Dipolar and catalytic effects of an Fe3O4 based nitrogen-doped hollow carbon sphere framework for high performance lithium sulfur batteries

Lithium-sulfur (Li-S) batteries have shown great potential as next generation energy storage systems. However, the practical application is limited by the low electronic/ionic conductivity of sulfur, polysulfide dissolution and sluggish conversion. To solve the above-mentioned problems, a well-designed hollow carbon sphere framework with embedded Fe3O4 nanoparticles (S/Fe3O4-NC) is reported here as an efficient sulfur host for Li-S batteries. In consequence, S/Fe3O4-NC exhibited a high initial discharge capacity of 1264 mA h g(-1) at 0.1 A g(-1), a decent rate performance of 654 mA h g(-1) at 2 A g(-1) and a cycling stability of 61.1% capacity retention after 500 cycles, which are much better than those of a bowl-like hemisphere carbon structure without metal salt (S/NC). The decent performances are not only attributed to physical confinement that prevent polysulfide dissolving. Moreover, we prove that the embedded Fe3O4 nanoparticles can effectively function as polysulfide capture center due to the strong dipolar interactions, so that the polysulfide can largely be fixed and confined in the porous carbon layer. In addition, the high conductivity and catalytic activity of Fe3O4 can accelerate the redox conversion of polysulfide, thus facilitating the reaction kinetics. Benefiting from the structural and chemical optimization, a favorable performance was obtained with a capacity decay of each cycle being only 0.08% for over 500 cycles at 1 A g(-1), showing great potential for practical applications.