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

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State NMR Spectroscopy

Background:

• Understanding lithium-graphite intercalation kinetics is vital for Li-ion battery anode performance.
• Quantifying real-time phase transitions in intercalation compounds is experimentally challenging due to structural similarities and transient coexistence.

Purpose of the Study:

• To establish a stage-resolved kinetic metrology for tracking LiₓC₆ phase evolution during delithiation.
• To quantitatively analyze the intrinsic stage-transition kinetics of lithium-graphite intercalation compounds.

Main Methods:

• Utilized time-resolved, in situ ¹³C magic-angle-spinning solid-state NMR on ¹³C-enriched graphite.
• Employed isotope enrichment for enhanced signal-to-noise (>150-fold) enabling minute-scale acquisitions.
• Applied spectral deconvolution to resolve coexisting stage-1, stage-2, and dilute-stage LiₓC₆ phases.

Main Results:

• Demonstrated sequential two-phase transitions (LiC₆ → Li₀.₅C₆ and Li₀.₅C₆ → Li₀.₃₃C₆) under quasi-equilibrium delithiation, following Johnson-Mehl-Avrami-Kolmogorov kinetics.
• Identified the LiC₆ → Li₀.₅C₆ transformation as the intrinsic kinetic bottleneck.
• Showcased that perturbed Li removal/redistribution leads to heterogeneous staging pathways and extended multiphase coexistence, captured by an effective-order cascade model.

Conclusions:

• Intrinsic stage-transition kinetics and transport constraints jointly govern homogeneous versus heterogeneous delithiation in graphite anodes.
• Provided a general NMR-based framework for time-resolved quantification of staging transformations in intercalation materials.
• The developed metrology offers direct insights into electrochemical performance limitations of graphite anodes.