Electrochemical-thermal Characteristics Analysis And Optimal Design Of Ternary Lithium-ion Battery For Electric Vehicles

The ternary cathode lithium-ion batteries possess excellent electrochemical performance.Thus,in recent years,the ternary cathode lithium-ion batteries are more preferred over the other battery chemistries as the power source for electric vehicles.However,their internal electrochemical phenomenon and thermal characteristics cannot be analyzed by the experimental studies.Thus,it is necessary to use a numerical technique to solve these challenges.As temperature influences some specific parameters in the electrochemical model,thus,it is difficult for the electrochemical model alone to achieve accurate and reliable results because of incessant change in the temperature of the battery during its dis?charging?.Hence,it is essential to establish the coupling between electrochemical and thermal models.Thus,in this work,based on the coupling between the electrochemical and thermal models,a 3D finite element average electrochemical-thermal coupled model is developed to study the electrochemical and thermal characteristics of the battery.Furthermore,the multi-parameter optimization technique is used to improve the thermal performance of the battery.The main research content is as follows:Firstly,the 30 Ah ternary cathode automotive lithium-ion battery is selected as the research target,and various performance tests,including DCR?Direct Current Internal Resistance?tests and discharge tests are performed on it to ensure its electrochemical performance meets the requirement of the study.The reference data obtained from these tests,i.e.,voltage change and temperature rise during discharge are used to verify the subsequent model.Secondly,a 3D finite element average electrochemical-thermal coupled model for 30 Ah battery is developed on the COMSOL Multiphysics^?5.4,and its accuracy and effectiveness are verified with the experimental data.The model shows consistent results with the experimental discharge and temperature rise curves,which verifies its effectiveness and reliability to simulate accurate results.Thirdly,by using a developed 3D coupled model,the influence of the six-battery geometrical and material parameters on the internal electrochemical phenomenon and thermal characteristics are analyzed and discussed in great detail.The discharge rate C,initial/operating temperature T_initial,thickness of battery L_bat,particle diameter of positive electrode active material d_pos,thickness of the positive electrode L_pos and volume fraction of the solid-phase in the positive electrode?_s,pos are six selected parameters for the study.Since the focus of the study is on ternary cathode LIB,thus,only parameters related to positive electrode are selected for the investigation.From the perspective of electrochemical performance,the effect of the selected parameters on the discharge capacity curve,distribution of electrolyte and lithium-ion concentration along electrodes,distribution of the Von Misses Stress along the normalized active material particle radius and distribution of the current density in the unit cell are investigated using parametric scanning.Furthermore,from the perspective of thermal characteristics,the influence on the heat generation in the unit cell and its every part,change in battery temperature with capacity and thermal distribution are investigated.The results show that the C and T_initial have a significant influence on the discharge capacity and voltage of the battery.The heat generation in the metal parts of the unit cell is correlated with the current density.The heat dissipation ability of the battery reduces with increase in aspect ratio,which leads to heat accumulation,thermal gradient and temperature of the battery.The effect of the solid phase volume fraction is found to be same as electrode thickness.The higher heat transfer coefficient improves safety and reduces the temperature the battery,but also causes the inhomogeneity among the electrochemical and thermal characteristics.Finally,the above parameters are optimized to improve the thermal performance of the battery.In this process,the multi-parameter optimization model combined with Response Surface Methodology?RSM?is used to minimize the battery temperature rise.The optimal values of the parameters are used in the battery model to ensure the reliability of the multi-parameter optimization model.It is found that after the optimization,the battery temperature rise is fallen by 10%.