Porous-crystalline C/Fe3O4 microspheres with highly accessible adsorptive/catalytic and conductive interfaces to manipulate polysulfide shuttling in Li-S batteries

We used different C/Fe3O4 microspheres such as dense-amorphous and porous-crystalline, prepared by spray pyrolysis with steam oxidation, to clarify the synergetic effect of conductive and adsorptive/catalytic interfaces on the electrochemical properties of Li-S batteries. According to the physical characterizations, the prepared C/Fe3O4 microspheres significantly differ in their surface texture, porosity, and crystal structures. The porous-crystalline C/Fe3O4 microspheres have a wide range of micro-and mesopores to physically adsorb polysulfides and highly accessible Fe3O4 nanoparticles to chemically immobilize them within the electrochemical interfaces and promote their conversion into short-chain sulfides. On the other hand, a densely coated carbon of the dense-amorphous C/Fe3O4 microspheres impedes the chemical interaction between the polysulfides and Fe3O4 nanoparticles. As a result, the porous-crystalline C/Fe3O4 microspheres enhance sulfur utilization and accelerate the redox kinetics of Li–S cells when used as modified separators. These cells exhibit a higher specific capacity of ⁓700 mAh g–1 with a capacity retention of 93% after 200 cycles at 1.0 C. This work demonstrates that high-performance Li–S batteries can be achieved by rationally designing conductive and adsorptive/catalytic interfaces of C/Fe3O4 microspheres.