Study On Electrochemical-thermal Characteristics Of Ternary Cylindrical Lithium Ion Batteries For Automotive

With the improvement of power battery energy density the use of the vehicle is promoted,but the frequent occurrence of battery spontaneous combustion accidents in electric vehicles restricts the further development of electric vehicles,battery thermal management as a key technology of electric vehicles is able to improve the safety of battery.Therefore,it is of great significance to explore the characteristics of power battery for battery safety.This paper mainly studied the electrochemical and thermal characteristics of cylindrical lithium ion batteries from the following aspects,including battery performance test and analysis,electrochemical and thermal coupling model construction,electrochemical and thermal characteristics research,and optimized the internal structure size of the battery.The main research contents and conclusions are as follows:Firstly,the electrochemical and thermal characteristics of cylindrical ternary lithium ion batteries are tested,including electrode reference potential test,battery overvoltage test,Hybrid Pulse Power Characteristic(HPPC)test,battery discharge test and temperature monitoring under different operating conditions,and thermal coefficient test.The analysis of the test results show that discharge capacity is subject to C rate and environmental temperature,large C rate and low temperature will lead to discharge capacity decline,this is because of the battery internal resistance and polarization increase,so the working conditions for the battery is very important.Through further research,it is found that the battery discharge capacity is large and the temperature increment is minimal when the rate is 1 C at room temperature of 25 °C,which can be used as the best working condition for the long-term stable operation.Secondly,the battery electrochemical-thermal coupling model is set up by the experimental data and tested parameters,and the accuracy and reliability of the model were validated with tested data under different working conditions,found that the battery discharge curve of maximum error is 1.4% and temperature maximum error is 4.26%,the model has high precision and good applicability in this paper compared with others' model and can be used for further research.Then he electrochemical characteristics of the battery was explored based on the model.The research results showed that the size of electrode particles and C rate affected the concentration polarization.When the particle size of the positive electrode increased,the concentration polarization of the battery increased.In order to reduce concentration polarization and increase discharge capacity,the particle size of positive electrode was optimized,and it was found that the target conditions could be satisfied when the radius was 3 ?m.Further study on the electrochemical characteristics of the battery and optimization of the internal structure size ofthe battery,showed that the discharge capacity of the battery increased gradually with the increase of the thickness of the positive electrode,while the discharge capacity remained previous value when the thickness of the negative electrode and separator was changed.The thickness of the negative electrode affects the discharge voltage,and the discharge curve has a higher voltage platform when the thickness is 70 ?m,so the thickness value can be used as the best choice for the coating of the negative electrode material.The coating thickness of the positive electrode material is generally lower than that of the negative material.Finally,the thermal characteristics of the battery are studied based on the model.The results show that the total heat produced by the battery includes reversible heat and irreversible heat,and some of the reversible heat is endothermic reaction.Through further analysis,showed that reversible heat mainly comes from the negative pole but irreversible heat mainly comes from the positive pole,and heat production is the highest at the interface between electrode and separator,and the lowest at the current collection area.The heat production of positive and negative electrodes is affected by the internal parameters of the battery.It is found that when the specific surface area of the particles of negative electrode is reduced,the negative electrode will accelerate to the peak of heat absorption.When the reaction rate constant of positive electrode is reduced,the positive electrode irreversible heat will increase.It is found that when the heat transfer coefficient h = 15 can be used as a reference value in the design of thermal management of the battery.At this time,the discharge capacity of the battery is larger and the temperature is lower.