Research On Low-temperature Heating Of Lithium Battery Based On Lithium Plating Electrochemical-thermal Coupling Model

Lithium-ion batteries have become the main power source of electric vehicles due to their high energy density,high voltage platform,and long cycle life.However,the poor low-temperature performance of lithium-ion batteries also restricts the further development of electric vehicles.In a low temperature environment,not only the discharge capacity of lithium-ion batteries is severely attenuated,but also the charging capacity is greatly reduced.Lithium plating may occur at the end of charging or during high-current charging,which affects the safe use of the battery.Starting from the electrochemical reaction mechanism,thesis establishes an electrochemical thermal coupling model that takes in to account the lithium plating reaction.After comprehensively verifying the accuracy of the model,the low-temperature performance of the lithium-ion battery was analyzed in terms of temperature and electrochemical physical quantities,and the conditions for lithium plating during lowtemperature charging of the battery were clarified,and an alternating current heating strategy to suppress lithium plating was designed.The research content of this thesis is carried out from the following aspects:1.Based on the pseudo-two-dimensional(P2D)model of lithium-ion battery,an electrochemical model considering the lithium plating reaction and the electric double layer effect is established,and coupled with the thermal model through the temperature sensitive parameters in the electrochemical model.Using finite element software to realize the full three-dimensional simulation of lithium iron phosphate pouch cell.2.Basic performance experiments for the selected experimental batteries,including constant current charge and discharge experiments at different temperatures and different rates,dynamic stress test experiments at different temperatures,and lithium plating analysis experiments.These experiments are used to verify the accuracy of the model built in this paper.3.The full three-dimensional coupling model is used to simulate the temperature field distribution of the battery,and the temperature distribution difference between the internal cell unit and the surface cell unit is compared.At the same time,it simulates the changes of some unmeasurable electrochemical physical quantities such as electrode current density,negative lithium intercalation concentration,anode solid-liquid phase potential during low-temperature charging of lithium-ion batteries,realizing quantitative analysis of battery internal physical quantities.4.By analyzing the low-temperature performance of the lithium-ion battery,it is found that the lithium plating reaction first occurs at the interface between the negative electrode and the septum,and according to the change in the lithium plating overpotential of the interface,the time when the battery undergoes lithium plating under different lowtemperature charging conditions is obtained through simulation.Then analyzed the lithium plating situation in the electrode plane of the large-capacity battery,and pointed out that the lithium plating reaction is prone to occur where the current density is large.5.Comprehensively consider the lithium plating reaction and heating rate,determine the waveform,frequency and amplitude of the alternating current,design a multi-stage heating method that changes the AC amplitude with temperature changes.Achieve the heating target of raising the battery temperature from-20°C to 10°C within12 minutes without lithium plating.