A sodium superionic chloride electrolyte driven by paddle wheel mechanism for solid state batteries.

Area of Science:

• Materials Science
• Solid-State Chemistry
• Electrochemistry

Background:

• Halide materials are attractive solid electrolytes for energy storage applications due to their high ionic conductivity and oxidation stability.
• Developing novel halide solid electrolytes with superior performance is critical for advancing battery technology.

Purpose of the Study:

• To investigate the superionic properties of NaTaCl₆ as a solid electrolyte.
• To elucidate the relationship between anion dynamics and ionic conductivity in halide materials.
• To compare the performance of NaTaCl₆ with NaNbCl₆ for potential use in solid-state batteries.

Main Methods:

• Synthesis and characterization of NaTaCl₆ and NaNbCl₆.
• Ionic conductivity measurements at room temperature.
• Analysis of polyanion rotational dynamics using techniques sensitive to molecular motion.
• Electrochemical stability window determination.
• Solid-state cell fabrication and cycling performance evaluation.

Main Results:

• NaTaCl₆ exhibits a high ionic conductivity of 3.3 mS cm^-1 at 27 °C, two orders of magnitude higher than NaNbCl₆ (0.01 mS cm^-1).
• The superior conductivity of NaTaCl₆ is attributed to more facile rotational dynamics of the [TaCl₆] polyanions compared to [NbCl₆] anions.
• Enhanced anion rotation in NaTaCl₆, linked to structural disorder and phonon softness, directly facilitates Na⁺ ion diffusion.
• NaTaCl₆ demonstrates good rate capability and long-term cycling stability in solid-state cells due to its ionic conductivity and electrochemical stability.

Conclusions:

• NaTaCl₆ is a promising superionic halide solid electrolyte with significantly enhanced ionic conductivity.
• The rotational dynamics of polyanions play a critical role in governing ion transport in halide solid electrolytes.
• This study provides fundamental insights into the ion transport mechanisms in emerging halide solid electrolytes, paving the way for their application in next-generation solid-state batteries.