Origin of Reversible Interlayer-Disorder-Induced Phase Transitions in Layered Sodium Manganese Oxide Cathodes

Area of Science:

• Materials Science
• Electrochemistry
• Computational Chemistry

Background:

• Reversible phase transitions in sodium birnessite (Na_xMnO₂·yH₂O) are crucial for high-performance layered oxide cathodes.
• The microscopic origin of these transitions and their contradiction with conventional computational predictions remain unclear.

Purpose of the Study:

• To resolve the discrepancy between experimental observations and theoretical predictions of phase transitions in sodium birnessite.
• To elucidate the role of potential-driven charge effects on the thermodynamics and kinetics of phase transitions.

Main Methods:

• Utilized a novel charge-dependent computational framework incorporating potential-driven charge effects.
• Analyzed the regulation of interlayer species-MnO₂ interactions and structural responses.

Main Results:

• Demonstrated that charge effects fundamentally alter the layered-to-spinel transition landscape.
• Showed the spinel-like phase becomes thermodynamically favored at high desodiation and elevated potentials.
• Identified a significantly reduced transition barrier (0.19 eV) under operating conditions, explaining experimental reversibility.

Conclusions:

• Resolved the longstanding puzzle of sodium birnessite phase transitions.
• Provided fundamental insights into potential-driven charge effects in layered oxide cathodes.
• Highlighted the importance of charge effects for designing next-generation alkali-metal-ion batteries.