Decoding chemo-mechanical degradation: A unified phase-field model for intergranular fracture in aggregated Ni-rich cathodes

Ion movement in solid-state materials can cause lattice strain. The chemo-mechanical degradation of aggregated cathode materials, particularly LiNi_xCo_yMn_zO₂ (NCM), remains a critical bottleneck limiting the lifespan and safety of high-energy lithium-ion batteries. This degradation is dominated by intergranular cracking, driven by heterogeneous stresses originating from anisotropic Li⁺ diffusion and lattice strain within randomly oriented primary particles. However, predicting this complex, microstructure-dependent failure pathway remains a significant challenge. Here, a high-fidelity, multi-physics phase-field damage model is developed to unify the coupled electrochemical-mechanical behavior governing NCM aggregates. Crucially, the model is informed by realistic microstructures obtained from Focused Ion Beam (FIB) tomography and integrates anisotropic lattice strains derived from X-ray Diffraction (XRD) data. This framework effectively simulates damage accumulation and crack evolution during Li⁺ diffusion. Simulations reveal that radially oriented primary grains mitigate anisotropic stress and subsequent damage. Furthermore, a local sensitivity analysis identifies Poisson's ratio as the most dominant mechanical parameter governing stress localization and potential failure. This work provides a robust predictive tool for understanding mechanical failure at the aggregate scale, offering rational design principles for developing next-generation, crack-tolerant cathode materials.