From Disorder to Staging: Mechanism of Li-ion Diffusion in Graphite Revealed by Large-Scale Molecular Dynamics

Capturing the cross-layer kinetics of intercalants remains a fundamental bottleneck in understanding the structural evolution of layered host materials. This challenge is particularly critical in Li-ion batteries, where designing high-rate graphite anodes is hindered by a lack of mechanistic understanding of intercalation, because theoretical models traditionally address structural order only as out-of-plane staging or in-plane migration. Here, we expanded molecular dynamics simulation dimensions to over 8 nm with 12 graphite layers to fully account for dynamic intra- and interlayer correlations. We observed the collective atomistic evolution at various stages of lithiation, revealing unusual diffusive behavior; for example, upper-layer Li islands regulate the diffusivity of the two underlying layers at stage 3. Furthermore, Li-ion transport becomes highly in-plane anisotropic under the steep concentration gradients characteristic of high-rate operation. By explicitly connecting three-dimensional staging with two-dimensional diffusion, these insights provide the realistic mechanistic baseline necessary for predictive macroscale modeling.