Simulation of intergranular fracture behavior inside randomly aggregated LiNixCoyMn1-x-yO2 polycrystalline particle

Abstract

The degradation of secondary particles caused by intergranular fracture is an important reason for the capacity fading of LiNixCoyMn1-x-yO2 (NCM) polycrystalline electrodes. In this study, a chemomechanical damage model was established to implement a simulation of fracture behavior under different fracture energies, interfacial strengths and C-rates. Cohesive elements were applied along the interfaces of randomly distributed primary particles, generated by the Voronoi algorithm to simulate their separation during lithiation. The damage dissipation energy was calculated to characterize the propagation of cracks. The simulation results showed that the fracture energy and strength between primary particles play an important role in the intergranular fracture behavior. Increasing the C-rates brings two different aggravating effects to the fracture of secondary particles in different cycle stages. The extensive propagation of the main crack suppresses the growth of secondary cracks under a high C-rate or small fracture energy. Island particles and holes that appeared in many experiments after a long-term cycling protocol were simulated for the first time. The evolution of the simulated cracks was consistent with many published experimental images. The method and results are of great significance for understanding the fracture behavior of NCM cathodes.