Experimental and analytical investigation on the thermal runaway propagation characteristics of lithium-ion battery module with NCM pouch cells under various state of charge and spacing

Thermal runaway (TR) has emerged as a critical challenge for the practical implementation of lithium-ion batteries (LIBs) in electric vehicles and energy storage systems. This paper examines thermal runaway propagation (TRP) in NCM pouch LIBs under two operating conditions: different state of charge (SOC) and spacing. Based on the results of various SOC experiments conducted without spacing, it is evident that the TRP time decreases significantly as the SOC increases. Additionally, there is a gradual increase in the maximum temperature and mass loss rate of the module and more intense flame ejection behavior. Furthermore, the TRP interval and duration gradually increase with increasing spacing. In comparison, different SOC has a more pronounced effect on maximum temperature, mass loss, and flame ejection behavior of the module than changes in spacing do. Heat transfer analysis shows that the main source of heat before TR is mainly contributed by the previous cell, which accounts for 35.3 %–72 % of the total heat absorbed by the cell. This study offers guidance for further characterization studies and safety measures of the LIBs TRP.