Fluoroborate ionic liquids as sodium battery electrolytes

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• High-voltage sodium batteries are crucial for cost-effective energy storage.
• Existing electrolytes face limitations, necessitating safer, high-performance alternatives.

Purpose of the Study:

• To synthesize and evaluate novel ionic liquids (ILs) as electrolytes for high-voltage sodium batteries.
• To identify ILs with improved physical and electrochemical properties for advanced energy storage.

Main Methods:

• Synthesis of six novel ionic liquids based on fluoroborate anions.
• Characterization of physicochemical properties, including glass-transition temperature and viscosity.
• Electrochemical evaluation, including electrochemical window determination and cycling stability tests.
• Investigation of passivation behavior on aluminum current collectors.

Main Results:

• First report of the electrochemically applicable room-temperature ionic liquid (RTIL) [N2(2O2O1)3][B(hfip)4].
• The RTIL exhibits a low glass-transition temperature (-73 °C) and low viscosity.
• An electrochemical window of 5.3 V was achieved, enabling stable sodium cycling.
• Excellent passivation of aluminum current collectors up to 7 V (vs. Na+/Na), enhanced by Na[FSI].

Conclusions:

• Ionic liquids with [B(hfip)4]- anions demonstrate promising properties for high-voltage sodium electrolytes.
• The synthesized RTIL offers a viable alternative to current electrolyte materials.
• These findings support the development of safer and more economical sodium-based energy storage systems.