Modeling And Simulation Research On The Thermal Runaway Propagation Of Lithium-Ion Batteries Considering Combustion Reactions

Mainstream electric vehicles generally use lithium-ion batteries as power batteries.However,the thermal runaway of lithium-ion battery and its propagation can easily lead to fire accidents,which seriously threaten the safety of life and property of drivers and passengers.In order to reduce the harm of thermal runaway,the power battery pack needs to be reasonably designed to reduce the risk of thermal runaway propagation.Simulation analysis can verify the design scheme with low cost and high efficiency,which is helpful to realize the safe design of power battery pack.Therefore,studying the thermal runaway propagation modeling method and obtain the thermal runaway propagation characteristics of lithium-ion batteries through simulation is of great significance for improving the safety of the electric vehicle power battery pack.In order to determine the model parameters,a battery cell thermal runaway test platform was built to conduct thermal runaway tests on batteries with different states of charge(SOC),and the gas vented from the battery was artificially ignited.The thermal runaway and combustion characteristics of different SOC lithium-ion battery cells were obtained.The phenomena in the test process were compared,the temperature change law was analyzed,and the key parameters such as the opening time and opening temperature of the safety valve,the trigger time and trigger temperature of thermal runaway,the battery peak temperature and the maximum temperature rise rate,the combustion duration,and the ambient peak temperature were deeply studied.In order to strengthen the understanding of the mechanism of thermal runaway propagation,a thermal runaway propagation test platform was built to simulate the battery pack environment.The combustion reaction inside the battery pack was controlled by the gas guidance module.Experiments were carried out respectively with and without the exhaust guide module to explore the impact of battery combustion on thermal runaway propagation.The phenomena in the test process were compared,the temperature change law was analyzed,and the key parameters,such as the environmental peak temperature,the duration of environmental high temperature,the trigger time and trigger temperature of thermal runaway,the maximum temperature rise rate of the battery,and the battery peak temperature,were deeply studied.A thermal runaway propagation modeling method considering the combustion reaction was proposed.Taking the thermal runaway propagation test platform as the reference object,the geometric model of the battery pack was established and meshed;the initial conditions and boundary conditions of the model were determined according to the battery cell thermal runaway test results and the thermal runaway propagation test conditions.The battery safety valve was treated as dynamic boundary.The heat-flow-chemical coupling problem in the process of thermal runaway propagation is analyzed and the calculation scheme is determined.The simulation model is calculated,and the validity of the model is verified by the thermal runaway propagation test results.Based on the simulation model,the thermal runaway propagation characteristics were analyzed under the premise of considering the battery combustion reaction.The influence of battery pack structure parameters,battery surface emissivity and battery rupture mode on thermal runaway propagation was studied.The influence mechanism of various factors on thermal runaway propagation was deeply analyzed from the perspectives of battery temperature,gas temperature,oxygen concentration,combustion heat generation,gas flow rate,heat received by the battery,and heat released by the battery.Based on the simulation results,some suggestions on the design of battery pack were put forward.