| During the working process,there are both diffusion-induced stress(DIS)and thermal stress(TS)in lithium-ion batteries(LIBs).Their comprehensive effect can cause various mechanical damage to the structure and material in the battery,thus resulting in the capacity decay and life shortening of the battery.At present,the research on the stress at the battery scale is mainly based on the experiment method.Howerver,it is not only time-consuming and hard to repeat,but also unable to obtain the distribution and change of the stress in the battery.If the stress field in the battery during charge and discharge process can be obtained by the simulation method,the main factors affecting the stress field and the effective methods to reduce the stress level can be analyzed and discussed by the numerical calculation,so as to extend the cycle life of LIBsIn this paper,a pouch ternary LIB is taken as the research object,and the cycle experiment platform of the battery is built.The temperature experiment,DIS experiment and overall stress(OS)experiment of the battery during three charge and discharge cycles are carried out.The changes of the voltage,the temperature of measuring poin ts and the stress on the battery surface with the time are obtained.The experiment results show the high-temperature area on the battery surface gradually transfers from the positive tab to the center during the constant-current(CC)charge and discharge processes.The stress on the battery surface increases gradually during the charge process but decreases gradually during the discharge process.At the end of discharge,the stress on the battery surface is slightly higher than the initial external pressure,the irreversible volume expansion occurs in the battery.The progressive modeling method is used in this paper to lower the complicacy of the modeling process and fully verify the validity of the model.Firstly,a 3D electrochemical－thermal coupling finite element(FE)model of the LIB at the multiple scale is built in COM SOL Multiphysics,and the model effectiveness is verified.The electrochemical performance and thermal performance of the battery during 1C CC charge process are studied by the validated model,including the distribution of the current density,potential and lithium-ion concentration,the heat production rate of each battery component,and the temperature distribution of the battery.The results show during the whole charge process,the maximum temperature ’of’the battery appears at the center area of the battery at the end of charge.Then,a 3D electrochemical-mechanical coupling FE model of the LIB at the multiple scale is built in COMSOL,and the model effectiveness is verified.The mechanical performance of the battery during 1C CC charge process is studied by the validated model,including the distribution of the displacement,diffusion-induced strain and DIS.The results show with the increase of the charge time,the maximum DIS and the average DIS increase rapidly first,then remain unchanged,and finally increase slowly.During the charge process,the maximum DIS in the battery appears at the interior area of the positive active layer at the end of charge.Finally,a 3D electrochemical-thermal-mechanical coupling FE model of the LIB at themultiple scale is built in COMSOL,and the model effectiveness is verified.The mechanical performance of the battery during 1C CC charge process is investigated by the validated model,including the distribution of the displacement,thermal strain,TS,,overall strain and OS.The results indicate the OS in the battery is not equal to the simple sum of the DIS and the TS,but the comprehensive effect of them.During the whole charge process,the maximum TS in the battery appears at the center area of the positive current collector at the end of charge.During the whole charge process,the maximum OS in the battery appears at the interior area of the positive active layer at the end of charge,which is the most prone to the mechanical damage. |
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