Towards an Understanding of Li₂ O₂ Evolution in Li-O₂ Batteries: An In Operando Synchrotron X-ray Diffraction Study.

Area of Science:

• Electrochemistry
• Materials Science
• Battery Technology

Background:

• High-performance lithium-oxygen (Li-O₂) batteries face challenges in understanding lithium peroxide (Li₂O₂) behavior during cycling.
• Efficient Li-O₂ battery operation relies on controlling Li₂O₂ formation and decomposition.

Purpose of the Study:

• To investigate the Li₂O₂ formation and decomposition mechanisms in Li-O₂ batteries.
• To elucidate the structural and morphological evolution of Li₂O₂ under electrochemical conditions.

Main Methods:

• Synchrotron radiation powder X-ray diffraction (SR-XRD) was employed to observe Li₂O₂ evolution.
• Quantitative tracking of Li₂O₂ during discharge and charge cycles.

Main Results:

• A two-step process for Li₂O₂ growth and oxidation was identified, linked to distinct mechanisms in oxygen reduction and evolution reactions.
• Disc-like Li₂O₂ grains form rapidly during initial discharge, potentially leading to parasitic reactions.
• Li₂O₂ oxidation during charging occurs first at the surface, followed by bulk delithiation, forming an intermediate.

Conclusions:

• The study provides fundamental insights into the working mechanism of Li-O₂ batteries.
• Understanding the two-step Li₂O₂ evolution is crucial for optimizing Li-O₂ battery performance.
• The findings highlight the role of Li₂O₂ morphology and reaction pathways in battery degradation.