Fe3C/Fe nanoparticles embedded in N-doped porous carbon nanosheets and graphene: A thin functional interlayer for PP separator to boost performance of Li-S batteries

The sluggish conversion and severe shuttle effect of soluble polysulfides in lithium-sulfur (Li-S) cells are still the urgent problems for boosting their practical application, although they have been considered as one of the most promising candidates for the advanced energy storage devices in the near future. Herein, a heterostructural Fe3C/Fe@NC/G nanocomposite, in which the Fe3C and Fe nanoparticles are well-embedded in the N-doped porous carbon nanosheets and graphene substrate, is firstly prepared by a novel two-steps temperaturecontrolled calcination, and then it is used to modify the conventional PP separator. The thin Fe3C/Fe@NC/G coating layer can not only effectively block the diffusion of dissolved polysulfides through the physical barrier and chemical binding, but also accelerates the redox conversion of polysulfides as a functional catalyst. As a result, a Li-S cell prepared by this modified separator and a S/KB composite with a high sulfur content of 70 wt% in the final cathode displays high discharge capacity and good cycling capability, with a high specific capacity of - 1489 mAh g-1 at 0.1C and a capacity decline rate of - 0.062% per cycle during 500 cycles at 1.0C, respectively. Furthermore, this functional separator can enable a Li-S cell with a high sulfur areal loading of 5.0 mg cm-2 to perform well, with a high specific capacity of 618 mAh g-1 at 0.1C and a good cycling stability. This facile and effective strategy will provide better insight to develop high-energy Li-S batteries, from the perspective of improvement of kinetics conversion and decrease of shuttle effect of the polysulfides simultaneously.