锂硫电池凭借其高的理论能量密度(2600 W·h·kg-1)、丰富廉价的材料来源、且对环境友好等优势,而引起了人们的广泛关注.然而,锂硫电池活性物质导电性差、多硫化物易溶于有机电解液等问题所导致的硫正极倍率性能和循环稳定性差,仍然是困扰锂硫电池发展的挑战性难题.我们设计并以廉价易得的小分子化合物对苯二酚和甲醛为原料,通过缩聚反应、与氧化石墨烯原位复合、高温氮化制备了一类新型氮掺杂的碳纳米带固硫载体材料(NCNB-NG).通过NCNB-NG复合纳米硫进一步得到的碳硫复合正极材料(S@NCNB-NG)表现出更优异的倍率性能和循环稳定性,这主要得益于该碳质载体独特的微结构以及改善的导电性.%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) nano-composite 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 Na2S2O3 solution 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-1 at 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 1 after 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.
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