The Numerical Simulation Of Electrochemical-thermal Behaviors Under Different Temperature In Lithium-ion Batteries

Lithium-ion batteries(LIBs)have been widely used as their excellent properties,such as the high voltage platform,high energy density,low self-discharge rate,long cycle life.The good performance of lithium-ion batteries precisely meet the requirements of current new energy automobile industry development.Still,LIBs have some disadvantages,such as battery low temperature performance,powerful performance and security problem,which restrict the widespread use of LIBs in other fields.The purpose of this paper is to establish an electrochemistry-thermal coupling model of LIBs for studying the electrochemical behavior and thermal behavior of LIBs during the process discharge.The relationships between LIBs electrochemical reaction and these factors that include diffusion migration relationship,temperature,and the design of the positive and negative electrode materials,having been discussed under the different temperature discharge.As well as,the influence laws of the LIBs discharge rate on thermogenesis,and thermal management system on the performance of LIBs.The main research work of this paper include:(1)Due to the complexity of LIBs,the discharge process of LIBs electrochemistry and internal heat interact.One dimensional electrochemical model and three dimensional electrochemistry-thermal coupling model are set up based on the key parameters in real time transfer,which obtain the process of LIBs discharge comprehensive electrochemical behavior and the distribution rule of temperature field.They show that temperature affect the diffusion of LIBs active material and electrolyte conductivity,on the contrary,the electrochemical reaction has important influence on the temperature under low discharge.(2)Under the normal temperature environment,the influence of LIBs electrochemical mass transfer,the discharge rate and cooling conditions on the distribution of LIBs temperature field are studied.During the process of discharge,in the thickness direction of electrode materials and inside the active particles,there are solid phase diffusion and liquid diffusion polarization,as discharging the two polarization are increased.The greater the active particle size is,the greater the diffusion polarization is,and vice versa.In the process of discharge,the highest temperature of LIBs appears in the center of the lower place,the temperature around the anode tab and cathode tab is lower than other places.At the low discharging rate,reversible heat plays a dominant role in the total heat,which appears endothermic andexothermic phenomenon during the discharge process.However,at the high discharging rate,the irreversible heat plays a leading role and the endothermic process disappears gradually.(3)On the basis of the normal temperature environment to discharge,the characteristics of LIBs discharge are studied under low temperature environment.Under the low temperature environment,the diffusion polarization of lithium ion is severe in low temperature,even get fully rest it is hard to reach balance.This characteristic results in the occurrence of massive evaporation of capacity and poor cycle performance of LIBs in low temperature.When the environment temperature is extremely low,the more serious the ohm polarization and concentration polarization are,the more heat LIBs are and the faster the temperature rises.On the outside of LIBs,using the adiabatic condition,reducing the active particles size of the positive and negative electrode materials and choosing suitable porosity are beneficial to improve the performance of LIBs at low temperature.