Chemical-state distributions in charged LiCoO₂ cathode particles visualized by soft X-ray spectromicroscopy

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• Lithium-ion battery cathode performance relies on lithium deintercalation/intercalation reactions within individual particles.
• Understanding local chemical state changes in cathode materials is key to improving battery energy density and cycle life.

Purpose of the Study:

• To spatially resolve chemical state distributions in LiCoO2 cathode particles during charging.
• To investigate the role of cobalt and oxygen sites in charge compensation mechanisms.
• To identify inhomogeneous reaction patterns and non-active regions within cathode particles.

Main Methods:

• Utilized scanning transmission X-ray microscopy (STXM) for high-resolution imaging of LiCoO2 particles.
• Employed X-ray absorption spectroscopy (XAS) at Co L3- and O K-edges to probe electronic structure.
• Performed element mapping derived from STXM stack images to visualize spatial distribution of elements.

Main Results:

• STXM-STXM and XAS revealed distinct spatial distributions of chemical states in LiCoO2 particles at different charging levels.
• Changes in both Co and O K-edge XAS spectra indicate participation of both sites in charge compensation, likely via Co 3d-O 2p hybridization.
• Element mapping demonstrated inhomogeneous reaction distributions within active particles and identified non-active particles.

Conclusions:

• Spatially resolved electronic structure analysis using STXM is effective for understanding battery material charging/discharging.
• Inhomogeneous reactions within individual cathode particles significantly impact overall battery performance.
• The findings highlight the importance of particle-level analysis for optimizing layered cathode materials.