Fluorinated amorphous halides with improved ionic conduction and stability for all-solid-state sodium-ion batteries

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Developing solid electrolytes is crucial for safer and more efficient all-solid-state sodium-ion batteries.
• Existing sodium-based halide electrolytes often suffer from low ionic conductivity and poor stability.
• Understanding structure-property relationships is key to optimizing ion transport.

Purpose of the Study:

• To design sodium halide solid electrolytes with significantly improved ionic conductivity and electrochemical stability.
• To establish a facile method for tuning vacancy and charge carrier concentrations in sodium halides.
• To enhance the performance and cyclability of all-solid-state sodium-ion batteries.

Main Methods:

• A facile Na- and Cl-deficient composition method was employed to regulate vacancy and charge carrier concentrations.
• Fluorination-induced amorphization was used to improve electrochemical stability and interfacial compatibility.
• Electrochemical performance was evaluated using specific electrode materials (Na3V2(PO4)3 and Na15Sn4) and the developed catholyte (Na0.5ZrCl4F0.5).

Main Results:

• The Na- and Cl-deficient method resulted in a several-fold enhancement in ionic conductivity of sodium halides.
• Fluorination-induced amorphization improved stability without compromising conductivity, attributed to increased local disorder and prismatic Na coordination.
• The Na0.5ZrCl4F0.5 catholyte enabled a battery to operate for 300 cycles with 94.4% capacity retention at room temperature.

Conclusions:

• The developed strategy offers a versatile pathway for creating high-performance inorganic ion conductors.
• This research advances the development of all-solid-state sodium-ion batteries with high conductivity and long-term cyclability.
• Optimizing composition and structure is critical for achieving superior ionic conductivity and stability in solid electrolytes.