AFM as an analysis tool for high-capacity sulfur cathodes for Li-S batteries

Area of Science:

• Materials Science
• Electrochemistry
• Battery Technology

Background:

• Lithium-sulfur (Li-S) batteries offer high theoretical energy density but suffer from capacity fading.
• Cathode stability and maintaining electrical conductivity are critical challenges for Li-S battery performance.

Purpose of the Study:

• To analyze the nanoscale electrical, electrochemical, and morphological properties of Li-S battery cathodes.
• To compare cathode performance based on preparation methods (suspension-spraying vs. doctor-blade coating) and binders.
• To identify key factors influencing cathode stability and battery cycling performance.

Main Methods:

• Material-sensitive atomic force microscopy (AFM) techniques for nanoscale analysis.
• Scanning electron microscopy (SEM) for morphological studies.
• Conductive AFM and conductive tapping mode AFM for electrical property assessment.
• X-ray diffraction (XRD) for material characterization.

Main Results:

• Spray-coated cathodes with polyvinylidene fluoride (PVDF) binder demonstrated superior morphological and electrical network stability.
• A reduction in conductive area, measured by conductive AFM, correlated with battery capacity loss.
• Insulating lithium sulfide (Li2S) hydrolysis to insulating lithium hydroxide (LiOH) was confirmed by XRD, highlighting the importance of post-cycling analysis.
• Optimized cathode design led to improved discharge capacity (800 mA·g(sulfur)(-1) after 43 cycles).

Conclusions:

• Spray-coating with PVDF binder enhances the stability of Li-S battery cathodes.
• Preserving the conductive network throughout cycling is crucial for sustained battery capacity.
• AFM is a valuable tool for understanding degradation mechanisms and optimizing Li-S battery cathode design.