Microstructural Adjusting Crack Evolution of Polycrystalline NCM Particle during Charge/Discharge Cycle

The occurrence of cracks inside LiNi _x Co _y Mn _1-x-y O ₂ (NCM) polycrystalline particles induced by charge/discharge limits their applications. In this study, a chemomechanical damage model was established to obtain insight into the crack characterization of NCM secondary particles induced by the charge/discharge processes. Two key factors (the primary particle sizes and regularities) that govern the microstructures, were included in the geometrical model established using the Voronoi algorithm. Cohesive elements were inserted into the primary particle edges to perform a comprehensive simulation of interparticle cracks. Different crack characterizations in cycle processes were disclosed through a discussion of stress, crack evolution and morphology, and damage degree. The primary particle size and regularity have significant effects on both the crack morphology and damage degree. Tensile stress contributes the most to charge-induced cracks, whereas both tensile and shear stresses are the main contributors to discharge-induced cracks. The accumulation of deformation energy plays a vital role in the discharge process. The discharge process causes more damage than the charge process under high fracture energies, but this can be transferred when the fracture energy decreases. The phenomena and mechanisms offer a comprehensive understanding of the charge/discharge-induced degradation in NCM secondary particles and can guide the rational design of microstructures.