Modeling And Internal Heating Strategies Of Lithium Ion Battery In Low Temperature Environment

With the further popularization of electric vehicles,lithium ion battery as the main power source has become the research focus of many scholars.The performance of lithium ion battery is affected by the ambient temperature.The low temperature environment leads to the decrease of the available capacity and the decline of external characteristics of the lithium ion battery.In this paper,the electrochemical-thermal coupling model is established to effectively describe the external characteristics of lithium ion batteries at low temperature.Based on the established model,the internal heating strategy of lithium ion batteries at low temperature is developed to effectively preheat lithium ion batteries at low temperature.Firstly,the working principle of lithium ion battery is described.According to the internal reaction of the battery,the classical pseudo-two-dimensional model is introduced,and the governing equations and boundary conditions such as solid and liquid diffusion of lithium ions in the battery,ohm’s law in the solid and liquid phase,charge conservation,electrode reaction kinetics and so on are established.Furthermore,the temperature adaptability of the pseudo-two-dimensional model is analyzed,and the fitting accuracy of the classical pseudo-two-dimensional model is concluded to be poor at low temperature.In this paper,the low-temperature model is established on the basis of the pseudo-two-dimensional model,the concentration of lithium ion is approximated by parabola,the governing equation describing solid and liquid diffusion is simplified according to the parabola,ohm’s law and charge conservation law are calculated,and the simplified electrochemical model is finally proposed.The heat production and dissipation conditions of lithium ion battery are analyzed,and centralized mass thermal model is established to describe the internal temperature variation of lithium ion battery.The parameters involved in the electrochemical model are updated according to the internal temperature of the battery during working process.An electrochemical-thermal coupling model is established.After the establishment of the electrochemical-thermal coupling model,it is necessary to identify the model parameters.Some model parameters are obtained by calculation,and the other parameters are obtained by genetic algorithm and least squares fitting.Finally,all parameters in the electrochemical-thermal coupling model were obtained.The model is validated under constant and dynamic conditions at253.15 K,263.15 K and 273.15 K temperatures.The results show that compared with the model without thermal coupling,the accuracy of the model is improved at the above three temperatures,up to 88%.And it can well fit the voltage trough phenomenon under253.15 K temperature.The model is also validated under constant and dynamic conditions at ambient temperatures of 283.15 K,298.15 K and 313.15 K,the results show that the model has ideal accuracy at normal temperature and high temperature.The low temperature model is further applied to the formulation of the internal heating strategy of the battery.The amplitude range of internal heating current is determined on the condition that lithium deposition does not occur in the cathode.The simulation is carried out at 10 Hz,50Hz and 100 Hz frequencies respectively,and the current condition and heating time used to heat the battery from 253.15 K to 278.15 K at three frequencies are obtained.The simulation results show that the internal heating strategy can preheat the battery effectively in 18 minutes.