Study On Thermal Runaway Characteristics And Modeling Of Large-format Lithium-ion Batteries Under The Full Range Of State Of Charge

Thermal runaway（TR）problem of lithium-ion batteries（LIBs）is a critical factor hindering the large-scale application of LIBs.With the continuous energy density raising of lithium-ion battery,LIBs are easy to get thermal runaway at the full range of state of charge（SOC）.Thermal runaway of LIBs cause smoke,fire,and even explosion,threating severely human life and property.Research on thermal runaway behaviors and countermeasures of cell and module at different SOC have a great significance on public property safety.This thesis studies thermal hazard assessment of LIB with different system under the full range of SOC,thermal–electric coupled TR model of high-nickel batteries under the full range of SOC and thermal runaway propagation（TRP）experiments and modeling of medium-nickel battery module under different SOC.This research provides reference and idea for the study of thermal runaway problem of LIBs under the full range of SOC.Firstly,focusing on the thermal runaway problem of LIBs at different SOC,accelerating rate calorimetry（ARC）is used to compare with the thermal hazard of three different system LIB after thermal runaway.Then,the relationship between TR characteristic parameters and SOC is explored.Secondly,based on the results of adiabatic TR experiments at different SOC,the relationship between TR characteristic parameters and SOC is got.The coupling relationship between temperature and voltage is established by defining two new parameters c_chem and c_eq.And then the coupling relationship between concentration field and SOC is used to construct the thermal-electric coupled TR model of LIB.The feasibility of the dual-coupling paths is verified.Based on the model analysis results,the feasibility of using normalized concentration to simulate other characteristic signals of TR is discussed.Finally,research on the thermal runaway propagation（TRP）and modeling of NCM523 module under different SOC is carried out.The sequence of different trigger signals is compared,the results can help researchers to select the TR identification signals for LIB.Then,the method of in-situ measurement and optimal identification are combined to acquire the thermal properties parameters of the battery jellyroll.The thermal properties parameters are used to construct the TRP model of the NCM523battery module.The experimental results are used to verify the accuracy of the TRPmodel under different SOC.Furthermore,the validated model is used to explore the thermal behavior of TRP modules under different SOC and different heat production under a specific SOC.The simulation results proved that the determinant of TRP is the peak transfer power P_i,i+1 instead of the heat transfer Q_i,i+1.The results also indicate that there are three different ways of TRP,this conclusion provide theoretical guidance for the inhibition and even blocking of module TRP.