Heat Transfer Fluids as Co-Diluents in Localized High-Concentration Electrolytes for High-Rate Lithium Metal...

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Localized high-concentration electrolytes (LHCEs) show promise for lithium metal batteries (LMBs) due to effective interphase formation.
• However, reduced ion transport kinetics hinder the practical application of LHCEs in LMBs.

Purpose of the Study:

• To identify novel co-diluents for LHCEs to improve ion mobility and battery performance.
• To enhance the safety and electrochemical stability of electrolyte formulations for LMBs.

Main Methods:

• Screening of industrially established fluorinated ethers as co-diluents.
• Formulation of ternary co-diluent electrolyte blends.
• Electrochemical characterization including cycling, overpotential, and Coulombic efficiency measurements.
• Ex situ analysis of electrode morphology and interphase composition.

Main Results:

• Two fluorinated ethers were identified as effective co-diluents, offering a wide electrochemical stability window, low viscosity, and non-flammability.
• The ternary co-diluent formulation demonstrated enhanced ion mobility by reducing viscosity and limiting ion clustering.
• Improved high-rate performance with lower overvoltages and higher Coulombic efficiencies (≥1 mA cm⁻²).
• Markedly extended cycle life in application-oriented zero-excess pouch cells compared to baseline.

Conclusions:

• Fluorinated ethers serve as safe and effective co-diluents for LHCEs, improving ion transport kinetics.
• Enhanced ion mobility, not interphase modification, is the primary driver for improved high-rate performance in these advanced electrolytes.
• This approach offers a viable strategy for developing safer, high-performance electrolytes for lithium metal batteries.