热失控状态气液两相的锂离子电池建模及修正方法研究

Research on modeling and correction method of gas-liquidtwo-phase lithium-ion battery in thermal runaway state

锂离子电池在应用过程中因滥用而发生热失控现象,导致电池内部产生大量气体,传统的固液两相模型难以准确描述热失控机理。针对以上问题,以18650电池组为研究对象,构建气液两相的锂离子电池模组的电化学-热耦合模型,研究了热失控气体对锂离子电池内部应力、温度、电解液浓度的影响规律,同时利用COMSOL Multiphysics 5.5软件进行了有效性验证和理论模型修正。研究结果表明,锂离子电池热失控气体对电池内部应力、温度、电解液浓度有着明显的正反馈影响规律。内部应力的理论修正值与仿真值峰值均在相近时刻出现,且误差为0.04 MPa,计算精确率提高了80%。电池内部温度到60℃左右时发生热失控,产生的热失控气体在内部温度升高到160℃时被点燃,640 s时达到最高仿真温度,修正温度分别为177、172℃,热失控气体产生的热点现象是影响电池包内部的温度分布不均的主要原因。电解液浓度理论修正值和仿真值从1 200 mol/m3同步下降至837 mol/m3,形成气液两相流,电解液与电极材料反应和分解造成了电解液浓度降低。

Lithium-ion batteries,which are widely used energy storage devices in modern electronic devices and electric vehicles,have been identified as a key component in the transition from depleted fossil fuels to sustainable energy production and use worldwide.However,due to misuse and improper use,lithium-ion batteries can experience thermal runaway,a phenomenon that manifests itself as a significant build-up of gases within the battery.Traditional solid-liquid two-phase models present challenges in characterizing the complexity of thermal runaway mechanisms.In order to understand the mechanism of thermal runaway more accurately,an electrochemical-thermal coupling model of 18650 lithium-ion battery pack is built based on gas-liquid two-phase flow,and the variation law of internal stress,temperature and electrolyte concentration of lithium-ion battery during thermal runaway is well studied.According to the chemical reaction process and the dynamic evolution of internal pressure and temperature,the whole thermal runaway process is divided into reaction stage,diffusion stage and equilibrium stage,so that the characteristics of each stage can be studied in more detail.The effectiveness of the theoretical analysis is verified by using the COMSOL Multiphysics 5.5 software,and the theoretical model is modified,and the results of the comparative analysis show the importance and complementarity of the theoretical analysis and simulation experiments in the study of thermal runaway of lithium-ion batteries.The difference between the peak value of the internal stress correction value and the simulated value is only 0.04 MPa,the error is significantly reduced,and the accuracy is increased by 80%,which indicates that the model can more accurately describe the thermal runaway process of lithium-ion battery,highlighting the accuracy enhancement obtained by this modeling method.Our study also reveals that the thermal runaway gas can cause a drastic change in the internal temperature of the battery,and the amplitude of the change is basically synchronized with the increase of the internal pressure of the battery,the thermal runaway occurs at a temperature of 60℃,and the thermal runaway gas is ignited when the internal temperature rises to 160℃,and the maximum simulated temperature and corrected temperature are 177℃and 172℃at 640 seconds,respectively.The formation of hot spots is the main cause of uneven temperature distribution within the battery.In addition,Our study shows that the electrolyte concentration decreases from 1200 mol/m 3 to 837 mol/m 3 simultaneously from the theoretical and simulated values of the electrolyte concentration caused by the thermal runaway gas throughout the thermal runaway process.This dynamic evolution trend accelerates the formation of gas-liquid two-phase flow and the process of thermal runaway,forming gas-liquid two-phase flow,the interaction between the electrolyte and the electrode material,which leads to the reduction of the electrolyte concentration to a large extent.The electrochemical-thermal coupling model based on gas-liquid two-phase flow and the in-depth study of the thermal runaway process deepens our understanding of the mechanism of thermal runaway of lithium-ion batteries,and provides a more in-depth theoretical basis for preventing or remedying the thermal runaway problem of lithium-ion batteries.