Sulfonated covalent organic framework modified separators suppress the shuttle effect in lithium-sulfur batteries.

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Lithium-sulfur batteries (LSBs) offer high energy density but suffer from poor cycling stability due to the polysulfide shuttle effect.
• The shuttle effect involves soluble polysulfides migrating between electrodes, leading to capacity decay and reduced lifespan.
• Existing separators often fail to mitigate this issue, hindering LSB commercialization.

Purpose of the Study:

• To develop a modified separator that suppresses the polysulfide shuttle effect in LSBs.
• To improve the cycling stability, capacity retention, and overall electrochemical performance of LSBs.
• To investigate the mechanism by which the modified separator enhances ion transport and inhibits polysulfide migration.

Main Methods:

• Fabrication of a sulfonated covalent organic framework (SCOF) modified separator (SCOF-Celgard).
• Electrochemical testing of LSBs using SCOF-Celgard and standard Celgard separators.
• Analysis of capacity retention, cycle life, and rate capability at various current densities.

Main Results:

• The SCOF-Celgard separator effectively inhibited polysulfide shuttling via electrostatic repulsion from sulfonate groups.
• LSBs with SCOF-Celgard showed significantly improved capacity retention (81.1% after 120 cycles at 0.5 C) compared to controls (55.7%).
• Exceptional long-term stability was demonstrated with only 0.067% capacity degradation per cycle after 600 cycles at 1 C, and high capacity at 2 C.

Conclusions:

• SCOF-modified separators are a promising strategy for overcoming the shuttle effect in LSBs.
• The electrostatic repulsion and facilitated Li+ transport mechanisms contribute to enhanced battery performance.
• This approach offers a viable route to improving the practical applicability of high-energy-density lithium-sulfur batteries.