Research On Discharge Characteristics Analysis And Internal Temperature Estimation Method Of Lithium-ion Battery

With the diversification and complexity of lithium-ion battery application scenarios,the performance degradation and safety issues caused by the service process have attracted more and more attention.In particular,the comprehensive analysis of battery characteristics changes during the discharge process is not clear,and the internal temperature is inaccurately estimated.In-depth research on these issues is the key to develop efficient battery management systems to ensure the excellent performance and safety of battery.Therefore,this paper conducts corresponding research on the characteristics changes and internal temperature estimation of lithium-ion battery during discharge.The main research contents are as follows:(1)The theoretical relationship between lithium-ion battery characteristics and current and the theory of battery thermal model are studied.The relationship between lithium-ion battery capacity and current is analyzed by Peukert theory.The internal resistance parameters of the second-order RC equivalent circuit model of the battery are identified based on the recursive least squares method with forgetting factor,and the voltage changes during the discharge process are analyzed.The thermal model theory of the battery is studied,the heat generation and heat transfer principles of the battery are analyzed,and the three-dimensional thermal model of the battery is deduced according to the law of conservation of energy.(2)Aiming at the problem of unclear comprehensive analysis of changes in discharge characteristics of lithium-ion battery,constant current discharge experiments and hybrid power pulse characteristics experiments are carried out at the discharge rate of 0.5C～4C.The influence of the discharge rate on the battery capacity,internal resistance,voltage and surface temperature in different regions is analyzed,and their variation laws are studied.The results show that the battery capacity is sensitive to the discharge rate.At high discharge rates,the battery capacity drops sharply.As the discharge rate increases,the total internal resistance of the battery decreases,and the ohmic internal resistance accounts for an increasing proportion of the total internal resistance.When the battery is discharged at high rates,the terminal voltage in the initial stage will drop rapidly and then rise again due to the concentration polarization,and this phenomenon will become more significant with the increase of the discharge rate.At the same time,the increase of the discharge rate will lead to the increase of the temperature of the battery surface and the acceleration of the temperature rise rate,and the inhomogeneity of the temperature distribution intensifies.(3)Aiming at the problem of inaccurate estimation of the internal temperature of lithium-ion battery,considering the non-uniformity of battery temperature distribution,a new non-uniform heat generation model based on regional voltage is proposed to estimate the internal temperature distribution of battery in real time.According to the size and thermal characteristics of the selected lithium cobalt oxide soft-pack lithium-ion battery,the battery is divided into nine regions.The regional voltage is calculated from the regional surface temperature and ambient temperature data measured during each 0.1 state of charge drop,and then the regional heat production power of the battery is determined.And establish a three-dimensional numerical simulation model to simulate the spatial distribution of the battery internal temperature.It is verified by experiments that the error between the estimated temperature and the measured value is within 1 °C,indicating that the model can effectively estimation battery temperature distribution.Finally,according to the the internal temperature estimation results obtained by the non-uniform heat generation model,the spatial evolution laws of battery temperature at discharge rates of 0.5C,1C,2C,3C and 4C is analyzed.