Nitrogen and Sulfur Doped Porous Carbon Sheet with Trace Amount of Iron as Efficient Polysulfide Conversion Catalyst for High Loading Lithium-Sulfur Batteries

The major challenges in enhancing the cycle life of lithium-sulfur (Li-S) batteries are polysulfide (PS) shuttling and sluggish reaction kinetics (S to Li2S, Li2S to S). To alleviate the above issues, the use of heteroatom-doped carbon as a cathode host matrix is a low-cost and efficient approach, as it works as a dual-functional framework for PS anchoring as well as an electrocatalyst for faster redox kinetics. Here, the dual role of heteroatom-doped carbon sheets (CS) in the chemisorption of Li2S6 and catalysis of its faster conversion to Li2S is established. To substantiate the catalytic effect, composite cathodes were prepared by encapsulating sulfur in CS which is further blended with carbon nanotubes (CNTs) to form a free-standing cathode. The electrochemical performances of the three cathodes (S@Fe-N-CS-CNT, S@Fe-S-CS-CNT, and S@Fe-NS-CS-CNT) were evaluated by constructing Li-S cells. The S@Fe-NS-CS-CNT delivers a high initial discharge capacity of 1017 mAh g-1 at 0.5 C rate and sustains a capacity of 751 mAh g-1 after 260 cycles with a capacity retention of 73.8 %. Even at a high S loading (12 mg cm-2), it delivers an initial discharge capacity of 892 mAh g-1 and retained 575 mAh g-1 after 200 cycles.