A bifunctional interlayer fabricated by FeS2-embedded N-doped carbon nanocages with efficient polysulfide trapping-catalyzing capability for robust Li-S batteries

Shuttling behavior and sluggish redox kinetics of lithium polysulfides (LiPSs) are fundamental reasons that impede the practical application of lithium-sulfur batteries (LSBs). Herein, a novel FeS2-embedded N-doped carbon (FeS2-NC) nanocage is reported as a separator coating material to alleviate these problems. It is also for the first time that FeS2 is applied to the separator coating of LSBs. The yolk-pleat-shell structure of FeS2-NC was synthesized via the pyrolysis of iron complexes prepared by Schiff base condensation and subsequent sulfurization treatment. The large internal space of FeS2-NC not only physically confines LiPSs but also forms a high-speed electron–ion transport network in cooperation with the highly polar compound FeS2, providing abundant chemical adsorption and catalytic sites for fast conversions of LiPSs. Theoretical calculation further confirms that FeS2 has strong adsorption energy for both Li2S6 and Li2S8, while in-situ Raman analysis also reveals the interaction between FeS2 and LiPSs. In addition, coin cells with the light functional separator (coating loading: 0.2 mg cm−2) have a ultrahigh initial capacity of 1613.6 mAh g−1 at 0.1C and a satisfactory cyclability of 652.3 mAh g−1 at 1C over 600 cycles with an attenuation rate of 0.049% per cycle. Even the high-sulfur-loaded (2.73 mg cm−2) pouch cell release a lasting high areal capacity of 2.38 mAh cm−2 at 0.4C. These results demonstrate that FeS2-NC has the efficient capability as polysulfide trapping-catalyzing nanoreactor for LSBs application.