Porous Fe3O4 Nanospheres as Effective Sulfur Hosts for Li-S Batteries

Lithium-sulfur batteries are considered to be one of the most promising candidates for next-generation "beyond lithium-ion" energy-storage systems. However, the commercialization of lithium-sulfur batteries has been hindered by fast capacity fade caused by polysulfide shuttling problems, as well as by a limited volumetric energy density due to low sulfur loading. Here, porous Fe3O4 nanospheres have been employed as a sulfur host to address the polysulfide shuttling problem through chemical interactions. We have employed optical microscopy and cryogenic scanning transmission electron microscopy (cryo-STEM) with X-ray energy dispersive spectroscopy (XEDS) elemental mapping to study the inherent microstructure of an Fe3O4/S composite with 85% sulfur content. We observe well-faceted, micrometer-sized sulfur particles embedded in a network of the conductive Fe3O4 nanosphere host particles. Our Fe3O4/S composite shows high capacity and outstanding cycling stability. The initial areal capacity is 2.6 mAh cm−2 and a high areal capacity of 2.2 mAh cm−2 was retained after 150 cycles. We believe that both the embedding of sulfur, in a conductive Fe3O4 network, and the strong chemical interactions between Fe3O4 and polysulfides are responsible for the high capacity and high cycling stability of our Fe3O4 composite cathode.