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

The sluggish sulfur conversion kinetics have significantly restricted the rate capability and cycling stability of lithium-sulfur (Li-S) batteries. To address this issue, a crystalline pyrene-4, 5, 9, 10-tetraone functionalized covalent triazine framework (CPTO-CTF) is developed, incorporating well-defined nanopores, a fully conjugated framework with abundant redox-active moieties, which can act as an interconvertible and rejuvenated redox mediator to promote sulfur-conversion reactions. The invertible chemical oxidation/reduction between PTO/lithiated PTO and sulfur species can facilitate the conversion reactions and lead to a high utilization of active materials. As a consequence, the CPTO-CTF@S battery delivers high discharge capacity of 1233 mAh g^-1 at 0.2 C, high-rate capacity of 604 mAh g^-1 at 5 C, and remarkable retention of 95.6% over 600 cycles. The integrated chemical- and electrochemical-pathway further demonstrates its effectiveness in a prototype pouch cell, which delivers a substantial capacity of 810 mAh g^-1 at 0.2 C.