基于电化学-热耦合模型研究隔膜孔隙结构对锂离子电池性能的影响机制

隔膜孔隙结构对锂离子电池性能具有重要的影响,本文提出了可准确描述充放电过程中锂离子电池内部复杂物理化学现象的电化学-热耦合模型,发现该模型较文献中模型的计算结果更接近实验测试数据.利用该模型探讨了隔膜孔隙率与扭曲率分别对锂离子电池性能的影响规律,发现减小孔隙率或增大扭曲率,电池输出电压、最大放电容量和平均输出功率均不断降低,电池表面温度和温升速度均不断升高;当孔隙率减小或扭曲率增大到一定程度时,放电初期电池输出电压均会出现先下降后回升的现象,且孔隙率越小或扭曲率越大,其下降的幅度越大、速度越快,回升所需时间也越长;要确保其不低于截止电压,隔膜扭曲率必须小于临界扭曲率(其下降至最低点刚好等于截止电压时的隔膜扭曲率).综合分析了放电过程中电池内部各电化学参量和产热量的动态分布规律,发现隔膜孔隙率和扭曲率主要影响放电末期电极膜片内部电化学反应以及其他放电时刻电解液中有效Li~+扩散(传导)系数.

Mechanism of influence of separator microstructure on performance of lithium-ion battery based on electrochemical-thermal coupling model

Separator is an important component of lithium-ion battery,and the microstructure of separator has an important influence on the performance of lithium-ion battery.In the present paper,an electrochemical-thermal full coupling model is developed to accurately describe the complex physicalchemical phenomena in lithium-ion battery in charge and discharge process.The simulation results by the present model are closer to the experimental results than those by the previously published model.What is more,the present model is widely used to investigate the effects of the separator porosity and tortuosity on the performance of lithium-ion battery,respectively.The simulation results show that with separator porosity decreasing or separator tortuosity increasing,the output voltage,maximum discharge capacity and average output power of lithium-ion battery decrease,and the lithium-ion battery surface temperature and its rising rate increase.In the initial stage of discharge,when the separator porosity decreases or separator tortuosity increases to a certain degree,the output voltage of lithium-ion battery first decreases and then increases.The smaller the separator porosity or the higher the separator tortuosity,the larger the range and rate of reducing the output voltage of lithium-ion battery become and the longer the rise time needs in the initial stage of discharge.To ensure that the output voltage of lithium-ion battery is higher than the cut-off voltage,the separator tortuosity must be less than the critical tortuosity (It is equal to the separator tortuosity of the lithium-ion battery with the lowest output voltage,which is just equal to the cut-off voltage in the initial stage of discharge).Finally,a comprehensive analysis is conducted on the dynamic distribution of the electrochemical parameters and various heat productions in lithium-ion battery during charge and discharge.It can be clearly found that the electrochemical reactions in the end of discharge,the diffusion coefficients and the conduction coefficients of Li⁺ of electrolyte in the initial and middle stage of discharge are mainly influenced by the separator porosity and tortuosity.The research results in the present paper not only provide theoretical and technical support for the separator microstructure design and optimization,but also has important realistic meanings for improving or perfecting the preparation technology of the separator.