基于多孔碳材料的新型高容量锂—硫电池正极材料制备及其电化学性能

发布时间：2018-07-08 20:32

本文选题：微型无人机 + 锂-硫电池　；参考：《南京航空航天大学》2014年硕士论文

【摘要】：锂-硫电池是以金属锂为负极，单质硫为正极的二次电池，因其具有高的理论比容量(1675mAh·g-1)及理论能量密度(2600Wh·kg-1),成为最具发展潜力的新型高能化学电源体系之一。另外，硫储量丰富、成本低廉，环境友好，是一种“绿色电池”。但是锂-硫电池仍存在一些问题：一是单质硫和它的还原产物硫化锂低电导率使其活性物质利用率低；二是硫电极的放电中间产物多硫化锂易溶于有机电解液中，这些易溶的多硫化锂进而扩散到锂负极，与负极锂反应生成低价多硫化锂，使负极锂腐蚀同时发生自放电。然后这些多硫化锂再扩散回到硫正极，从而引起活性物质的损失。这种“穿梭效应”的发生，严重制约了硫电极的循环稳定性。本文围绕提高硫的比容量以及循环稳定性的研究目的，制备性能优异的复合正极材料,为研制长航时微型无人机的电源系统提供理论和科学依据。主要研究内容包括： (1)硫被封装入以可溶性淀粉为碳源，针状纳米Mg(OH)2为模板制备的分级多孔碳(HPC)中。HPC具有高的比表面积902.5m2·g-1和大的孔体积2.60cm3·g-1。在S/HPC复合材料中硫含量高达84%。在高的电流密度1675mA·g-1下，S/HPC复合正极材料首次放电比容量高达1249mAh·g-1。经循环100圈，库伦效率高达94%，同时具有稳定的循环性能。S/HPC复合正极材料优良的电化学性能与HPC独特的结构密切相关。HPC具有大孔、介孔和微孔的分级多孔石墨结构。这种纳米结构的HPC能够在循环过程中缩短离子和电子的传输路径。 (2)以管状聚吡咯(T-PPY)为原料合成多孔氮掺杂的碳纳米管(PNCNT)，其具有高的比表面积(1765m2·g-1)和大的孔体积(1.28cm3·g-1)。PNCNT的内径和壁厚分别约为55nm和22nm。具有优异性质的PNCNT用于封装硫能够成为一个优异的复合正极材料应用于高性能锂-硫电池。在1C的电流密度下，S/PNCNT复合正极材料首次放电比容量为1341mAh·g-1。在50圈循环后，可逆比容量仍保持在933mAh·g-1。PNCNT良好的电化学性能归因于它自身优异的导电性，大比表面积，氮掺杂和独特的孔径分布。 (3)硫被限制在以金属有机框架化合物(MOF-5)一步法热解的分级多孔碳纳米片(HPCN)中。HPCN片层平均约50nm厚，呈现出三维的分级多孔纳米结构，具有高的比表面积(1645m2·g-1)和大的孔体积(1.18cm3·g-1)。电化学证明HPCN/S复合材料具有高比容量和良好的循环性能。在0.1C的电流密度下，HPCN/S的首次放电比容量为1177mAh·g-1。即使在0.5C的电流密度下，循环50圈后它的放电比容量仍然有730mAh·g-1，同时库仑效率高达97%。HPCN/S复合正极材料加强的电化学性能和HPCN优异的三维多孔片的纳米结构密切相关。这种结构在充放电过程中不仅可以提供稳定的电子和离子传输通道，而且对多硫化物强吸附作用和缓冲体积变化起到关键作用。 (4)以碳纳米管和氧化石墨烯(CNTs/GO)为主体材料，通过化学还原法制备了CNTs/GO负载硫的复合正极材料CNTs/GO/S。扫描电子显微镜(SEM)及透射电子显微镜(TEM)测试表明，，CNTs均匀插层在GO片间，从而形成三维多孔结构，有利于电解液的浸润；活性物质硫均匀地负载在CNTs/GO表面。电化学测试表明，CNTs/GO/S复合材料具有高的比容量和良好的循环稳定性：在1C电流密度下，复合材料首次放电比容量高达904mAh·g-1，经过50圈循环之后复合材料的比容量仍保持在578mAh·g-1。
[Abstract]:Lithium sulfur battery is the two battery with metal lithium as negative electrode and elemental sulfur as positive pole. Because of its high theoretical specific capacity (1675mAh. G-1) and theoretical energy density (2600Wh. Kg-1), lithium sulfur battery has become one of the most promising new high-energy chemical power systems. In addition, the sulfur reserves are rich, low cost and friendly environment. But it is a "green battery". There are still some problems in lithium sulphur batteries: one is the sulfur and its reduction product, the low conductivity of the lithium sulfide, low utilization of the active substance, and two is the intermediate product of the sulfur electrode, which is easy to dissolve in the organic electrolyte. These easily dissolved lithium sulfide and then spread to the lithium anode, and the reaction with the negative lithium can produce low sulfur and multi vulcanization. Lithium, which causes negative lithium corrosion at the same time, occurs at the same time from discharge. Then these lithium sulfide re diffuses back to the sulfur positive electrode, which causes the loss of the active substance. This "shuttle effect" seriously restricts the cyclic stability of the sulfur electrode. This paper focuses on the purpose of improving the specific capacity of sulfur and the stability of the cyclic sulfur. The positive pole material provides theoretical and scientific basis for developing the power supply system of the long endurance micro UAV.
(1) sulfur is encapsulated with soluble starch as carbon source and needle like nano Mg (OH) 2 as a template for graded porous carbon (HPC) with high specific surface area 902.5m2. G-1 and large pore volume 2.60cm3. G-1. in S/HPC composite materials with high current density 1675mA g-1. Up to 100 cycles, up to 100 cycles of 1249mAh. G-1., the efficiency of Kulun is up to 94%, and it has stable cyclic performance. The excellent electrochemical performance of the.S/HPC composite positive electrode is closely related to the unique structure of HPC..HPC has a porous graphite structure with large pores, mesoporous and microporous. This nanostructured HPC can shorten the ion and electricity during the cycle process. The transmission path of the child.
(2) synthesis of porous nitrogen doped carbon nanotube (PNCNT) with tubular polypyrrole (T-PPY) as a raw material, which has high specific surface area (1765m2. G-1) and large pore volume (1.28cm3. G-1).PNCNT, which has excellent properties for 55nm and 22nm., respectively, for encapsulation of sulfur, which can be used as an excellent composite positive material. Performance of lithium sulfur batteries. Under the current density of 1C, the initial discharge ratio of S/PNCNT composite cathode material is 1341mAh. G-1. at 50 cycles. The reversible specific capacity remains at 933mAh g-1.PNCNT good electrochemical performance due to its excellent electrical conductivity, large surface area, nitrogen doping and unique pore size distribution.
(3) sulfur is restricted to an average of about 50nm thickness in the.HPCN lamellar layer of graded porous carbon nanoscale (HPCN) by one step pyrolysis of metal organic framework compound (MOF-5), showing a three-dimensional porous nanostructure with a high specific surface area (1645m2. G-1) and large pore volume (1.18cm3. G-1). Electrochemistry shows that the HPCN/S composite has a high specific capacity. Under the current density of 0.1C, the initial discharge ratio of HPCN/S is 1177mAh. G-1., even at the current density of 0.5C, after 50 cycles, the discharge specific capacity is still 730mAh g-1, and the coulomb efficiency is higher than that of the 97%.HPCN/S composite positive electrode material and the excellent three dimensional porous film of HPCN. The structure of rice is closely related. This structure can not only provide a stable electron and ion transmission channel, but also play a key role in the strong adsorption of polysulfide and the change of the buffer volume.
(4) using carbon nanotubes and graphene oxide (CNTs/GO) as the main material, the CNTs/GO/S. scanning electron microscope (SEM) and transmission electron microscope (TEM) test of CNTs/GO supported sulfur based composite positive material by chemical reduction method showed that the uniform intercalation of CNTs was between the GO slices, thus forming a three-dimensional porous structure, which was beneficial to the infiltration of the electrolyte; The material sulfur is uniformly loaded on the CNTs/GO surface. The electrochemical test shows that the CNTs/GO/S composite has high specific capacity and good cyclic stability. At the 1C current density, the composite material's initial discharge capacity is up to 904mAh. G-1. After 50 cycles, the specific capacity of the composite remains at 578mAh g-1..
【学位授予单位】：南京航空航天大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：O613.71;TM912

【共引文献】