柱状电极屈曲或裂纹扩展的临界力学参数研究

柱形结构电极是近年来使用最为广泛的锂电池电极结构之一.本文以硅材料细长柱形电极为例,研究了充电电流大小、电极长径比、初始裂纹长度以及断裂韧性对于电极的屈曲现象和裂纹扩展现象发生时间的影响.计算结果表明,屈曲与裂纹扩展现象出现的先后顺序与充电电流大小无关;具有小的长径比,大的初始裂纹长度以及较小断裂韧性的电极,裂纹扩展比屈曲现象更早发生.对于硅材料,不同长径比的电极具有不同临界断裂韧性值,当材料的断裂韧性小于该临界值,在锂化过程中裂纹扩展会先于屈曲现象发生;该临界断裂韧性值随初始裂纹长度的增加而增加.本文的结论对于电极的结构设计以及材料选取具有一定指导意义.

Study on Critical Mechanical Parameters for Buckling or Crack Propagation in Cylindrical Electrodes

The cylindrical electrode is one of the most widely used lithium ion battery electrode structures in recent years. In this paper, the slender cylindrical electrode of silicon was taken as an example to study the effects of charging current, electrode length to diameter ratio, initial crack length and fracture toughness on the onset sequence of buckling and crack propagation of the electrode. The results show that the order of buckling and crack propagation phenomena is independent of the charging current. For electrodes with small length-to-diameter aspect ratio, large initial crack length and small fracture toughness, crack propagation occurs prior to buckling. For silicon materials, electrodes with different length-to-diameter ratios have different critical fracture toughness values. When the fracture toughness of the material is less than the critical value, crack propagation occurs prior to the buckling during the lithiation process. The critical fracture toughness increases with the initial crack length. The conclusions of this paper have certain guiding significance for the structural design and material selection of the electrode.