Operando Mapping of Population Phase Separation and Lithium‐Plating Dynamics in Graphite Electrode Using Optical Microscopy and Microstructure Modeling

The fast‐charging capability of phase‐separating graphite electrodes is largely constrained by heterogeneous reaction kinetics and sluggish mass transport at both the particle and electrode scales, which increase the risk of parasitic lithium plating and associated safety concerns. A deeper mechanistic understanding of the interplay among phase‐separation dynamics, electrode microstructure, and lithium‐plating propensity is therefore essential for guiding the rational design of advanced electrode architectures and fast‐charging protocols. Here, we combine operando optical microscopy with three‐dimensional microstructure‐resolved phase‐field modeling to resolve the interplay between phase separation and lithium plating. Microscopy captures stages evolution, phase mode transitions and structural dynamics across the particle population and at the single‐particle level, which is driven by the slow interfacial reactions. Non‐equilibrium phase‐field simulations elucidate the kinetic control mechanisms governing phase transitions as the current varies. Importantly, a new mechanism of lithium plating associated with interfacial ohmic resistance is identified. Based on these insights, we evaluate particle‐size‐distribution design and use thermal activation as a mechanistic probe to resolve how temperature alters phase‐separation pathways and lithium‐plating behavior. These results may serve as a foundation for improving the physical understanding and driving optimization of fast charging protocols for lithium‐ion batteries.