Fluorinated Zr-MOF-modified separators for Li-S batteries with enhanced electrochemical performance

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Demand for new energy solutions drives research into advanced battery technologies.
• Lithium-sulfur (Li-S) batteries offer high theoretical energy density but suffer from polysulfide shuttle effects.
• Metal-organic frameworks (MOFs) are explored as separator modifications to improve battery performance.

Purpose of the Study:

• To synthesize and evaluate Zr-based MOFs (UiO-66-4F and UiO-66) for modifying lithium-sulfur battery separators.
• To investigate the impact of fluorine substitution in MOFs on the electrochemical performance of Li-S batteries.
• To assess the ability of fluorine to mitigate the polysulfide shuttle effect.

Main Methods:

• Solvothermal synthesis of UiO-66-4F and UiO-66 using ZrCl4, H2BDC-4F, and H2BDC.
• Coating of synthesized MOFs onto commercial Celgard separators.
• Electrochemical testing of assembled Li-S batteries, including cycling performance and capacity retention at various current densities and sulfur loadings.

Main Results:

• UiO-66-4F modified separators exhibited superior electrochemical performance compared to UiO-66.
• At 0.5C, the UiO-66-4F cell achieved an initial discharge capacity of 1182.9 mAh g⁻¹ and retained 400.7 mAh g⁻¹ after 1000 cycles.
• Even with high sulfur loading (4 mg cm⁻²), the UiO-66-4F cell maintained a high reversible capacity of 961.28 mAh g⁻¹.
• UiO-66-4F demonstrated better cycling stability and lower capacity decay rates.

Conclusions:

• The electron-withdrawing fluorine group in UiO-66-4F effectively inhibits the polysulfide shuttle effect.
• Fluorinated MOF modification significantly improves the cycling performance and capacity retention of Li-S batteries.
• UiO-66-4F presents a promising strategy for enhancing the practical application of Li-S battery technology.