Hydrofluorocarbon electrolytes for energy-dense and low-temperature batteries

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Traditional electrolyte solvents (oxygen- and nitrogen-based ligands) face limitations in charge transfer at electrode interfaces.
• Dipole-ion interactions, while aiding dissociation, hinder efficient electrochemical reactions.

Purpose of the Study:

• To explore fluorine (F)-based ligands as alternatives to traditional ligands in electrolyte solvents.
• To develop advanced electrolytes for high-energy-density and low-temperature electrochemical devices, particularly lithium-ion batteries.

Main Methods:

• Synthesis of alkanes with monofluorinated structures.
• Formulation of 1,3-difluoro-propane (DFP)-based lithium-ion electrolytes.
• Characterization of electrolyte properties including viscosity, oxidation stability, ionic conductivity, and performance in lithium-metal pouch cells.

Main Results:

• Fluorine-based ligands enable high salt dissolution (>2 mol L⁻¹).
• DFP-based electrolytes exhibit low viscosity (0.95 cP), high oxidation stability (>4.9 V), and excellent ionic conductivity (0.29 mS cm⁻¹ at -70 °C).
• Enhanced lithium plating/stripping with high Coulombic efficiency (up to 99.7%) and exchange current density.
• Lithium-metal pouch cells achieve high energy densities (>700 Wh kg⁻¹ at room temperature, ~400 Wh kg⁻¹ at -50 °C) with minimal electrolyte usage (<0.5 g Ah⁻¹).

Conclusions:

• Designed fluorine-based ligands offer a viable alternative to traditional oxygen- and nitrogen-based ligands in electrolytes.
• Hydrofluorocarbon electrolytes demonstrate significant potential for next-generation energy-dense and low-temperature electrochemical systems.
• This approach overcomes limitations of conventional coordination chemistry in battery electrolytes.