Increasing sulfur utilization in lithium-sulfur batteries by a Co-MOF-74@MWCNT interlayer

To improve lithium-sulfur battery performance, Co-MOF-74 has been applied for the first time as an interlayer with multiwalled carbon nanotubes (MWCNTs). Co-MOF-74@MWCNT was synthesized using a solvothermal method. The fabrication of Co-MOF-74@MWCNT was confirmed by scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, and Brunauer-Emmett-Teller testing. The interlayer was fabricated using a filtration method. Assembled batteries were prepared using a Co-MOF-74@MWCNT interlayer and an MWCNT interlayer and subsequently investigated via cyclic voltammetry tests. Co-MOF-74 promotes a redox reaction and shows a small peak at 1.85 V. A symmetric and full cell test revealed that the Co-MOF-74@MWCNT cell enables a faster redox reaction and higher capacity than that of the MWCNT cell. After 15 cycles, the Co-MOF-74@MWCNT cell achieved a value of 1112 mAh g⁻¹, which is 26% greater than that of the MWCNT cell (880 mAh g⁻¹) at 0.2C. Voltage profile testing showed that the reason for the higher capacity of the Co-MOF-74@MWCNT cell is that it promotes the conversion of Li₂S₂ to Li₂S. Various electrochemical analyses confirmed that the Co-MOF-74@MWCNT interlayer acts not only as a physical and chemical barrier but also promotes the transformation of Li₂S₂ to Li₂S.