An Oxychloride Solid Electrolyte with Superior Na-Ion Conductivity

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• All-solid-state sodium batteries (ASSSBs) offer enhanced safety and cost-effectiveness over lithium-ion counterparts.
• Sodium-ion solid electrolytes (SEs) are crucial for ASSSBs but often lag lithium-ion SEs in ionic conductivity.
• Developing high-performance SEs is key to unlocking the potential of sodium-ion battery technology.

Purpose of the Study:

• To synthesize and characterize novel sodium-ion oxychloride solid electrolytes.
• To investigate the ionic conductivity and structural properties of the new SEs.
• To evaluate the performance of these SEs in all-solid-state sodium-iodine batteries.

Main Methods:

• Synthesis of Na-ion oxychloride SEs with the composition Na3xTaO3xCl5-3x using NaTaO3.
• Measurement of room-temperature ionic conductivity and activation energy.
• Characterization using X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS).
• Electrochemical testing of ASSSBs utilizing the developed SE.

Main Results:

• Achieved a high room-temperature ionic conductivity of 2.6 mS cm⁻¹.
• Determined a low activation energy of 0.26 eV for Na+ ion transport.
• Confirmed the oxygen bonding environment and local Na+ coordination via XPS and XAS.
• Demonstrated reversible charge-discharge cycling in all-solid-state sodium-iodine batteries.

Conclusions:

• The novel Na-ion oxychloride SEs exhibit excellent ionic conductivity and low activation energy.
• Synergistic structural features facilitate efficient Na+ migration, crucial for battery performance.
• These materials represent a promising advancement for high-performance and safe all-solid-state sodium batteries.