Development of vanadium-based polyanion positive electrode active materials for high-voltage sodium-based batteries

Area of Science:

• Materials Science
• Electrochemistry
• Inorganic Chemistry

Background:

• Polyanion compounds are promising for sodium-ion battery electrode materials due to their diverse structures.
• Developing high-capacity and high-voltage cathode materials is crucial for advancing sodium-ion battery technology.

Purpose of the Study:

• To synthesize and characterize a novel polyanion compound as a positive electrode active material for sodium-ion storage.
• To evaluate the electrochemical performance of the developed material in a sodium-ion coin cell.

Main Methods:

• Low-temperature ion-exchange synthesis (190°C) to combine NaVPO4F and a KTiOPO4-type framework.
• Coin cell testing with a sodium metal anode and NaPF6-based electrolyte.
• Ex situ and operando structural characterizations to elucidate the storage mechanism.

Main Results:

• The synthesized material achieved a discharge capacity of 136 mAh g⁻¹ at 14.3 mA g⁻¹ with an average voltage of 4.0 V.
• A specific discharge capacity of 123 mAh g⁻¹ at 5.7 A g⁻¹ was also observed.
• Reversible sodium-ion storage was confirmed to occur primarily through a solid-solution de/insertion mechanism.

Conclusions:

• A novel, high-performance cathode material for sodium-ion batteries was successfully developed.
• The material exhibits excellent capacity and voltage, suitable for practical applications.
• Understanding the solid-solution mechanism provides insights for future material design.