Designing Advanced Electrolytes for High-Safety and Long-Lifetime Sodium-Ion Batteries via Anion-Cation Interaction...

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Flammable electrolytes pose significant safety risks in sodium-ion batteries (SIBs).
• Existing nonflammable phosphate electrolytes often require high salt concentrations, limiting compatibility with carbon anodes.
• There is a need for safe, high-performance electrolytes compatible with advanced electrode materials in SIBs.

Purpose of the Study:

• To design and develop low-concentration, nonflammable phosphate electrolytes for enhanced SIB safety and performance.
• To investigate the mechanism of electrolyte stabilization through anion-cation interaction modulation.
• To demonstrate the electrochemical compatibility and long-term stability of the developed electrolyte with hard carbon anodes and NFPP cathodes.

Main Methods:

• Anion-cation interaction modulation strategy using Tris(2,2,2-trifluoroethyl) phosphate (TFEP) as a cosolvent.
• Spectroscopy analyses and theoretical calculations to elucidate electrolyte structure and stabilization mechanisms.
• Fabrication and testing of Ah-level hard carbon (HC)//Na₄Fe_2.91(PO₄)₂(P₂O₇) (NFPP) pouch cells.

Main Results:

• A stable anion-induced ion-solvent-coordinated (AI-ISC) structure was achieved in low-concentration (1.22 M) phosphate electrolytes.
• The developed electrolyte demonstrated excellent compatibility with both HC anodes and NFPP cathodes.
• HC//NFPP pouch cells exhibited high average Coulombic efficiency (>99.9%), excellent capacity retention (84.5% after 2000 cycles), wide operating temperature range (-20 to 60 °C), and passed safety tests.

Conclusions:

• The anion-cation interaction modulation strategy effectively stabilizes low-concentration phosphate electrolytes for SIBs.
• The developed electrolyte offers a promising solution for high-safety, long-lifetime sodium-ion batteries.
• This research provides valuable insights for designing advanced electrolytes for next-generation energy storage systems.