Quantifying Reaction and Rate Heterogeneity in Battery Electrodes in 3D through Operando X-ray Diffraction Computed...

Area of Science:

• Materials Science
• Electrochemistry
• Chemical Engineering

Background:

• Composite battery electrodes exhibit nonuniform energy storage reactions due to local ionic and electronic transport limitations.
• Understanding this reaction heterogeneity is crucial for optimizing battery performance, rate capability, and mitigating degradation.
• Heterogeneity impacts battery lifespan and overall efficiency.

Purpose of the Study:

• To spatially map and quantify reaction heterogeneity in a composite electrode during battery cycling.
• To identify the specific transport limitations (ionic and electronic) contributing to reaction nonuniformity.
• To provide data for validating and improving multiscale battery models.

Main Methods:

• Utilized spatially resolved X-ray diffraction computed tomography (XRD-CT) to visualize reaction progression.
• Investigated a composite electrode utilizing lithium iron phosphate (LiFePO4) as the active material.
• Performed charge and discharge cycles to observe dynamic reaction behavior.

Main Results:

• Observed accelerated reactions at electrode faces, indicating limitations from both ionic and electronic transport.
• Quantified significant variability in charge/discharge rates across the electrode architecture over time.
• Determined that local reaction rates can be 2-5 times higher than the average rate.

Conclusions:

• Electrode reaction heterogeneity, driven by transport limitations, significantly influences battery performance and degradation.
• The observed rate variations have critical implications for understanding and optimizing rate-dependent battery behavior.
• The study provides a benchmark for multiscale continuum models, enabling their application to diverse electrode designs.