三元活性颗粒在外部载荷作用下锂化诱导断裂的有限离散元分析  

Lithiation⁃Induced Fracture Analysis of Ternary Active Particles Under External Load Based on FDEM

作　　者：张育维 张锴[1] 郑百林[1] ZHANG Yuwei;ZHANG Kai;ZHENG Bailin(School of Aerospace Engineering and Applied Mechanics,Tongji University,Shanghai 200092,China)

机构地区：[1]同济大学航空航天与力学学院,上海200092

出　　处：《力学季刊》2024年第4期993-1005,共13页Chinese Quarterly of Mechanics

基　　金：国家自然科学基金(12372173);上海市自然科学基金(23ZR1468600)。

摘　　要：部分实验发现,对锂离子电池在充放电过程中施加一定外部压力可以提高循环性能,但压力是如何影响活性颗粒的断裂机理仍有待探究.对锂电池施加的外力往往会以两种形式传递到电极颗粒上:一种是通过电池密闭空间中的气体和液体的压缩均匀传递到活性颗粒表面;另外一种是通过电池外壳作用在电极材料上,并通过粘结剂传递到活性颗粒上.本文基于有限离散元(Finite-Discrete Element Method,FDEM)建立了有限变形下的扩散诱导断裂模型,分析三元正极多晶颗粒在嵌锂扩散过程中受外加压力作用时的断裂行为.数值结果表明,对于两类外力传递模型,较小的均布压力都无法将颗粒中心的拉应力降低到不开裂的水平,仍有少量中心裂纹出现;而较大的均布压力使活性颗粒内部的最大主应力变为压应力,对活性颗粒内部结构完整的保持有更好的效果.增加外加压力的大小会使活性颗粒由扩散诱导产生的拉应力全部转化为压应力,避免了拉应力导致的裂纹,抑制了活性颗粒在锂化过程中的裂纹扩展.In some experiments,it was found that applying external pressure to lithium-ion batteries during the charge and discharge process can improve the cycle performance.However,the mechanism of how pressure affects the fracture of active particles remains yet to be explored.The external forces applied to lithium-ion batteries usually transmit to the electrode particles in two ways.One is through the compressed gas and liquid in the sealed space of battery which uniformly transfer the force to the surface of active particles,the other is through the battery casing which transfers the force to the electrode material and then to the active particles via the binder.Based on the Finite-Discrete Element Method(FDEM),this paper presents a diffusion-induced fracture model under finite deformation to analyze the fracture behavior of ternary positive electrode polycrystalline particles under the influence of applied pressure during lithiation.The numerical results indicate that,for both types of force transmissions,even smaller uniformly distributed pressures cannot reduce the tensile stress at the center of the particles to a level that prevents cracking,resulting in the occurrence of a small number of central cracks.In comparison,larger uniformly distributed pressures change the maximum principal stress inside the active particles from tension into compression,thereby better preserving the integrity of the internal structure of the active particles.Moreover,increasing the magnitude of the applied pressure converts all tensile stresses induced by diffusion into compressive stresses,thereby avoiding cracks caused by tensile stress and suppressing the extension of cracks in the active particles during lithiation.

关 键 词：三元多晶颗粒 外加压力 断裂行为 FDEM 

分 类 号：V231.9[航空宇航科学与技术—航空宇航推进理论与工程]