Insertion of fluorine into a LiFePO₄ electrode material by gas-solid fluorination

Area of Science:

• Materials Science
• Inorganic Chemistry
• Electrochemistry

Background:

• Lithium iron phosphate (LiFePO4) is a key cathode material for lithium-ion batteries.
• Fluorination is explored to enhance material properties and stability.

Purpose of the Study:

• Investigate the effects of molecular fluorine (F2) fluorination on LiFePO4 at varying temperatures.
• Develop a novel method for synthesizing stable fluorinated compounds, including LiFePO4F.

Main Methods:

• Fluorination of LiFePO4 using F2 gas at different temperatures.
• Post-fluorination thermal treatment under nitrogen (N2).
• Characterization using X-ray diffraction, Raman, infrared, Mössbauer spectroscopy, 7Li NMR, and electrochemical methods.

Main Results:

• Low-temperature fluorination results in core delithiation and LiF shell formation.
• High-temperature fluorination leads to decomposition into iron fluorides (α-FeF3 and α-Li3FeF6).
• A subsequent N2 treatment yields the novel LiFePO4F compound.

Conclusions:

• Fluorination temperature critically controls the reaction pathway and product formation in LiFePO4.
• A new route to synthesize LiFePO4F was established.
• The method shows potential for synthesizing other fluorinated materials, such as NaFePO4.