Synergistic Effect between Monodisperse Fe3O4 Nanoparticles and Nitrogen-Doped Carbon Nanosheets to Promote Polysulfide Conversion in Lithium-Sulfur Batteries.

Abstract

Effective fabrication of electrocatalysts active in anchoring and converting lithium polysulfides is critical for the manufacturing of high-performance lithium-sulfur batteries (LSBs). In this study, original Fe3O4 nanospheres with diameters close to 12 nm were finely dispersed over a porous nitrogen-doped carbon matrix by the freeze-drying method to produce a three-dimensional composite material (nano-Fe3O4/PNC) suitable for application as a sulfur host in LSBs. Nano-Fe3O4/PNC loaded with sulfur (S@nano-Fe3O4/PNC) was used as a cathode in a Li-S cell, whose initial discharge specific capacity reached 1256 mA h g-1 at a 0.1 C rate. After 100 charge-discharge cycles at a 0.2 C rate, the reversible capacity of S@nano-Fe3O4/PNC remained at 745 mA h g-1, demonstrating a capacity retention rate of 70%. Importantly, a high Coulombic efficiency of more than 99% was achieved, indicating effective inhibition of the polysulfides' "shuttle effect" by nano-Fe3O4/PNC. The use of electrolytes containing lithium nitrate further reduces the "shuttle effect" of polysulfides. This study demonstrates the synergistic effect between metal oxide nanoparticles and N-doped carbon, which plays an important role in promoting the adsorption and conversion of polysulfides in LSBs.