Estimation Of Electrochemical Parameters Of Li-ion Battery And Prediction Of Internal Temperature

In recent years,lithium-ion batteries have been widely used in the field of grid energy storage and electric vehicles.Lithium-ion batteries are subject to thermal runaway due to operating conditions.One of the direct causes of thermal runaway is the internal overheating of the battery,and accurate sensing of the internal temperature is essential to prevent thermal runaway.It has been shown that Electrochemical Impedance Spectroscopy(EIS)is a characterization of the battery properties and the internal temperature is expressed in EIS.In this thesis,an impedance external characteristic-key electrochemical parameter-internal temperature model is developed to achieve internal temperature prediction by investigating the key electrochemical parameters that play a dominant role in the variation of EIS with internal temperature.The main research works are as follows.(1)Combined with the electrochemical impedance spectrum theory,electrochemical impedance measurement experiments were carried out on 18650 type lithium iron phosphate battery as the main research object,and the EIS characteristics of the battery under different conditions were analyzed.The results show that the internal temperature has a significant effect on the EIS,and the charge transfer impedance decreases with the increase of the internal temperature,while the State of Charge(SOC)has a small effect on the EIS shape.The results provide data to support the subsequent investigation of the role of each electrochemical parameter in the process of internal temperature influencing impedance,and to fit the electrochemical parameters under each condition.(2)Based on the modeling principle of pseudo-two-dimensional model,an electrochemical model was established in COMSOL Multiphysics,and the electrochemical parameters were fitted to make the output impedance curve of the model consistent with the experimental results,and the variation law of the electrochemical parameters with the internal temperature was analyzed.The results show that two key electrochemical parameters,namely,the positive exchange current density and the positive tortuosity Bruggeman coefficient,are influenced by the internal temperature and play a dominant role in the variation of the EIS with the internal temperature.By analyzing the correlation between the above key electrochemical parameters and SOC,the anode tortuosity Bruggeman coefficient,which is independent of SOC and has a strong ability to characterize the internal temperature,is determined as the basis for internal temperature prediction.(3)The impedance-critical electrochemical parameter-internal temperature model was established by quickly obtaining the Bruggeman coefficient of anode tortuosity at different temperatures from the impedance amplitude of a single frequency point in the low frequency band and combining the calibration relationship between this parameter and the internal temperature.Subsequently,experiments were designed to validate the above model,and the results showed that the model can predict the internal temperature in the full temperature range,and the error can be basically controlled within 1℃ in the high temperature range above 40℃ to meet the engineering needs.Compared with the traditional impedance-based internal temperature prediction method,the prediction method in this thesis has advantages in accuracy and generalizability,and can be applied to batteries of similar electrochemical systems.