3D Chemo-Mechanical Simulation of Intergranular Fracture in Polycrystalline Ternary Cathodes Coupled with Damage-Dependent Dynamic Electrolyte Infiltration

Abstract

Polycrystalline ternary cathodes are the dominant high-energy cathode material for commercial lithium-ion batteries, yet intergranular fracture along grain boundaries triggered by lithiation-induced strain severely deteriorates long-term cycling durability. The interconnected grain-boundary crack networks formed during charging provide penetration pathways for liquid electrolyte, creating a bidirectional feedback effect on electrochemical performance: electrolyte infiltration expands electrochemically active surfaces and alleviates kinetic limitations in early cycles, whereas sustained electrolyte-grain boundary interfacial corrosion continuously weakens interfacial mechanical strength and accelerates progressive intergranular crack propagation, forming a self-amplifying degradation loop. Most existing chemo-mechanical numerical simulations for ternary cathodes rely on oversimplified 2D microstructures or artificially predefined fully-wetted crack boundaries, which fail to capture the gradual electrochemical activation of grain-boundary cracks synchronized with dynamic intergranular damage evolution. To fill this research gap, this work establishes a fully coupled 3D finite-discrete element chemo-mechanical framework exclusively equipped with bilinear cohesive zone elements at grain boundaries to characterize intergranular fracture. A novel damage-dependent dynamic electrolyte infiltration model is innovatively proposed to quantitatively correlate local grain-boundary damage magnitude with real-time electrolyte penetration degree and surface electrochemical activity. Systematic 3D parametric simulations are conducted to decouple the individual and synergistic influences of primary particle size and charging C-rate on Li-ion concentration heterogeneity, internal von Mises stress concentration, and cumulative intergranular damage index. Simulation results reveal that intergranular cracking always constitutes the dominant degradation pathway under all tested operating conditions; low charging rates are primarily governed by primary particle size effects, while high C-rates become the decisive factor triggering extensive intergranular crack network proliferation. Compared with the two limiting idealized infiltration scenarios (no infiltration/full instantaneous 100% infiltration), the proposed damage-dependent infiltration model delivers physically realistic intermediate evolution laws for Li distribution, stress accumulation and crack propagation, and explicitly quantifies the bidirectional positive feedback between dynamic electrolyte permeation and intergranular fracture. This 3D modeling framework provides quantitative multi-scale microstructure design guidelines for suppressing grain-boundary cracking and extending the service life of high-energy polycrystalline ternary cathode materials.