Mesoscale heterogeneities in graphite electrodes: Modeling the effect of microstructure and non-ideal anisotropic diffusion on the electrochemical response

Graphite is the state-of-the-art negative electrode material for lithium-ion batteries, valued for its low-cost, high-energy density, and cycling stability. However, it remains important to improve negative electrode performance for fast-charging applications, which has direct implications for optimized electrode microstructures. In this work, we present a three-dimensional microstructural modeling framework that explicitly resolves porous graphite electrodes with stochastic particle arrangements and carbon-binder domains (CBD). The model accounts for particle size distributions, orientation-dependent anisotropic diffusion, and non-ideal solid diffusion to approximate the phase-separating behavior of graphite. Simulations demonstrate that electrode architecture is a critical performance driver: vertically aligned ellipsoids reduce tortuosity and enable higher capacities at elevated C-rates, while random orientations introduce transport limitations. Particle size, contact between particles, and CBD coverage govern lithiation heterogeneities, leading to localized current hotspots and sharp concentration gradients that may accelerate cracking, delamination, and thermal risks. Furthermore, neglecting anisotropy in diffusion models systematically overestimates capacity and underpredicts heterogeneity, especially at intermediate rates. Our developed modeling platform thus provides a high-fidelity description of the interplay between electrode microstructure, anisotropic diffusion, and electrochemical response. Beyond improving predictive accuracy, it offers actionable insights for rational electrode design aimed at enhancing efficiency and mitigating degradation in graphite-based negative electrodes. • 3D microstructural modeling of porous graphite electrodes with carbon-binder-domain • Orientation-dependent anisotropic diffusion in ellipsoidal particles • Non-ideal solid diffusion reveals phase-separation behavior in graphite. • Ignoring anisotropy overestimates capacity.