Break it down to speed it up: Na₂O-NaTaCl₆.

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Fast sodium-ion conductors are crucial for developing safe and cost-effective all-solid-state sodium batteries.
• Current challenges include achieving high ion transport rates necessary for high-power density applications.

Purpose of the Study:

• To synthesize a novel sodium solid electrolyte, Na₂O-NaTaCl₆ (Na₂O-NTC), using an energy-efficient approach.
• To investigate its ionic conductivity and structural properties for potential use in solid-state sodium batteries.

Main Methods:

• Mechanochemical milling of Na₂O and NaTaCl₆ for 4 hours.
• Characterization using X-ray diffraction (XRD), Raman spectroscopy, and high-resolution Nuclear Magnetic Resonance (NMR).
• Measurement of ionic and electronic conductivity.

Main Results:

• Achieved a high ionic conductivity of 4.41 mS cm⁻¹ and low activation energy of 0.32 eV for Na₂O-NTC.
• The conductivity of Na₂O-NTC was over ten times higher than crystalline NaTaCl₆ (NTC).
• Na₂O acted as a glass modifier, amorphizing NaTaCl₆ into a glassy oxyhalide with fast Na⁺ dynamics and low electronic conductivity (6.72 × 10⁻¹⁰ S cm⁻¹).

Conclusions:

• Inexpensive glass modifiers can transform low-conductivity crystalline materials into highly conductive glassy solid electrolytes.
• The energy-efficient synthesis of Na₂O-NTC demonstrates a viable route to advanced glassy superionic conductors.
• This facilitates the development of high-performance rechargeable solid-state sodium batteries.