In situ XAFS study on cathode materials for lithium-ion batteries

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Lithium-ion batteries (LIBs) are crucial for energy storage, but capacity fading limits their lifespan.
• Understanding degradation mechanisms in cathode materials like LiNi0.8Co0.2O2 is vital for developing advanced LIBs.
• High-temperature storage and cycling can accelerate battery degradation, necessitating in-depth investigation.

Purpose of the Study:

• To elucidate the electronic and structural changes in LiNi0.8Co0.2O2 during electrochemical cycling and high-temperature storage.
• To correlate these changes with capacity fading observed in LIBs.
• To identify the specific structural distortions responsible for performance loss.

Main Methods:

• In situ X-ray absorption spectroscopy (XAS) at the Ni and Co K-edges was employed.
• Electrochemical cycling and controlled high-temperature storage of LiNi0.8Co0.2O2 coin cells were performed.
• Extended X-ray absorption fine structure (EXAFS) data were quantitatively analyzed.

Main Results:

• Charging the LiNi0.8Co0.2O2 cell caused a shift in Ni and Co K-absorption edges to higher energies.
• A strong correlation was found between the chemical shift range during charging and the cell's capacity.
• Quantitative EXAFS analysis indicated that Jahn-Teller distortion of the NiO6 octahedron is closely related to capacity fading.

Conclusions:

• Jahn-Teller distortion of the NiO6 octahedron is a key factor contributing to capacity fading in LiNi0.8Co0.2O2.
• In situ XAS is a powerful technique for monitoring in-operando structural and electronic changes in battery materials.
• These findings provide critical insights for designing more stable and durable cathode materials for LIBs.