A Honeycomb-Structured CoF₂-Modified Separator Enabling High-Performance Lithium-Sulfur Batteries.

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Lithium-sulfur (Li-S) batteries face challenges due to poor electronic conductivity and the shuttle effect of lithium polysulfides.
• These issues severely limit the development of Li-S batteries with high sulfur loading, hindering practical applications.

Purpose of the Study:

• To introduce a honeycomb-structured cobalt difluoride (CoF2)@carbon composite as a functional separator layer.
• To enhance lithium-ion transport, catalytic activity, and suppress the shuttle effect in Li-S batteries.

Main Methods:

• Fabrication of a honeycomb-structured CoF2@C composite.
• Adhesion of the CoF2@C composite as a functional layer to the separator.
• Electrochemical testing of Li-S cells with the modified separator under various conditions (sulfur loading, cycling rates).

Main Results:

• The CoF2-modified separator demonstrated excellent cycle stability with a low capacity decay of 0.076% per cycle over 300 cycles at 1 C (2.0 mg cm-2 sulfur loading).
• A capacity decay of 0.088% per cycle for 200 cycles at 0.2 C was achieved with a higher sulfur loading of 3.0 mg cm-2.
• High capacity retention of 697.5 mA g-1 was obtained at a sulfur loading of 4.0 mg cm-2 with an electrolyte/sulfur ratio of 8 μL mg-1.

Conclusions:

• The CoF2@C functional layer effectively addresses key limitations in Li-S batteries, including poor conductivity and polysulfide shuttle.
• The modified separator enables rapid ion transport and high catalytic activity, leading to superior electrochemical performance.
• This approach shows significant promise for advancing practical Li-S battery technology with high energy density and long cycle life.