A High-Voltage Membrane-Free Li-Organic Hybrid Flow Battery Using Eutectic Lithium Chemistry

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Membrane-free redox flow batteries offer design simplicity and cost reduction but face performance limitations.
• Developing high-voltage, stable, and efficient nonaqueous flow batteries is crucial for advanced energy storage.

Purpose of the Study:

• To construct and evaluate a high-voltage, membrane-free Li-organic hybrid flow battery utilizing a biphasic electrolyte system.
• To demonstrate the feasibility of eutectic lithium chemistry and immiscible solvent interfaces for improved flow battery performance.

Main Methods:

• Fabrication of a biphasic electrolyte system with a deep eutectic solvent anolyte (lithium hexafluorophosphate and 2,2,2-trifluoroacetamide) and a dichloromethane catholyte.
• Incorporation of a phenothiazine derivative in the catholyte for redox reversibility and phase confinement.
• Electrochemical characterization including cycling stability, Coulombic efficiency, and self-discharge analysis.

Main Results:

• The deep eutectic solvent anolyte exhibited a wide electrochemical stability window (4.81 V), low viscosity, high ionic conductivity, and lithium metal compatibility.
• The biphasic system achieved an open-circuit voltage of ~3.6 V, retained 85.6% capacity over 100 cycles, and showed minimal self-discharge in flow configuration.
• The battery demonstrated strong flame resistance and a preliminary cost of $134.8 kWh⁻¹, lower than vanadium redox flow batteries.

Conclusions:

• The developed membrane-free nonaqueous Li-organic hybrid flow battery offers a promising, cost-effective, and safe energy storage solution.
• The biphasic electrolyte strategy effectively addresses performance limitations of traditional membrane-free flow batteries.
• This work provides a viable design for future high-performance, low-cost flow battery systems.