Ferromagnetic Nanoparticle–Assisted Polysulfide Trapping for Enhanced Lithium–Sulfur Batteries

The lithium–sulfur (Li–S) battery is a promising candidate for next-generation high-density energy storage devices because of its ultrahigh theoretical energy density and the natural abundance of sulfur. However, the practical performance of the sulfur cathode is plagued by fast capacity decay and poor cycle life, both of which can be attributed to the intrinsic dissolution/shuttling of lithium polysulfides. Here, a new built-in magnetic field–enhanced polysulfide trapping mechanism is discovered by introducing ferromagnetic iron/iron carbide (Fe/Fe₃C) nanoparticles with a graphene shell (Fe/Fe₃C/graphene) onto a flexible activated cotton textile (ACT) fiber to prepare the ACT@Fe/Fe₃C/graphene sulfur host. The novel trapping mechanism is demonstrated by significant differences in the diffusion behavior of polysulfides in a custom-designed liquid cell compared to a pure ACT/S cathode. Furthermore, a cell assembled using the ACT@Fe/Fe₃C/S cathode exhibits a high initial discharge capacity of ≈764 mAh g⁻¹, excellent rate performance, and a remarkably long lifespan of 600 cycles using ACT@Fe/Fe₃C/S (whereas only 100 cycles can be achieved using pure ACT/S). The new magnetic field–enhanced trapping mechanism provides not only novel insight but unveils new possibilities for mitigating the “shuttle effect” of polysulfides thereby promoting the practical applications of Li–S batteries.