Mixed Anionic and Cationic Redox Chemistry in a Tetrathiomolybdate Amorphous Coordination Framework

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Developing advanced electrode materials is crucial for enhancing sodium-ion and lithium-ion battery performance.
• Sulfide materials offer unique electrochemical properties but require further exploration.

Purpose of the Study:

• To investigate the electrochemical properties of a novel sodium molybdate sulfide (Na₂ MoS₄) phase.
• To evaluate its potential as a conversion electrode material for sodium-ion and lithium-ion batteries.

Main Methods:

• Electrochemical characterization of Na₂ MoS₄ in sodium- and lithium-ion cells.
• X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) for material analysis.
• Measurement of electronic conductivity and assessment of redox chemistry.

Main Results:

• Na₂ MoS₄ exhibits an amorphous coordination polymer structure with mixed Mo and S valences.
• The material functions as a mixed ionic-electronic conductor (6.1×10^-4 S cm^-1), enabling carbon-free application.
• A reversible capacity of up to 500 mAh g^-1 was achieved, corresponding to a five-electron redox exchange.

Conclusions:

• Na₂ MoS₄ demonstrates excellent charge-storage performance for both lithium- and sodium-ion batteries.
• This study expands the library of sulfide phases with mixed anionic and cationic redox properties for energy storage.