Phase-Field Modeling of Single Crystallization of NCM613 Cathodes
Single-Crystal (SC) layered oxides have been extensively studied as NCM cathode materials due to the enhanced mechanical durability, resistance to intergranular cracking, and improved interfacial stability with electrolyte. The difficulty in scaling up SC-LiNi 0.6 Co 0.1 Mn 0.3 O 2 (mid-nickel SC-NCM) synthesis stems from a lack of fundamental knowledge in understanding the phase transformation mechanism during high-temperature calcination and sintering process. Herein, we examine the single crystallization mechanism using a phase-field method to understand densification and grain growth during the high temperature process. The phase-field method employed allows for multiple simultaneous processes including diffusion along surface/grain boundary/bulk lattice, vapor transport, particle rigid body motions of translation and rotation, and grain growth through boundary migration. We find that the oxygen partial pressure plays an important role in governing grain growth kinetics. Specifically, the stabilization of grain boundaries under high oxygen partial pressure prevents localized coalescence, thereby ensuring a homogeneous microstructure despite lowering the sintering kinetics. In contrast, low-oxygen partial pressure facilitates rapid single-crystal growth by promoting diffusion, significantly reducing the time required for the sintering process. These findings elucidate the underlying mechanisms behind the experimental time-efficient sintering kinetics, offering a clear understanding of the balance between structural stability and processing time.