Modeling crack growth during Li extraction in storage particles using a fracture phase field approach

Storage particles of lithium ion batteries undergo significant mechanical stress during charging and discharging due to the inhomogeneous volume change within the particles when lithium is inserted and extracted. This stress potentially leads to fracture of the particles resulting in detrimental effects for the capacity and internal resistance of a lithium ion battery, such as the growth of additional solid electrolyte interface, loss of contact in conductive pathways or complete disintegration of the electrode. Here, we tackle the problem of fracture in storage particles by merging a coupled model of mechanical stress and diffusion of lithium ions with a phase field description of an evolving crack. This approach allows the simultaneous study of the evolution of the lithium concentration together with the growth of a crack without restrictions to specific geometries, simulation dimensions and presuppositions regarding the crack path. The model was successfully applied to study crack growth during lithium insertion in an earlier work. It was shown that inertia effects play a crucial role with respect to a possible fragmentation of the storage particles. Here, we focus on the opposite charging condition and examine the circumstances under which unstable crack growth and particle breakage can occur during lithium extraction.