Raman spectroscopy complemented with XRD and TEM for studying structural evolution in initial cycles of...

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• Nickel-manganese-cobalt (NMC) cathode materials are crucial for high-energy lithium-ion batteries.
• Understanding structural evolution during cycling is key to improving battery longevity and performance.

Purpose of the Study:

• Investigate the structural changes in NMC111 cathode material during extended potential window cycling.
• Identify mechanisms responsible for capacity fading and performance loss in high-voltage lithium-ion batteries.

Main Methods:

• Utilized in situ and ex situ Raman spectroscopy for real-time and post-mortem analysis.
• Employed ex situ X-ray diffraction (XRD) for bulk structural evolution.
• Conducted high-resolution transmission electron microscopy (HR-TEM) to observe microstructural changes.

Main Results:

• Observed energy-dependent Raman response linked to electronic band structure and phase transitions.
• Identified reversible surface layer reconstruction to a cubic phase at high potentials, leading to irreversible degradation.
• Detected bulk structural changes, significant volume variations, and stress accumulation causing particle cracking via XRD and TEM.

Conclusions:

• Integrated characterization reveals complementary surface and bulk modifications in NMC111.
• Surface reconstruction and bulk stress accumulation are primary drivers of capacity fading and cracking.
• Findings are essential for designing improved high-voltage NMC cathode materials for enhanced battery performance.