锂硫电池碳—硫复合材料中碳载体的杂化纳米结构设计和氮掺杂改性研究

发布时间：2018-04-14 07:09

本文选题：锂硫电池 + 碳-硫复合材料　；参考：《中南大学》2014年硕士论文

【摘要】：摘要：近年来,锂硫电池成为世界各国备受关注的新一代高能二次电池。在锂硫电池正极材料中,碳-硫复合材料是最有潜力的,并取得了很大的研究进展,但是仍存在一些问题,如中间产物在电解液中的溶解扩散,高倍率条件下电化学性能不理想,复合材料中硫含量低等。针对上述问题,本文在国家自然基金(51274240与51204209)的资助下,以锂硫电池碳-硫复合材料为研究对象,通过对碳载体的纳米杂化结构设计和氮掺杂改性研究,在一定程度上有效解决了这些问题。论文的主要内容和结论如下： (1)为解决多孔碳-硫复合材料中多硫化锂的溶解扩散问题,设计了由石墨烯(RGO)和介孔碳CMK-3两种碳材料构成的杂化纳米结构碳载体,并制备了复合材料RGO@CMK-3/S。包覆在CMK-3/S颗粒表面的RGO不仅能够进一步提高复合材料的导电性,而且能够起到物理阻隔的屏障和化学吸附的作用抑制或避免多硫化锂的扩散迁移。测试结果显示,0.5C倍率下,100次循环后,RGO@CMK-3/S仍能保持约734mAh·g-1的可逆比容量。 (2)为改善碳-硫复合材料在高倍率下的电化学性能,设计了由RGO和多壁碳纳米管网(MWCNTs-W)构成的三维杂化纳米结构碳载体,并制备了复合材料RG0@MWCNTs-W/S。在高温条件下,多壁碳纳米管经过KOH的化学活化作用后,管壁表面变得粗糙并引入了一些含氧官能团,这些缺陷有利于单质硫在MWCNTs-W中的均匀分布。由于MWCNTs-W和RGO能提供快速的电子和Li+传输通道,因此RGO@MWCNTs-W/S能够适应快速的电化学反应过程,5C倍率下,200次循环后可逆比容量高达620mAh g-1。 (3)采取化学还原法和高温热解法等方法制备了氮掺杂改性的多孔碳纤维(N-PCNF),随后制备了复合材料N-PCNF/S。氮掺杂不仅可以有效提高碳载体的导电性,而且还能在一定程度上改善碳载体对多硫化锂的吸附性能。测试结果表明,1C倍率下,200次循环后,含硫量为77.01wt%的N-PCNF/S依然表现出高达666.0mAh g-1的可逆比容量。因此,结合一维纳米结构和氮掺杂两方面优势对碳载体进行改性是另一种有效提高碳-硫复合材料电化学性能的途径。
[Abstract]:Abstract: in recent years, lithium-sulfur batteries have become a new generation of high-energy secondary batteries around the world.Among the cathode materials for lithium-sulfur batteries, carbon-sulfur composites are the most promising materials, and great progress has been made. However, there are still some problems, such as the dissolution and diffusion of intermediate products in the electrolyte.At high rate, the electrochemical performance is not ideal, and the sulfur content in the composites is low.In order to solve the above problems, this paper, supported by the National Fund for Nature, 51274240 and 51204209, studied the carbon / sulfur composite materials of lithium sulfur batteries through the design of nano-hybrid structure of carbon support and the modification of nitrogen doping.To a certain extent, these problems are effectively solved.The main contents and conclusions are as follows:In order to solve the problem of solubilization and diffusion of lithium polysulfide in porous carbon-sulfur composites, hybrid nanostructured carbon carriers composed of graphene (RGO) and mesoporous carbon (CMK-3) were designed, and the composite RGO-CMK-3 / S was prepared.RGO coated on the surface of CMK-3/S particles can not only improve the electrical conductivity of composites, but also inhibit or avoid the diffusion and migration of lithium polysulfide as a barrier of physical barrier and chemisorption.The results show that the reversible specific capacity of 734mAh g-1 can be maintained after 100 cycles at 0.5 C ratio.In order to improve the electrochemical performance of carbon-sulfur composites at high rate, a three-dimensional hybrid nanostructured carbon carrier composed of RGO and MWCNTs-WW was designed, and the composite RG0MWCNTs-W / S was prepared.At high temperature, the surface of multi-walled carbon nanotubes becomes rough and some oxygen-containing functional groups are introduced after the chemical activation of KOH. These defects are conducive to the uniform distribution of elemental sulfur in MWCNTs-W.Because MWCNTs-W and RGO can provide fast electron and Li transport channels, RGO@MWCNTs-W/S can adapt to the rapid electrochemical reaction process and the reversible specific capacity is as high as 620mAh g-1 after 200 cycles.(3) N-doped porous carbon fiber N-PCNFN was prepared by chemical reduction and pyrolysis at high temperature, then the composite N-PCNF / S was prepared.Nitrogen doping can not only effectively improve the conductivity of carbon support, but also improve the adsorption performance of carbon carrier to lithium polysulfide to some extent.The results showed that the reversible specific capacity of N-PCNF/S with sulfur content of 77.01 wt% was as high as 666.0mAh g-1 after 200 cycles.Therefore, it is another effective way to improve the electrochemical performance of carbon-sulfur composites by combining the advantages of one-dimensional nanostructure and nitrogen doping.
【学位授予单位】：中南大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TM912

【共引文献】