Sulfur enriched carbon nanotubols with a Poly(3,4-ethylenedioxypyrrole) coating as cathodes for long-lasting Li-S batteries

Abstract

Lithium-sulfur (Li-S) batteries are technologically significant for sulfur is cheap, and offers high gravimetric capacity and a large energy density. But achieving long term cyclability with moderate capacity loss, and scalability pose formidable challenges. A solution phase approach for the preparation of a composite of sulfur with hydroxyl groups functionalized multiwalled carbon nanotubes (MWCNTols) and coated with poly(3,4-ethylenedioxypyrrole) (PEDOP) is presented for the first time. Comparison of the Li-S performances at 0.1 C current-rate show that the S based cell with a S-loading of 80% retains a low capacity of 122 mAh gsulfur−1 after 100 cycles, whereas cells with S/MWCNTols and S/MWCNTols/PEDOP composites with sulfur loadings of 73 and 70% respectively, retain capacities of 384 and 624 mAh gsulfur−1 after 200 charge-discharge cycles, with Coulombic efficiencies of 96 and 98.7% respectively. This performance differential illustrates the role of PEDOP in inhibiting sulfur loss and in maximizing cell response. The polymer provides electrical interconnects between the insulating sulfur clusters and facilitates Li+ transfer at the interface. The ease of the synthesis, coupled with the remarkable cycling performance delivered by this composite at a high sulfur-loading, demonstrate the promise that this S/CNT/conducting polymer composite has for practical Li-S batteries.