Study On Modeling And Thermal Characterization Of Aging Lithium-ion Batteries

With the increasing demand for environmental protection and sustainable development,new energy vehicles,as a green mode of transportation,are receiving more and more attention and promotion.Lithium-ion batteries are widely used in the new energy vehicle industry due to their high energy density,large output power,and low self-discharge rate.However,the electrical performance and thermal characteristics of lithium-ion batteries deteriorate during the working cycle,which seriously affects the safety and stability of new energy vehicles.Therefore,understanding the evolution of the electrical performance of lithium-ion batteries during the aging process and the impact of aging on the heat generation mechanism is crucial for achieving good management of batteries throughout their entire life cycle.This paper focuses on the electrical performance and thermal characteristics of lithium-ion batteries under aging conditions,establishes an electrochemical aging model,and an electrochemical-aging-thermal coupling model for lithium-ion batteries.The objective is to predict the performance of lithium-ion batteries under aging conditions and provide theoretical and practical guidance for good management of lithium-ion batteries throughout their entire life cycle.The main research contents of this paper are as follows:(1)The structure and working principle of lithium-ion batteries were analyzed,and a lithium-ion battery cycling experimental platform was established,mainly including the computer control unit,battery charge-discharge tester,and high-low temperature chamber.The discharge characteristics,capacity characteristics,cycle aging characteristics,and temperature rise characteristics of lithium-ion batteries were designed and tested.A large amount of lithium-ion battery data was obtained through the above tests,laying a foundation for the establishment of lithium-ion battery models.(2)The aging and degradation mechanism of Li-ion batteries was described,and an electrochemical aging model of Li-ion batteries was established,which considered the degradation and aging of Li-ion batteries caused by the side reaction of SEI film growth.Under the condition of constant current discharge,parameter identification is carried out by COMSOL and MATLAB co-simulation and genetic algorithm.The model was verified by constant current experiments with different ratios(0.5C,1C,1.5C,2C)at 25℃.Although there were errors in the voltage,the maximum errors were 2.016%,2.583%,3.464%and 4.209%,but the variation trend was the same,and the model had good accuracy.(3)In order to study the thermal behavior of lithium ion batteries,a cylindrical radial double-layer structure of lithium ion batteries was established to identify the thermal physical parameters(specific heat capacity,thermal conductivity and convective heat transfer coefficient)of lithium ion batteries by using genetic algorithm.Thermal physical parameter values are respectively 1038.8 J/(kg?K),2.3 W/(m?K),and 10.5 W/(m~2?K).(4)The heat generation and heat exchange principles of lithium-ion batteries were analyzed,and an electrochemical-aging-thermal coupling model for lithium-ion batteries was established.Dynamic parameters were corrected using the Arrhenius formula,and the model was experimentally verified by temperature rise tests at different discharge rates(0.5C,1C,1.5C,2C)at 25°C,with maximum errors of about 0.853°C,0.995°C,2.04°C,and 3.63°C,respectively.