3D phase-field modeling of H2→H3 phase transition induced intragranular cracking in single-crystal Ni-rich layered cathodes

Understanding the intragranular cracking mechanisms of single-crystal Ni-rich layered cathodes (SC-NCM) during electrochemical cycling is essential for next-generation high-energy-density and long-life Li-ion batteries. However, the complex interplay among the factors driving crack initiation and propagation remains unclear. Herein, we present a fully coupled three-dimensional phase-field model that integrates anisotropic lithium diffusion, the H2-H3 structural phase transition, stress evolution, and fracture mechanics to elucidate intragranular fracture in SC-NCM during deep delithiation. Simulations on representative particle geometries reveal that anisotropic diffusion and fracture energy alone can not initiate layer-parallel cracks, instead, layered delithiation pathways govern shape-dependent phase transition dynamics, while lattice mismatch from spatially heterogeneous phase transitions nucleates cracks preferentially at particle surfaces and drives their propagation along layered planes, in good agreement with experimental observations. Cubic particles with uniform layers form cracks prematurely, whereas spherical and octahedral particles—with shorter surface layers—delay crack initiation by 5.3% state of charge (SoC) due to retarded phase transition in central layers, thereby expanding the safe-charging window. Elevated charging rates accelerate central-layer phase transition, amplifying misfit and triggering earlier cracking, while reduced phase-transition eigenstrain or flatter aspect ratios mitigate stress concentrations and suppress damage. These results establish a predictive link between phase transition dynamics and intragranular fracture, providing design strategies for mechanically robust high-energy-density cathodes.