A freestanding and flexible nitrogen-doped carbon foam/sulfur cathode composited with reduced graphene oxide for high sulfur loading lithium–sulfur batteries

Abstract

Lithium–sulfur batteries have been considered to be the most promising candidate for next-generation chemical energy-storage technologies due to their high energy density and low cost. However, the low areal sulfur loading and notorious shuttle effect severely restrict the energy density and practical application of lithium-sulfur batteries. Herein, we employ a rational design concept to fabricate a nitrogen-doped carbon foam/sulfur cathode decorated with rGO based on commercial melamine foam. The as-prepared cathodes have robust flexibility and abundant internal voids that can enable them to be directly used as advanced self-supported high sulfur-containing electrodes with a loading of 3.2–8.8 mg cm⁻², meanwhile significantly accommodating the large volume change of sulfur. Based on the in situ nitrogen-doping and rGO decoration, the shuttle effect is also effectively inhibited via the chemical adsorption and physical immobilization of lithium polysulfide. Additionally, the close combination of a carbon skeleton and highly conductive rGO forms an interconnected 3D network that boosts electron and ion transport. Owing to these unique merits, the resultant cathodes deliver high capacity and excellent cycling performances with an ultrahigh capacity retention of 91% and a highly stable reversible capacity of 520 mA h g⁻¹ after 250 cycles at 0.5C. Even with a high sulfur loading (6.4 mg cm⁻²) and sulfur content (74%), a high initial discharge capacity of 913 mA h g⁻¹ (5.8 mA h cm⁻²) and an improved reversible capacity of 720 mA h g⁻¹ (4.6 mA h cm⁻²) are still achieved after 50 cycles at 0.1C.