The mechanical instability of solid electrolyte interphase (SEI) layer during the lithiation and delithiation cycles in lithium-ion batteries (LIBs) is partly but importantly responsible for capacity fade and high cell impedance in the batteries. In this study, the SEI’s fracture and failure processes are deeply investigated using traditional fracture mechanics methods. Particularly, a derived traction-separation law of a two-phase SEI species from an atomistic calculation is used to study damage accumulation and failure within the grains and along the boundaries of grains in the SEI. Crack initiation and propagation mode in porous SEI and bulk grains are studied using an extended finite element method (XFEM) based on diffusion-stress analyses, and the stress level thresholds for crack initiation in the components are determined. The results also show that maximum stresses occur at the surface of the anode particles in the normal direction and hence, subjecting the SEI to Mode-I loading. The quantitative analysis on the crack evolution provides a thorough understanding of the failure mechanism on the SEI layer and can be utilized in optimizing and controlling the SEI-related parameters.

Keywords: SEI, Traction-separation, Crack, Fracture