MOF-derived cobalt Disulfide/Nitrogen-doped carbon composite polyhedrons linked with Multi-walled carbon nanotubes as sulfur hosts for Lithium-Sulfur batteries

Abstract

Lithium sulfur batteries (LSBs) are regarded as one of the most promising energy storage devices because of their ultrahigh theoretical energy densities (2500 Wh kg−1), low cost, and environmental friendliness. Nevertheless, several detrimental drawbacks, including shuttling effects caused by soluble lithium polysulfides (LiPS), sluggish conversion kinetics between LiPS, and poor conductivities of sulfur, prevent commercialization of LSBs. To takle the above issues, MOF-derived cobalt disulfide/nitrogen-doped carbon (NC) composite polyhedrons linked with multi-walled carbon nanotubes (MWCNTs), CoS2@NC/MWCNT, were developed as an effective sulfur host for LSBs. It was fabricated through first in-situ growth of nanoporous ZIF-67 on surface treated MWCNTs, followed by carbonization and sulfurization. CoS2@NC/MWCNT combines the advantages of outstanding conductivities of MWCNTs, excellent chemical adsorption of NC and CoS2 toward LiPS, and high catalytic efficiency of CoS2 toward LiPS conversion, effectively addressing the shuttling, sluggish conversion, and low conductivity issues. The CoS2@NC/MWCNT electrode delivered a high specific capacity of 1133 mAh g−1 at 0.1C and maintained a decent specific capacity of 607 mAh g−1 at 2.0C. Its cycling stability is excellent, with a capacity retention rate of 77% after 300cycles at 1.0C, i.e., an average capacity decay rate of 0.078% per cycle. The cycling stability was further improved through increasing N-doping levels of the carbons for enhanced chemical adsorption toward LiPS and through incorporation of inter-linked reduced graphene oxide sheets as a physical barrier to reduce the diffusion loss of LiPS, achieving even smaller capacity decay rates of 0.066 and 0.064 % per cycle, respectively.