High Conductive Carbon Nanofiber-Graphite Paper Electrodes with Ultrahigh Polysulfide-Loading for Advanced Lithium-Sulfur Batteries

Lithium sulfur (Li-S) battery has attracted much attention due to its high energy density and the abundance of sulfur on the Earth, but some major problems including short cycle life, low sulfur loading, and inferior sulfur utilization have impeded its practical applications. Here, we report a rational combination of conductive carbon nanofiber-graphite paper (CNGP) with dissolved polysulfides to the formation of advanced sulfur cathode structures that can take full advantage of each building block. The hierarchical CNGP electrode has an ultrahigh sulfur loading of 6.7 mg cm^-2, and a high electrical conductivity of 328 S cm^-1. In the CNGP electrode, the integrated carbon nanofiber paper (~100 μm) with extremely low density (2.1 mg cm^-2) is used as current collector and carrier for the dissolved Li₂S₆ species, while the densely tapped graphite film (~5 μm) on the top of CNF acts as a protection layer to prevent migration of the dissolved polysulfides from the cathode to the anode. The use of CNGP electrodes and dissolved Li₂S₆ species enables the fabrication of remarkably improved Li-S batteries with a reversible capacity of 750 mAhg^-1 over 300 cycles at 1 C, and 80% of capacity retention from 720 to 580 mAhg^-1 over 500 cycles at 1.5 C with an average Coulombic efficiency of 99.5%. The results provide important progress towards the fabrication of Li-S batteries with long cycle life and high rate capabilities.