Exploring cycling induced crystallographic change in NMC with X-ray diffraction computed tomography

Area of Science:

• Materials Science
• Electrochemistry
• Crystallography

Background:

• Lithium-ion battery performance relies on electrode material stability during cycling.
• Understanding crystal structure changes at the microscale is crucial for improving battery longevity.
• High-voltage cycling can induce significant stress and degradation in cathode materials.

Purpose of the Study:

• To apply X-ray diffraction computed tomography for analyzing crystal dimension changes in LiNi0.33Mn0.33Co0.33O2 electrodes.
• To spatially map heterogeneities and degradation at the electrode and particle level.
• To correlate electrochemical cycling conditions with changes in unit cell dimensions and material integrity.

Main Methods:

• X-ray diffraction computed tomography (XRD-CT) at 1 μm spatial resolution.
• Electrochemical cycling of LiNi0.33Mn0.33Co0.33O2 electrodes in full cells with graphite anodes.
• Focused ion beam-scanning electron microscopy (FIB-SEM) for cross-section analysis.

Main Results:

• Unit cell volume decreased by 0.4% (4.2 V) and 0.6% (4.7 V) after 100 cycles.
• Extensive particle cracking was observed with increasing upper cut-off voltage.
• XRD-CT detected inhomogeneous lattice parameters within the electrode structure.

Conclusions:

• Electrochemical cycling, especially at higher voltages, induces significant lattice parameter changes and physical degradation (cracking) in LiNi0.33Mn0.33Co0.33O2 electrodes.
• XRD-CT is an effective diagnostic tool for correlating crystal structure evolution with electrochemical performance and identifying localized degradation.
• The technique bridges the gap between crystal structure analysis and battery performance, aiding in the development of more stable electrode materials.