Research On Electrochemical-Thermal Characteristics Analysis And Optimization Of Automotive Ternary Lithium-ion Battery

As one of the mainstream energy storage devices for electric vehicles,ternary LIBs?lithium-ion batteries?have attracted much attention due to their electrochemical and thermal performance.A single electrochemical model has obvious disadvantages as a transient model due to the continuous temperature change of the battery during the working process.Some key parameters in the electrochemical model are greatly affected by temperature changes.The electrochemical model is coupled with the thermal model to obtain accurate transient output,so that the parameters of the battery can be accurately analyzed and optimized.Therefore,based on the electrochemical-thermal coupled model,a 3D finite element model is established to analyze the electrochemical,thermal characteristics and optimize the thermal related parameters of the battery.The specific research work is as follows:Firstly,the electrochemical performance of the 40Ah ternary prism LIBs of vehicles were tested,the curves of capacity-voltage,time-temperature,direct internal resistance and DST driving condition were obtained to confirm the electrochemical performance of batteries and provide reference data for the subsequent model validation.Secondly,based on the obtained experimental data,a precise 3D electrochemical-thermal average coupled finite element model of 40Ah lithium-ion prismatic battery for vehicle was established by means of COMSOL Multiphysics software.The model presented good accuracy in both constant current discharge and transient heat performance.At the same time,the experimental results are in good agreement with the simulation results under DST condition verification,which fully proved the accuracy and validity of the model under constant and variable current conditions.Thirdly,based on the established model,the selected 6 battery material and structural parameters were analyzed in detail by means of parametric scan.The 6 parameters analyzed are current C-rate C,battery thickness Th_bat,initial ambient temperature T_int,positive porous electrode thickness Th_pos,positive electrode particle diameter D_pos,positive electrode solid phase volume fraction?_1,pos.In order to provide a reference for subsequent optimization,the influence of the parameters on the discharge curve,electrolyte concentration distribution,Von Mises Stress distribution and current density distribution were mainly studied in the aspect of electrochemistry.Moreover,the effects of parameters on the overall and local heating power,overall temperature rise and temperature distribution and so on were also mainly discussed in the aspect of thermal characteristic analysis.Finally,the above 6 parameters and the overall average temperature rise were optimized.According to the experimental data of the model,the response surface fitting of battery parameters was carried out by means of variance analysis and the optimized design parameters were sought.The advantages in heating were verified by the single finite element model,and the improvement of thermal performance in practical application was verified by establishing the finite element model of conjugate heat transfer battery module.After the optimization,the temperature of the battery dropped by 13.22%,the temperature of the conjugate-coupled battery module dropped by 26.89%.The module center temperature decreased significantly,and the temperature distribution was more dispersed,which was conducive to heat dissipation.