Depth-to-Areal Staging Heterogeneity Preceding Lithium Plating in Graphite Anodes Revealed by Operando Imaging

Lithiation in graphite electrodes proceeds heterogeneously, yet how this heterogeneity develops in space, and how it responds to the kinetic conditions of charging, remains poorly resolved because conventional probes report only volume-averaged behavior. Here we resolve how graphite staging heterogeneity evolves across both the through-thickness and in-plane directions of the electrode, and how its severity is governed by charging kinetics. Combining operando optical microscopy, in situ x-ray diffraction, color-space analysis, and electrode-scale simulation, we track lithiation from the particle scale to the full electrode as a function of electrode porosity and charging rate. Lower porosity and higher rate intensify tortuosity-controlled Li⁺ transport limitation, generating through-thickness lithiation gradients that evolve into pronounced in-plane staging non-uniformity, such that neighboring regions advance through the staging sequence at markedly different rates. Critically, operando imaging directly reveals that domains reaching advanced lithiation states earliest become the preferential sites at which lithium plating initiates, demonstrating that plating is spatially templated by pre-existing staging heterogeneity rather than nucleating randomly. These findings establish staging heterogeneity as a kinetically controlled precursor to plating and provide a general operando framework for diagnosing heterogeneity-driven behaviour in insertion electrodes.