Study on Thermal Runaway Propagation Characteristics and Cooling Inhibition Mechanism of Lithium-Ion Batteries

New energy vehicles have been recognized and promoted worldwide, but the safety hazards caused by thermal runaway and misfire of power lithium-ion batteries are still major challenges. This paper presents a three-dimensional thermal runaway simulation model that accounts for inter-cell coupling, chemical reactions, and heat transfer within a battery pack. The model investigates the propagation of thermal runaway, the heat diffusion process, and the suppression mechanisms under varying SOC conditions. By examining the refrigerant role in mitigating thermal runaway, it identifies the critical conditions necessary for effective thermal suppression of batteries using liquid CO2 and R410A as refrigerant at the early stage of thermal runaway. The results firstly show that the critical temperature rise for NCM and LFP batteries was observed within the ranges of 80-90 K and 105-120 K, respectively. Additionally, the critical propagation times were found to be in the ranges of 95-120 s and approximately 3000 s. The study also finds that the refrigerant can effectively lower the temperature of the power battery pack, thereby delaying the propagation of thermal runaway and enhancing safety. The critical times for NCM and LFP batteries are 75 and 150 s, respectively, while the essential flow rates required for effective suppression of thermal runaway are 0.080 kg/s for NCM and 0.038 kg/s for LFP. Notably, the thermal runaway of NCM batteries can be significantly mitigated with an application of refrigerant lasting 200 s; conversely, the critical emergency time for LFP battery thermal runaway is reduced to 150 s. Thus, the corresponding emergency critical times for NCM and LFP batteries are established as 75 and 150 s, respectively. It offers data support for the safe operation and emergency backup of large battery systems.