Coulombically-stabilized oxygen hole polarons enable fully reversible oxygen redox

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Stabilizing high-valent redox couples and exotic electronic states requires understanding stabilization mechanisms.
• In oxides for energy storage or computing, oxidized anion species rehybridize, causing structural distortions and hysteresis in intercalation electrodes.
• Oxygen redox stabilization is crucial for advanced battery materials.

Purpose of the Study:

• To investigate the mechanism of oxygen redox stabilization in layered Na2-xMn3O7, a positive electrode material with ordered Mn vacancies.
• To elucidate the role of coulombic interactions in stabilizing oxidized oxygen species.
• To understand and mitigate voltage hysteresis in intercalation electrodes.

Main Methods:

• Electrochemical characterization of layered Na2-xMn3O7.
• Analysis of oxygen redox behavior at high potentials (4.2 V vs. Na/Na+).
• Investigation of coulombic interactions between oxidized oxide anions and interlayer Na vacancies.

Main Results:

• Coulombic interactions between oxidized oxide anions and interlayer Na vacancies disfavor rehybridization.
• Hole polarons on oxygen (O-) are stabilized at 4.2 V vs. Na/Na+.
• Coulombic interactions provide significant thermodynamic energy savings, comparable to O-O covalent bonding.
• Achieved ~40 mV voltage hysteresis with negligible fade over multiple cycles.

Conclusions:

• Coulombic interactions are pivotal in stabilizing highly oxidized oxygen species by preventing rehybridization.
• The findings establish a comprehensive understanding of redox energetics, highlighting long-range coulombic effects.
• This work suggests strategies for stabilizing oxidized oxygen in materials for energy storage and other applications.