Nanosize Cation-Disordered Rocksalt Oxides: Na₂ TiO₃ -NaMnO₂ Binary System.

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Development of rechargeable sodium batteries requires novel positive electrode materials utilizing earth-abundant elements.
• Increasing theoretical capacity necessitates higher sodium content in host structures, leading to the exploration of sodium-excess compounds.

Purpose of the Study:

• To synthesize and evaluate novel sodium-excess compounds in the Na2TiO3-NaMnO2 binary system as potential positive electrode materials for rechargeable sodium batteries.
• To investigate the electrochemical performance and redox mechanisms of these new materials.

Main Methods:

• Synthesis of sodium-excess compounds with a cation disordered rocksalt structure was achieved using a mechanical milling method.
• Electrochemical performance was evaluated, and redox reactions were confirmed using X-ray absorption spectroscopy.

Main Results:

• A novel material, Na1.14Mn0.57Ti0.29O2, was successfully synthesized and demonstrated a large reversible capacity of approximately 200 mA h g-1.
• Reversible cationic (Mn3+/Mn4+) and anionic (O2-/On-) redox reactions were identified as the source of the high capacity.
• The study confirmed that holes in oxygen 2p orbitals are stabilized by electron donation from Mn ions, enhancing electrochemical oxidation.

Conclusions:

• The synthesized Na-excess compound, Na1.14Mn0.57Ti0.29O2, shows significant potential as a high-capacity positive electrode material for rechargeable sodium batteries.
• The reversibility of anionic redox was notably improved compared to previous studies.
• This research contributes to the development of sustainable energy storage solutions using abundant elements.