A 2D Covalent Triazine Framework as an Interconvertible Redox Mediator to Promote Sulfur-Conversion Reactions

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Sluggish sulfur conversion kinetics limit lithium-sulfur (Li-S) battery rate capability and cycling stability.
• Developing efficient redox mediators is crucial for promoting sulfur conversion reactions in Li-S batteries.

Purpose of the Study:

• To synthesize and characterize a crystalline pyrene-4,5,9,10-tetraone functionalized covalent triazine framework (CPTO-CTF) as a redox mediator.
• To investigate the effectiveness of CPTO-CTF in enhancing sulfur conversion kinetics and improving Li-S battery performance.

Main Methods:

• Synthesis of CPTO-CTF with well-defined nanopores and a conjugated framework.
• Electrochemical testing of Li-S batteries utilizing CPTO-CTF as a redox mediator.
• Performance evaluation including discharge capacity, rate capability, and cycling stability.

Main Results:

• CPTO-CTF acts as an interconvertible and rejuvenated redox mediator, promoting sulfur conversion reactions.
• Li-S batteries with CPTO-CTF achieved a high discharge capacity of 1233 mAh g^-1 at 0.2 C.
• Remarkable capacity retention of 95.6% over 600 cycles and high-rate capacity of 604 mAh g^-1 at 5 C were observed.

Conclusions:

• The developed CPTO-CTF effectively promotes sulfur conversion kinetics and utilization of active materials.
• CPTO-CTF demonstrates significant potential for advancing the performance of Li-S batteries.
• The integrated chemical and electrochemical pathway in a prototype pouch cell shows substantial capacity of 810 mAh g^-1 at 0.2 C.