Bio-based ether solvent and ionic liquid electrolyte for sustainable sodium-air batteries

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Sodium-air batteries (SABs) offer high theoretical energy density but rely on flammable and toxic organic solvents like diglyme.
• Safety concerns limit the practical application of current SAB technologies.
• Developing safer electrolyte alternatives is crucial for next-generation batteries.

Purpose of the Study:

• To investigate 1,2,3-trimethoxypropane (TMP) as a branched ether solvent alternative to diglyme in SABs.
• To address the reactivity of TMP with sodium metal and improve electrolyte stability.
• To enhance SAB performance and safety through electrolyte formulation and anode protection.

Main Methods:

• Electrochemical testing of SABs with TMP-based electrolytes.
• Utilizing a Na-β-alumina disk for sodium anode protection.
• Characterization of discharge products using SEM, Raman, and 23Na NMR spectroscopy.
• Investigating the effect of N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([C4mpyr][TFSI]) as a co-solvent.

Main Results:

• Identified reactivity of TMP's tertiary carbon with sodium metal, mitigated by [C4mpyr][TFSI] co-solvent.
• Achieved improved discharge capacities of up to 1.92 mA h cm-2 (TMP) and 2.31 mA h cm-2 (TMP/[C4mpyr][TFSI]).
• Confirmed NaO2 cubes as the major discharge product and observed reduced side-product formation with the hybrid electrolyte (ratio 2.4 vs 0.8).

Conclusions:

• TMP shows significant potential as a safer, base solvent for sodium-air batteries.
• Electrolyte composition design, including co-solvents, is critical for optimizing SAB performance and safety.
• This research contributes to the development of greener and less toxic energy storage solutions.