Hierarchical hybrid architecture of carbon nanotube branches grown onto steam activated-reduced graphene oxide/Ni nanoparticle for lithium-sulfur battery cathode

Hierarchically structured carbon architecture is considered as a promising candidate of lithium-sulfur battery cathodes owing to its large surface area and percolated electron/ion pathways. However, the synthesis of hierarchical carbonaceous materials requires complicated processes and the resulting materials usually provide weak physical interactions to capture lithium polysulfides, which significantly hinders the performance of lithium-sulfur batteries. In order to resolve these problems, we have demonstrated a facile microwave-assisted synthesis of carbon nanotubes branches grown onto steam-activated reduced graphene oxide (sGNC) to simultaneously synthesize hierarchical carbon structure and nickel nanoparticles for the inhibition of lithium polysulfides shuttle. The hierarchical structure of carbon nanotubes branched from anchored nickel nanoparticle seeds, and uniform distribution of sulfur is attributed to the facilitated electron/ion diffusion pathway, sufficient space to impregnate sulfur, and the lithium polysulfides capturing sites. Accordingly, sGNC-sulfur (sGNC-S) cathode achieved the initial discharge capacity of 829.3 mAh g - 1 at 0.5 C, which is much higher than 531.8 mAh g - 1 of steam-activated reduced graphene oxide-sulfur (sG-S) cathode. When the current rates increased from 0.1 C to 1 C, the capacity retention of the sGNC-S cathode was 67.0%, greater than 62.5% of the sG-S cathode. The decay rate of 0.155%/cycle with the Coulombic efficiency of almost 100% over 200 cycles of the sGNC-S cathode was greater than 0.219%/cycle of the sG-S cathode, originating from facile kinetics and restricted polysulfide dissolution.

Automated summary

Hierarchically structured carbon architecture with large surface area and percolated electron/ion pathways shows promise as a cathode material for lithium-sulfur batteries. However, the synthesis of hierarchical carbonaceous materials is complicated and they often have weak interactions with lithium polysulfides, limiting battery performance. A microwave-assisted synthesis method was used to create carbon nanotubes grown onto steam-activated reduced graphene oxide (sGNC), resulting in a hierarchical carbon structure and nickel nanoparticles that inhibit lithium polysulfides. The sGNC-S cathode exhibited higher initial discharge capacity, better capacity retention, and lower decay rate compared to the sG-S cathode.