Roadblocks in Cation Diffusion Pathways: Implications of Phase Boundaries for Li-Ion Diffusivity in an Intercalation...

Area of Science:

• Materials Science
• Electrochemistry
• Solid-state Chemistry

Background:

• Lithium-ion intercalation into host materials can induce structural transformations.
• These transformations, involving dislocations and stress gradients, are linked to capacity fading in batteries.
• The impact of these phase transformations on lithium-ion diffusivity is not well understood.

Purpose of the Study:

• To investigate the structural origins of evolving lithium-ion diffusivities in layered V2O5 during electrochemical lithiation.
• To correlate changes in lithium-ion diffusivity with phase progression and structural features.

Main Methods:

• Galvanostatic intermittent titration (GIT) to measure lithium-ion diffusivity.
• Raman spectroscopy and X-ray diffraction (XRD) for phase identification.
• First-principles density functional theory (DFT) calculations for migration barriers.
• Scanning transmission X-ray microscopy (STXM) for single-particle phase domain imaging.

Main Results:

• Lithium-ion diffusivity in V2O5 varied by over 4 orders of magnitude with lithiation.
• Dips in diffusivity correlated with phase mixtures; monophasic regimes showed highest diffusivity.
• DFT calculations indicated comparable intrinsic migration barriers across different lithiated V2O5 phases.
• STXM revealed distinct domains of coexisting lithiated phases within individual particles.

Conclusions:

• Phase boundaries formed during lithiation, not intrinsic diffusion pathways, are responsible for significant ion transport penalties.
• Interfacial phenomena and phase inhomogeneities profoundly impact macroscopic electrode properties.
• Understanding these structural origins is crucial for designing high-performance intercalation hosts for batteries.