Structural Distortion-Induced Charge Gradient Distribution of Co Ions in Delithiated LiCoO₂ Cathode

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• Layered lithium cobalt oxide (LiCoO2) is a key cathode material for lithium-ion batteries.
• Structural instability, particularly at high delithiation states, limits LiCoO2 performance.
• Understanding degradation mechanisms is crucial for developing advanced battery materials.

Purpose of the Study:

• To investigate the structural fundamentals of LiCoO2 electrodes at extended delithiation ranges.
• To elucidate the charge compensation mechanisms and their impact on structural stability.
• To identify strategies for enhancing the electrochemical performance and cycle life of LiCoO2 cathodes.

Main Methods:

• In situ and ex situ techniques were employed to study LiCoO2 electrodes.
• Analysis focused on the highly delithiated state to understand charge gradients and structural changes.
• Investigated the role of surface oxygen and lithium-cobalt antisites in charge compensation and stress accommodation.

Main Results:

• A spatial charge gradient of cobalt ions (Co2+/Co3+/Co4+) was observed from the surface to the bulk in highly delithiated LiCoO2.
• Coordinated surface oxygen was found to be electrochemically active and reversible during cycling.
• Introduction of surface lithium-cobalt antisites stabilized active lattice oxygen and accommodated internal stress.

Conclusions:

• The study links structural changes to ion migration kinetics, explaining LiCoO2 degradation during delithiation.
• Stabilizing lattice oxygen and managing internal stress are effective strategies for improving LiCoO2 performance.
• Findings offer insights for developing high energy density cathodes beyond LiCoO2.