Optimized Electrode/Electrolyte Interface of MWCNT/SnO₂ Composite through Gas-Solid Fluorination.

Area of Science:

• Materials Science
• Electrochemistry
• Surface Chemistry

Background:

• Fluorine enrichment of the solid-electrolyte interface is crucial for secondary lithium-ion batteries.
• Surface fluorination of electrode materials offers an alternative strategy for fluorine incorporation.
• Selective fluorination of SnO2 in MWCNT/SnO2 composites is essential.

Purpose of the Study:

• To investigate two surface fluorination methods (F2(g) and XeF2(s)) on MWCNT/SnO2 composites.
• To analyze the impact of different fluorination depths and resulting layers on battery performance.
• To demonstrate the benefits of surface fluorine addition for electrode stability.

Main Methods:

• Surface fluorination of MWCNT/SnO2 composites using gaseous fluorine (F2(g)).
• Surface fluorination of MWCNT/SnO2 composites using solid xenon difluoride (XeF2(s)).
• Electrochemical testing to evaluate gravimetric capacities and cycle stability.

Main Results:

• F2(g) treatment resulted in an ultrathin, dense fluorinated layer, yielding stable capacities of 789 mA h g-1 after 50 cycles.
• XeF2(s) treatment created a thin, porous layer and a novel Sn-based fluorinated phase, also stabilizing capacities.
• Both methods confirmed the positive effect of surface fluorine on electrode cycle stability.

Conclusions:

• Surface fluorination of MWCNT/SnO2 composites effectively enhances electrochemical performance.
• The nature of the fluorinated layer (dense vs. porous) influences the resulting interface and performance.
• Fluorine incorporation via surface modification is a viable strategy for improving battery anode stability.