Abstract
LiNixCoyMn1-x-yO2 (NCM) particles have been used as cathode materials for lithium-ion batteries because of their augmented energy density and elevated operational voltage. However, polycrystalline NCM (PC-NCM) particles exhibit intergranular, intragranular, or hybrid inter/intragranular fractures during electrochemical cycling. In this study, a chemical–mechanical coupling model, an embedded cohesive zone model damage unit, is developed to simulate the fracture evolution of randomly aggregated PC-NCM particles. A damage index is proposed to characterize crack evolution by including the comprehensive influence of crack number, length, and area. The influence of variations in fracture toughness, C-rates, and primary particle size on inter/intragranular fracture evolution is discussed in detail. The coexistent intergranular and intragranular fracture phenomena are successfully simulated and agree well with existing experimental observations. The simulation results indicate that local stress concentration leads to inter- and intra-granular fractures. Increasing the intragranular fracture toughness effectively prevents intragranular fractures but exacerbates intergranular fractures. Higher C-rates worsen intergranular fractures and increase the PC-NCM particle damage value. The effects of the primary particle size on particle damage vary with C-rate and fracture toughness ratio. This study enhances the understanding of the fracture mechanism of PC-NCM particles and offers valuable insights into their design.
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