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

Abstract

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.