Oxygen Dimerization as a Defect-Driven Process in Bulk LiNiO₂

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Nickel-rich lithium nickel oxide (LiNiO2) is a promising cathode material for lithium-ion batteries.
• High states of charge in these materials can lead to oxygen release and degradation.
• Conflicting reports exist regarding the formation of molecular oxygen within the bulk of LiNiO2.

Purpose of the Study:

• To investigate the potential for oxygen dimerization in the bulk of LiNiO2 cathode materials.
• To understand the role of high charge states in oxygen species formation.
• To elucidate the mechanisms behind bulk degradation in nickel-rich cathodes.

Main Methods:

• Utilized a redox-product structure search methodology.
• Inspired by recent advancements in point-defect structure prediction.
• Focused on delithiated Li1-xNiO2 at x = 1 (fully delithiated state).

Main Results:

• Delithiated LiNiO2 (x = 1) exhibits kinetic stability against decomposition into molecular oxygen.
• Point defects within the material can serve as nucleation sites for oxygen dimerization.
• Defect chemistry plays a crucial role in initiating bulk degradation pathways.

Conclusions:

• Oxygen dimerization can occur in the bulk of LiNiO2, facilitated by defects.
• The findings reconcile previous conflicting observations on oxygen formation in nickel-rich cathodes.
• Understanding defect chemistry is key to mitigating bulk degradation and improving cathode stability.