Electrochemical Modeling And Simulation Of Lithium-ion Power Battery

Performance of power batteries for electric vehicles has significant impact on vehicle dynamic properties, endurance mileage and security. For a better battery performance, it is necessary to ensure accurate estimation of state of charge and state of health, precise life prediction, and safe and stable battery operation, which are all closely related to the veracity of the power battery model. Therefore, establishing an accurate battery model is important for battery research. For analysis of battery internal reaction mechanism, the establishment of battery simulation model can reduce power consumption of actual battery in experiments. For determination of control requirements and control strategy, battery model can greatly reduce the span and costs of one design cycle. For the thermal management of battery, a precise simulation model can help analyze the temperature changes inside the battery to prevent thermal abuse. For the equilibrium management of battery, an accurate simulation model is beneficial to accurately obtaining the equilibrium parameters, like battery terminal voltage and state of charge. Thus, accurate model is necessary for battery analysis and research. This paper focuses on electrochemical modeling and simulation of the lithium-ion battery, and it can be summarized as the following aspects:Firstly, the background knowledge and significance of lithium-ion battery electrochemical modeling are introduced. According to the references at home and abroad, research status of electrochemical modeling, model simplification and parameters identification for lithium-ion battery are described.Secondly, the internal structure and working principle of lithium-ion battery are introduced. Then, the single particle model of lithium-ion battery is set up according to the porous electrode theory, concentrated solution theory, Fick’s law and Butler-Volmer kinetic equation. The partial differential equations for the diffusion of lithium-ions in single particle model are simplified into ordinary differential equations and algebraic equation using three parameters parabolic method, and then the simplified single particle model is obtained.Then, as the research object, A123 lithium iron phosphate batteries are discharged by charging and discharging equipment to obtain the battery terminal voltage data. Then open circuit voltage expression of the positive electrode is fitted by the experimental data. Because of the immeasurability, other parameters are identified using bacteria foraging optimization algorithm, such as positive electrode and the negative electrode surface area of the active region, positive electrode and negative electrode lithium-ion diffusion coefficient, and positive electrode and negative electrode reaction rate constant.Lastly, the proposed model is testified by simulation and comparison experiments. The proposed single particle model of lithium-ion battery is built in Matlab/Simulink for simulating, with the fitted positive electrode open-circuit voltage expression, the empirical formula of negative electrode open-circuit voltage, and parameters obtained by identification process and references. Accuracy of the single particle model is verified by comparing the terminal voltages obtained from experiments and single particle model under constant current discharge mode, varying current mode and New European Driving Cycle, respectively. The sources of error have also been analyzed. Finally, accuracies of the equivalent circuit model, the electrode averaged model and the proposed single particle model are compared and then battery discharge performances are analyzed based on single particle model.