Research On Internal Temperature Estimation And Thermal Optimization Design Of Ternary Lithium Battery

Ternary lithium ion power battery has attracted extensive attention from enterprises and researchers in recent years due to its high energy density,high voltage platform and good cycle performance.However,when the energy density is high,ternary power battery heating is more serious,internal temperature and surface temperature are not consistent,so it is necessary to study the internal temperature of ternary battery.On the one hand,the internal temperature needs to be estimated in real time in the aging process,and the battery is often in the condition of rapid temperature change in some areas,so the influence of rapid temperature change on aging should be fully considered.On the other hand,with the upsizing of three-way batteries,heat is easy to accumulate rapidly,which will lead to excessive internal and external temperature differences and internal temperature,which will affect the performance of batteries.Therefore,internal temperature and temperature differences need to be optimized.In view of the above two problems,the research work of this paper is as follows:Taking Li[Ni_0.8Co_0.15Al_0.05]O₂（NCA）battery as the research object,a cylindrical NCR18650 battery cycle platform was built,and an alternating temperature experiment was designed to obtain the battery capacity,internal resistance,open circuit voltage and other characteristic parameters under different cycles,which provided experimental verification for the estimation of surface temperature in the following chapter..The temperature field of lithium-ion battery is analyzed and simplified,and the second-order equivalent thermal resistance network model is selected.The parameters of the thermal resistance network model are identified by using the least square method and thermal shock experiment.Finally,the temperature of the battery under different aging states is estimated by using the extended kalman filter algorithm,which is verified by experiments.The verification results show that the maximum estimation error of surface temperature is within 1℃.Li[Ni_1/3Co_1/3Mn_1/3]O₂（NCM）battery was used as the research object,and COMSOL Multiphysics 5.5^?was used to establish the three-dimensional electrochemical-thermal coupling model of 37Ah ternary square shell power battery.The accuracy is verified by voltage and temperature curves in references.Based on the three-dimensional electrochemical-thermal coupling model,seven parameters,including solid volume fraction of positive electrode,thickness of positive electrode,particle radius of positive electrode,cell thickness×width,thermal conductivity,discharge rate and convective heat transfer coefficient,were parameterized.The results show that the positive electrode particle radius has little influence on temperature and temperature difference.Finally,the remaining six parameters are used as subsequent temperature field optimization parameters.The experimental design software Minitab 2019^?was used to construct the response surface model.The experimental factors were selected as six parameters,and the objective functions were maximum internal center temperature（MICT）and maximum center temperature difference（CMTD）.The reliability and accuracy of the model are proved by variance analysis.The effects of interaction factors on MICT and CMTD were analyzed.Then,taking the constant current in 3C as an example,the optimized MICT and CMTD are set at 45℃and 2℃respectively.Finally,the optimized parameters were substituted into COMSOL Multiphysics5.5^?to calculate,and the maximum error range between simulation values and optimized values was within 1%.Compared with the initial value,MICT and CMTD decreased by 9.5%and62.1%,respectively.