Probing Stage Transition Kinetics in Li-Graphite Intercalation Compounds by Time-Resolved In Situ Solid-State NMR via...

Understanding the intrinsic stage-transition kinetics of lithium-graphite intercalation compounds is central to elucidating the electrochemical performance of graphite anodes in Li-ion batteries, yet quantitatively resolving how individual staging phases transform into one another in real time remains experimentally challenging because neighboring staging phases possess closely related structures and compositions, and their transient coexistence is difficult to deconvolute with sufficient temporal resolution. Here, we establish a stage-resolved kinetic metrology based on time-resolved, in situ ¹³C magic-angle-spinning solid-state NMR of ¹³C-enriched graphite, enabling direct, quantitative tracking of the evolution of Li_xC₆ phases during chemically driven delithiation. The large stage-dependent ¹³C chemical-shift dispersion, combined with the >150-fold signal-to-noise enhancement afforded by isotope enrichment, allows minute-scale acquisition and robust spectral deconvolution of coexisting stage-1 (LiC₆), stage-2 (Li_0.5C₆), and dilute-stage (Li_0.33C₆) components. Under quasi-equilibrium oxidative delithiation, staging proceeds predominantly through sequential two-phase transitions, LiC₆ → Li₀.₅C₆ and Li_0.5C₆ → Li_0.33C₆, each well described by Johnson-Mehl-Avrami-Kolmogorov kinetics, consistent with diffusion-limited phase-boundary propagation. This kinetic analysis identifies the dense-stage LiC₆ → Li_0.5C₆ transformation as the intrinsic kinetic bottleneck. When the balance between surface Li removal and intraparticle Li redistribution is perturbed, the staging pathway becomes overlapping and heterogeneous, leading to early emergence of higher-stage phases and extended multiphase coexistence. In these regimes, an effective-order cascade model quantitatively captures the coupled evolution of successive stage transitions. These results reveal how intrinsic stage-transition kinetics and transport constraints jointly govern homogeneous versus heterogeneous delithiation in graphite, and provide a general NMR-based framework for time-resolved quantification of staging transformations in intercalation materials.