Phase-field modeling of chemo-mechanical relaxation effect on the fracture tolerance of a tin-based electrode

The fracture phenomenon of high-capacity electrode materials during electrochemical cycles poses a major limitation on further advancements in Li-ion batteries. In this paper, a diffusion-creep-stress-fracture coupling model using the phase-field method is established to explore the chemo-mechanical relaxation effect on the fracture tolerance in a tin-based cylindrical electrode during lithiation. The results show that the creep relaxation mechanisms have twofold influence on the evolution of the multi-field system by altering the distribution of stresses. On the one hand, the relaxation mechanism which is crack size-dependent can improve the mechanical stability and fracture resistance of a tin-based electrode; on the other hand, the Li distributions accounting for creep are more uneven than those without creep, which may result in a reduction in usable capacity. Furthermore, the critical state of charge and its improvement for safe state due to creep relaxation are found to be size-dependent with regard to crack size. It can be associated to the stress concentration effect of flaws which can result in the earlier crack propagation and insufficient creep accumulation for a sharper (or longer) crack with large stress concentration.