Surface Fluorination of Reactive Battery Anode Materials for Enhanced Stability

Area of Science:

• Materials Science
• Electrochemistry
• Chemical Engineering

Background:

• High-capacity anodes such as lithium metal and lithiated silicon are crucial for increasing battery energy density.
• These reactive anode materials suffer from environmental corrosion and electrolyte incompatibility, hindering their practical application.
• Developing a robust protective layer is essential for their stability during handling and cycling.

Purpose of the Study:

• To develop a facile and safe surface fluorination method for creating a protective coating on reactive anode materials.
• To evaluate the effectiveness of the LiF coating in enhancing the electrochemical performance and stability of lithium metal and lithiated silicon anodes.
• To demonstrate the compatibility of the coated materials with standard battery fabrication processes.

Main Methods:

• A surface fluorination process using CYTOP as a precursor to generate in situ fluorine gas for LiF coating formation.
• Electrochemical cycling of lithium metal anodes with LiF coating in carbonate electrolytes.
• Processing and electrochemical evaluation of lithiated silicon anodes with LiF coating in N-methyl-2-pyrrolidinone (NMP) and stability testing in humid air.

Main Results:

• The LiF coating on lithium metal anodes suppressed dendrite formation and corrosion, enabling stable cycling for over 300 cycles at 5 mA/cm².
• Lithiated silicon anodes coated with LiF demonstrated a high capacity of 2504 mAh/g and were processable in anhydrous NMP.
• The LiF coating provided stability to lithiated silicon in humid air (∼40% relative humidity).

Conclusions:

• The developed surface fluorination process offers a safe and effective method for creating a stable LiF interphase on high-capacity anodes.
• This LiF coating significantly improves the cycling stability and processability of lithium metal and lithiated silicon, benefiting both current lithium-ion and future battery technologies.
• The protective LiF layer addresses key challenges in the practical implementation of advanced anode materials for high-energy-density batteries.