动力锂电池三元正极低温性能研究

Characteristics of ternary cathode of lithium-ion power battery at low temperature

动力锂离子电池低温下放电性能衰减问题一直是制约新能源电动汽车在寒冷地区推广应用的瓶颈。研究表明,动力锂离子电池正极性能对其低温放电性能产生主要的影响。因此,全面系统地了解正极低温特性具有十分重要的意义。本文以商用动力锂电池三元正极为研究对象,设计在25℃、0℃、-10℃和-35℃温度下的电池测试实验,建立从电池、极片到正极材料在低温下性能演变的关联性研究,揭示三元正极体系在低温下的性能变化特征。实验结果表明,低温对三元动力锂电池的放电容量和内阻有显著影响。随着温度的降低,电池极化内阻增大趋势远超欧姆内阻。三元正极在低温测试后表现出面密度下降、电导率下降、碳含量增加、晶胞收缩、活性损失以及颗粒开裂的特征,阻碍了电子和锂离子的迁移,引起电化学动力学参数恶化,导致电化学性能衰减。本文对揭示三元正极低温特征,帮助技术人员开发高质量低温性能动力锂电池,提升电动汽车在严寒地区推广运行方面具有一定的作用。

The low-temperature discharge performance of lithium-ion power battery affects the promotion and application of electric vehicles(EVs)in cold regions.The characteristic performances of the cathode have a major influence on the low-temperature performances of lithium-ion batteries;therefore,it is crucial to systematically understand the low-temperature characteristics of the cathode.Herein,the charge and discharge test experiments of commercial ternary lithium-ion power batteries are performed at 25℃,0℃,-10℃and-35℃.Furthermore,the characteristics of the ternary cathode system are revealed by studying the performance evolution of battery,cathode,and ternary material at different low temperatures.The experimental results reveal that the low temperature has a considerable effect on the discharge capacity and internal resistance of the batteries.At low temperatures,the polarization internal resistance increases faster than the ohmic resistance.With the decrease in testing temperature,the ternary cathodes show the characteristics of decreasing surface density,decreasing conductivity,increasing carbon content,shrinking of cells,loss of activity,and particle cracking.These changes in ternary cathodes hinder the migration of electrons and lithium ions,cause the deterioration of electrochemical kinetic parameters and lead to the attenuation of electrochemical performance.Thus,this study reveals the low-temperature characteristics of ternary cathode,which will help technicians in developing high-performance low-temperature power batteries and improve the promotion of EVs in cold regions.