Preparation of three-dimensional nitrogen-doped carbon nanoribbon and application in lithium/sulfur batteries

Abstract

Lithium/sulfur (Li-S) batteries have recently attracted intensive research interests due to their high theoretical specific energy of 2600 W•h•kg-1. However, the poor electronic conductivity of sulfur and the high solubility of polysulfides in organic electrolytes lead to poor cycling stability and rate capability. Herein, we report a three-dimensional (3D) nanocomposite network made from nitrogen-doped carbon nanoribbon (NCNB) and nitrogen-doped graphene (NG), which has a high electronic conductivity and can serve as a conductive matrix and a sulfur immobilizer for the sulfur cathode. The NCNB is prepared by thermal nitridation of a unique 3D phenolic resin (PHF) isolated from the polycondensation reaction of 1,4-hydroquinone and formaldehyde. The N content of NCNB-NG can reach as high as 9.7 wt%. Although three types of N bonding geometries, including pyridinic N, pyrrolic N, and graphitic N, are identified in the NCNB-NG composites, we found the pyridinic N is dominant, which facilitates the trapping of intermediate lithium polysulfides. The sulfur was loaded on NCNB-NG by using a Na2S2O3solution as sulfur source. The scanning electron microscope (SEM) images show that almost no large S particle can be observed in the as-prepared S@NCNB-NG nanocomposites, suggesting a uniform coating of S on the NCNB-NG networks. The transmission electron microscopic (TEM) images and the elemental mapping by Energy-Dispersive X-ray (EDX) analysis also show that nano-sized S particles are uniformly distributed on the NCNB-NG matrix. The as-obtained S@NCNB-NG cathode can deliver a high specific capacity of 1338 mA•h•g-1at 0.05 C with about 80% S utilization. It also exhibits excellent rate capability and good cycle stability with a retained specific capacity of 556 mA•h•g-1after 300th cycles. These performances are much higher than the control samples using the S@NCNB and the S@PHF nanocomposites as cathodes. The improved performance can be attributed to the unique microstructure and the improved electronic conductivity of the NCNB-NG matrix.