Tuesday, 21 June 2016
Riverside Center (Hyatt Regency)
T. H. Hwang, S. N. Talapaneni, A. Coskun, and J. W. Choi (Korea Advanced Institute of Science and Technology)
Sulfur is one of the most abundant elements and more than 70 million tons of elemental sulfur is annually produced as a by-product of the hydrodesulfurization process in the petroleum refining industry. This mostly involuntary production of sulfur, however, creates a significant global supply surplus. Therefore, the development of highly functional sulfur-rich polymers that are synthesized via direct utilization of elemental sulfur can be a useful direction in recycling the abundant sulfur to high value outcomes. Rechargeable lithium–sulfur (Li-S) batteries have received significant attention in recent years as one of such opportunities owing to their high theoretical gravimetric capacity and energy density of 1,675 mAh g-1 and 2,567 Wh kg-1, respectively. However, despite almost 30 years of development, Li-S batteries are still at the research stage, because of insufficient cycle life mainly due to the fatal redox shuttling process originating from the dissolution of the intermediate lithium polysulfide species in most of operating organic electrolytes during charge/discharge process. Herein, we report, for the first time, sulfur-medidated synthesis of CTF-1 (S-CTF-1) using 1,4-dicyanobenzene and elemental sulfur without any catalysts or solvents. The formation of CTF engages in-situ vulcanization with elemental sulfur, enabling both covalent attachment of sulfur and its homogeneous distribution within the pores. S-CTF-1 was found to have a high sulfur content of 62 wt% along with a well-shaped bipyramidal morphology that has been achieved without using any external template. We have also examined electrochemical performance of S-CTF-1 as a sulfur-cathode material in Li-S batteries. S-CTF-1 exhibited robust cycling performance for 300 cycles with 85.8% capacity retention along with the highest initial Coulombic efficiency (ICE) reported to date: 94.4% at 0.05C (25 mA g-1). Our results demonstrate the promising aspect of microporous polymers as active supports for sulfur, thus it is expected to motivate further research in this area. In a broader perspective, direct utilization of elemental sulfur in the synthesis of covalent triazine frameworks can open up new high-value applications, such as advanced electrode materials for energy storage and conversion.
