Porous Dithiine-Linked Covalent Organic Framework as a Dynamic Platform for Covalent Polysulfide Anchoring in Lithium–Sulfur Battery Cathodes

Abstract

Dithiine linkage formation via a dynamic and self-correcting nucleophilic aromatic substitution reaction enables the de novo synthesis of a porous thianthrene-based two-dimensional covalent organic framework (COF). For the first time, this organo-sulfur moiety is integrated as a structural building block into a crystalline layered COF. The structure of the new material deviates from the typical planar interlayer π-stacking of the COF to form undulated layers caused by bending along the C–S–C bridge, without loss of aromaticity and crystallinity of the overall COF structure. Comprehensive experimental and theoretical investigations of the COF and a model compound, featuring the thianthrene moiety, suggest partial delocalization of sulfur lone pair electrons over the aromatic backbone of the COF decreasing the band gap and promoting redox activity. Postsynthetic sulfurization allows for direct covalent attachment of polysulfides to the carbon backbone of the framework to afford a molecular-designed cathode material for lithium–sulfur (Li–S) batteries with a minimized polysulfide shuttle. The fabricated coin cell delivers nearly 77% of the initial capacity even after 500 charge–discharge cycles at 500 mA/g current density. This novel sulfur linkage in COF chemistry is an ideal structural motif for designing model materials for studying advanced electrode materials for Li–S batteries on a molecular level.

The Properties, Synthesis, and Materials Applications of 1,4-Dithiins and Thianthrenes

“…62 Very recently, Haldar et al expanded upon this methodology with the synthesis and characterization of DUT-177 (102), which was found to be both highly porous (S BET = 709 m 2 /g) and crystalline in nature (Figure 3). 103 This crystallinity enabled a more thorough investigation into the structure of the polymer, providing evidence for the formation of honeycomb-type pores. Subsequent sulfurization of the polymer network resulted in a highly stable cathode material for a Li-sulfur battery, demonstrating 77% capacity retention after 500 cycles.…”

“…Subsequent sulfurization of the polymer network resulted in a highly stable cathode material for a Li-sulfur battery, demonstrating 77% capacity retention after 500 cycles. 103…”

Catalytic Effects of Electrodes and Electrolytes in Metal–Sulfur Batteries: Progress and Prospective

“…Porous network S-COP-99 1287.7 mAh g -1 at 0.05 C 243.1 mAh g -1 at 5 C 1.0 m LiTFSI in 1:1 DOL and DME with 0.2 m LiNO 3 [31] DUT-177 -S-DUT-177 720 mAh g -1 at 0.1A g -1 276 mAh g -1 at 1 A g -1 LiTFSI in 1:1 DOL and DME with 0.1 m LiNO 3 [32] RT Na-S batteries Atomic Co Cluster S@Co n -HC 820 mAh g -1 at 0.1 A g -1 220 mAh g -1 at 5 A g -1 1.0 m NaClO 4 in propylene carbonate (PC)/ethylene carbonate (EC) + 5 wt% fluoroethylene carbonate (FEC)),…”

Industry-compatible covalent organic frameworks for green chemical engineering

“…COFs are suitable for LSBs due to accessible cavities and electronic interactions between the layers in 2D COFs. Kaskel's group [139] presented a thianthrene-based COF (DUT-177) (Figure 10b) with a high specific capacity of 700 mA h/g sulfur at 100 mA/g sulfur . Chen et al [140] reported triazine-based COFs (COF-Tr-BA), which exhibited specific discharge capacities of 1,400, 948, 841, 767, and 714 mAh/g, respectively.…”