated based on chemical reaction mechanisms. The flow, combustion and heat transfer in the open space are solved in a 2D axisymmetric domain. The proposed model can reasonably capture the main characteristic of the jet fire and temperature rise during thermal runaway. The maximum deviation of peak temperature between the experiment and simulation is 8.56 %.