Shielding Fluoride Ion Basicity through Diurea Coordination for Nonaqueous Fluoride Shuttle Batteries

Area of Science:

• Electrochemistry
• Materials Science
• Inorganic Chemistry

Background:

• Fluoride ions (F-) are highly basic, causing electrolyte instability through nucleophilic attacks on organic components.
• This instability limits the development of practical fluoride-ion batteries (FIBs) due to corrosive bifluoride (HF2-) formation.
• Current strategies often involve complex anion acceptors, hindering optimal performance.

Purpose of the Study:

• To enhance the chemical and electrochemical stability of fluoride ion electrolytes.
• To develop a novel coordination strategy for fluoride ions using organic molecules.
• To improve the performance of room-temperature fluoride ion batteries.

Main Methods:

• Replaced water ligands in organic fluoride salts with dual 1,3-diphenylurea (DPU) coordination via hydrogen bonding.
• Investigated the chemical stability of the F-DPU system in various aprotic solvents.
• Evaluated the electrochemical stability window and ionic conductivity of the electrolytes.
• Assessed the (de)fluorination kinetics and battery performance with Pb-PbF2 anodes and BiF3 or Ag cathodes.

Main Results:

• Achieved long-term chemical stability (>1000 hours) in aprotic solvents.
• Broadened the electrochemical stability window to -2.5-0.9 V vs. Ag+/Ag.
• Obtained high ionic conductivity (1.7 mS cm-1) at room temperature.
• Demonstrated faster (de)fluorination kinetics compared to conventional anion acceptor strategies.
• Sustained improved electrochemical performance in room-temperature FIBs.

Conclusions:

• 1,3-diphenylurea coordination effectively suppresses fluoride ion basicity and enhances electrolyte stability.
• The F-DPU system offers a promising alternative for developing high-performance, stable fluoride ion batteries.
• This approach facilitates faster electrode kinetics, paving the way for practical FIB applications.