Structural and Thermodynamic Understandings in Mn-Based Sodium Layered Oxides during Anionic Redox

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Anionic redox reactions enable high-energy cathode materials in sodium-ion batteries.
• Oxygen loss during anionic redox causes structural degradation and voltage hysteresis.

Purpose of the Study:

• To develop a stable high-energy cathode material for sodium-ion batteries that utilizes anionic redox.
• To investigate the mechanism behind the stability of a P2-type Mn-based compound.

Main Methods:

• Experimental characterizations (e.g., XRD, TEM, XPS)
• Theoretical calculations (e.g., DFT)
• Electrochemical testing

Main Results:

• A P2-type Mn-based compound demonstrated stable high-potential anionic redox (≈4.2 V) with minimal voltage hysteresis.
• The compound exhibited reversible two-phase behavior involving Na-rich and Na-poor phase unmixing.
• O 2p-electron was confirmed as the origin of the reversible anionic redox reaction.

Conclusions:

• The two-phase reaction mechanism is critical for stabilizing anionic redox in Mn-based layered cathodes.
• Phase separation and lattice mismatch should be considered for rational cathode design.
• This work presents a promising strategy for high-voltage Mn-based layered cathode materials.