Controlled Construction of Cobalt-Doped Carbon Nanofiber–Carbon Nanotubes as a Freestanding Interlayer for Advanced Lithium–Sulfur Batteries

The major challenges for the realistic application of lithium-sulfur batteries (LSBs) lie in the great difficulties in breaking through the obstacles of the sluggish kinetics and polysulfides shuttle of the sulfur cathode at high sulfur loading for continuous high sulfur utilization during prolonged charge-discharge cycles. Herein, cobalt-doped carbon nanofibers containing carbon nanotubes (Co@CNF-CNT) were prepared via electrospinning and chemical vapor deposition (CVD) methods while using polyacrylonitrile (PAN) as the carbon source and cobalt nanoparticles as the catalyst. The obtained uniform thickness film with high mechanical strength can be cut and used directly as a functional freestanding interlayer for LSBs. The appearance of one-dimensional "dendritic" carbon nanotubes on the surface of carbon nanofibers not only enhanced the capture ability of lithium polysulfide (LPSs) but also further improved the conductivity of the materials and increased the electron transport path for Li2S deposition. The results show that under the synergistic effect of porous structure, nitrogen doping, cobalt nanoparticles, and high-conductivity carbon nanotubes, the Co@CNF-CNT interlayer can effectively raise the polysulfide adsorption and conversion efficiency, and provide remarkable rate performance and excellent cycling stability even at high sulfur mass loading. The LSBs with Co@CNF-CNT interlayer have a discharge capacity of 656 mAh g-1 at a high rate of 3C, and the capacity decay rate at 1C after 1000 cycles was only 0.045% per cycle. When fitted with a high sulfur loading cathode of 5.3 mg cm-2, the battery could still maintain a discharge capacity as high as 0.045% mAh g-1 after 70 cycles at 0.2C.