A New Class of Oxyhalide Solid Electrolytes NaNbCl_6-2xO_x for Solid-state Sodium Batteries

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Sodium-based batteries offer a cost-effective and abundant alternative to lithium-ion technology.
• Solid-state sodium batteries promise enhanced safety but require advanced electrolytes.
• Current sodium-based solid-state electrolytes (SSEs) lack high ionic conductivity and oxidative stability.

Purpose of the Study:

• To introduce a novel class of sodium-based oxyhalide solid-state electrolytes (SSEs).
• To investigate the synthesis and properties of NaNbCl6-2xOx oxyhalides.
• To evaluate the performance of these electrolytes in solid-state sodium batteries.

Main Methods:

• Facile mechanochemical synthesis of NaNbCl6-2xOx oxyhalides.
• Characterization using 23Na and 93Nb magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy and X-ray diffraction (XRD).
• Fabrication and testing of solid-state sodium batteries with NaNbCl4O electrolyte and a layered cathode.

Main Results:

• The oxyhalide NaNbCl4O demonstrated a ~100-fold increase in ambient-temperature sodium-ion conductivity (1.03×10-4 S cm-1) compared to its halide counterpart.
• Unique structural features related to oxygen incorporation were identified.
• Solid-state sodium batteries achieved a 155 mAh g-1 discharge capacity with good cycle life.

Conclusions:

• The developed NaNbCl6-2xOx oxyhalides represent a promising class of SSEs for sodium-based batteries.
• The enhanced ionic conductivity and stability of NaNbCl4O pave the way for practical solid-state sodium battery applications.
• The successful integration with a cobalt- and nickel-free cathode highlights the potential for sustainable energy storage.