Three-Dimensional Nitrogen-Doped Carbon Nanoskeleton Cladded with a Graphitic C₃N₅ Nanolayer as a Sulfur Host for Lithium-Sulfur Batteries

Active site and morphology engineering are essential for the electrochemical performance of carbon-based nanomaterials. In this study, we proposed a three-dimensional (3D) N-doped carbon skeleton cladded with a g-C3N5 nanolayer (denoted as CS/U-C3N5-K) as a sulfur host for lithium-sulfur batteries (LSBs). A 3D N-doped carbon nanoskeleton (CS/U) was presynthesized by carbonizing mixed precursors composed of chitosan and urea. The g-C3N5 nanolayer was cladded over the carbon nanoskeleton via pyrolyzing a mixture of CS/U and 3-amino-1,2,4-triazole. KOH was also introduced into the mixture to generate additional intrinsic carbon defects in CS/U-C3N5-K. The porous graphitic carbon nanoskeleton ensured good electrical conductivity and sulfur-based species penetration. The abundant nitrogen-based moieties in the carbon nanoskeleton and g-C3N5 nanolayer, as well as intrinsic carbon defects, can redistribute the electrons and offer massive active sites for the sulfur redox reaction process. The as-obtained CS/U-C3N5-K nanocomposite delivered ameliorative sulfur redox reaction kinetics, including reduced charge transfer resistance, reasonable redox polarization, enhanced LiPS chemisorption and trapping capability, and a smaller potential difference for Li2S nucleation/activation. The LSB with CS/U-C3N5-K as a sulfur host material exhibited capacities of 1076.1 and 696.8 mAh g(-1) at 0.2 for the initial and 200th cycles, respectively. The CS/U-C3N5-K cathode also exhibited capacities of 624.9 and 402.9 mAh g(-1) at 2C for the initial and 1000th cycles, respectively. This work offers a feasible strategy for the engineering of active sites and morphology of metal-free carbon-based nanomaterials in electrochemical energy conversion and storage fields.