Study On The Effect Of Thermal Accumulation On The Parameters Of Li-ion Batteries

In recent years,the development of electric vehicle industry has been strongly supported by all countries in the world.As the main power source of electric vehicles,lithium-ion batteries have attracted wide attention in their rational use and safety.Because of the airtightness of the battery,the internal heat produced in the working process can't be discharged in time,resulting in heat accumulation effect and large temperature difference inside and outside the battery.This phenomenon is especially obvious in the case of high rate charge and discharge.The thermal management will be ineffective if the internal temperature of the battery cannot be obtained accurately,which will bring greater safety risks.The equivalent circuit model parameters of the battery are the basis of the state estimation of the battery.At present,the ambient temperature is used as the basis for calculating the battery state estimation.In case of a large gap between the battery internal temperature and the ambient temperature,this calculation method will lead to an increase in the estimation error of the model parameters and then affect the battery estimation of state of charge(SOC),state of power(SOP)and state and health(SOH).Therefore,the accurate estimation of the battery internal temperature is very important for the accuracy of the battery model,the accuracy of the battery state estimation,and the safety protection and reasonable use of the battery.For the unavailable internal temperature of lithium-ion battery,a thermal model for the estimation of battery internal temperature was first established based on Conservation of Energy,Fourier's Law and Newton's Law of Cooling after analyzing the mechanism of the working current heat production of the battery,the heat accumulation process of the battery and the influence of the ambient temperature on the heat conduction.Electro-thermal-parameters model was established on this basis.Second,a simple and accurate thermal insulation experiment was designed,the parameters of thermal model were identified,and the accuracy of thermal model was verified by RK4 algorithm;Finally,the influence of the battery internal temperature on the battery model parameters was studied,the TEC-Arrehnius model for internal temperature and model parameter was established based on electric-thermal model and the Improved Thevenin model was proposed considering internal temperature and SOC.The results suggest that the thermal model can accurately estimate the internal temperature of the battery with an estimation error of less than 0.5?;Compared with the traditional model which only considers the ambient temperature,the Improved Thevenin model considers the parameter model output of internal temperature that is closer to the real value,which verifies the reliability and accuracy of the proposed model.Battery thermal model and Thevenin model proposed in this paper can provide strong support for battery thermal management and high-precision state estimation.