Phase-field modeling of diffusion-induced crack propagations in electrochemical systems

A three-dimensional phase-field model was developed to simulate and predict crack propagations caused by local variations of solute concentrations. Its application to the electrolyte-LiFePO₄ cathode nanoparticle system in Li-ion batteries captures the Li chemical reaction-intercalation-induced crack propagation during the cell discharging operations. The inherent mechanism underlying the crack propagation is critical for understanding the degradation mechanism limiting battery life and performance. Complex phenomena such as anisotropic coherence strains, elastic inhomogeneity, anisotropic Li diffusion, and chemical reaction of Li ions are fully incorporated in this model. Results of crack propagation in both the bc-plane and ab-plane are consistent with experimental observations. A calculated fracture phase diagram as a function of different nanoparticle sizes and chemical reaction rates provides a failure criterion that is valid for a large class of brittle electrode materials. The current study provides a direct relation between reaction-diffusion-induced stress fields and the observed structural failure in electrochemical system.