Application Of The Mechanism Model In The State Estimation And Prediction Of Lithium Ion Battery

The accurate estimation and prediction of the lithium ion battery state is of great significance to improve the reliability of the battery and optimize the control strategy.Based on the mechanism model,the relationship between the internal characteristics and the external signal of the battery is analyzed under different types of batteries and different applications.The method of state estimation and performance prediction for lithium ion batteries was studied.Based on the mechanism model analysis method,the internal state of the battery is estimated by analyzing the external response of the battery,and a battery state estimation method based on material characteristics is proposed.First of all,the solid diffusion coefficient of some materials changes in the working process,and the electrochemical model was modified to establish the variable solid state diffusivity.Then,according to the huge difference of the solid diffusion coefficient between the surface and the interior of the material during the working process,and the rapid change of the surface concentration,a method was established by short time excitation to distinguish the SOC(state of charge)of the battery.The method can be used to distinguish the LiFePO4 batteries with different SOC in the voltage platform,so as to improve the consistency of the battery system.Based on the mechanism model analysis,the degradation process of the battery is studied by analyzing the evolution of the internal state of the battery,and a quantitative and qualitative analysis method for the blended electrodes is established.According to the characteristics of the blended electrode,the mechanism model of a lithium-ion battery with a blended electrode was established on the basis of the electrochemical model,and the equilibrium model of composite electrode was established by neglecting the polarization process inside the battery.Based on the established models,the relationship between the external characteristics and the internal state of the battery containing the blended electrode is studied.According to the characteristics of the blended electrode equilibrium potential and its differential curve,the accurate analysis of the state of the blended electrode is realized.In addition,we use the established models to analyze the storage and cycling performance and the aging mechanism of a lithium ion battery containing a blended electrode.The degradation of the systems with blended electrode is the result of the synergistic effect of the materials in the electrode,and shows different features in different stages of degradation.Based on the mechanism model analysis method and the degradation mechanism of the battery,the battery capacity prediction is studied,and an analytical method for the capacity decay of lithium ion batteries in storage is established.A pseudo open circuit voltage model of a lithium ion battery is developed to investigate the evolution of internal parameters,and a degradation model is developed that can be used for predicting the calendar life of the battery.The good agreement between the calculated and experimental results is the evidence that the models are able to accurately capture the degradation process of the battery.In addition,we use both incremental capacity and differential voltage analysis to analyze the aging mechanism of a lithium ion battery.Our results revealed that the capacity fading during the aging process is predominantly caused by the loss of Li-ions and self-discharge.Based on the mechanism model analysis method,the effect of polarization on the battery behavior is introduced,the prediction of the whole performance of the battery is studied,and the analytical method for the performance degradation of Li ion batteries is proposed.In order to identify the internal state of the battery,while retaining the main characteristics of the internal process of the battery,the electrochemical mechanism model was simplified and a simplified mechanism model was established.Based on the simplified mechanism model,the capacity and power degradation of lithium ion battery were studied,and the method for predicting the performance of the battery was developed based on the evolution of the battery capacity and polarization parameters.In addition,according to the process development of the corresponding software,the automatic processing of data analysis was realized.