Optimized Nonflammable Concentrated Electrolytes by Introducing a Low-Dielectric Diluent

Area of Science:

• Electrochemistry
• Materials Science
• Battery Technology

Background:

• Concentrated electrolytes using lithium bis(fluorosulfonyl)imide (LiFSA) and trimethyl phosphate (TMP) offer nonflammability and electrode passivation for safer lithium-ion batteries.
• High viscosity and low ionic conductivity of these electrolytes limit their practical application.

Purpose of the Study:

• To address the limitations of concentrated LiFSA/TMP electrolytes by introducing a low-dielectric diluent.
• To investigate the impact of dilution on electrolyte properties, safety, and passivation capabilities.

Main Methods:

• Introduction of 1,1,2,2-tetrafluoroethyl 2,2,3,3,-tetrafluoropropyl ether (HFE) as a diluent into concentrated LiFSA/TMP electrolytes.
• Measurement of viscosity and ionic conductivity.
• Spectroscopic analysis to understand the local coordination state and surface film formation.

Main Results:

• Dilution with HFE significantly reduced electrolyte viscosity to 11.0 mPa s and slightly increased ionic conductivity to 0.87 mS cm⁻¹.
• Nonflammable character and electrode passivation ability were maintained after dilution.
• Spectroscopic analysis revealed a local coordination state similar to the concentrated electrolyte, promoting FSA anion-derived inorganic surface film formation.

Conclusions:

• The addition of HFE effectively improves the performance of LiFSA/TMP electrolytes while retaining their safety features.
• Maintaining a peculiar local coordination state is crucial for designing safe battery electrolytes with enhanced passivation.
• This study highlights a promising strategy for developing advanced electrolytes for safer and longer-lasting lithium-ion batteries.