锂硫电池正极改性、结构设计及电化学性能研究

发布时间：2018-04-18 20:45

本文选题：锂硫电池 + 硫正极　；参考：《中南大学》2014年博士论文

【摘要】：摘要：锂硫电池是一种极具发展潜力的高能量密度二次锂电池,其正极材料单质硫具有比容量大、成本低廉、环境友好等优点。然而,硫正极也存在诸多缺点：(1)硫及还原产物常温下具有电子绝缘性；(2)硫电极在充放电过程中会形成易溶于电解液的多硫化物并产生穿梭效应；(3)硫电极在充放电循环中存在较大的体积效应。这些因素造成锂硫电池活性物质利用率低、循环性能差、倍率性能不理想,阻碍了锂硫电池的实用化。围绕解决硫电极存在的关键问题,本论文从设计、构筑硫基复合材料和电极结构出发,开展了多方面对硫正极的改性研究工作。本文系统研究了不同碳材料对于碳硫复合材料结构和性能的影响；采用喷雾热分解法制备了锂硫电池新型碳硫复合正极材料；研究了多功能碳纸用于硫正极集流体的电化学性能；采用磁控溅射和电化学沉积导电膜的方法对硫正极进行了极片修饰；设计并制备了新型锂硫电池正极结构和导电隔层,研究了其独特的电化学性能及作用机理。具体研究结果如下：采用液相原位沉积的方法制备了碳纳米管／硫(CNT/S)、碳纤维／硫(CNF/S)、活性碳／硫(AC/S)和导电炭黑／硫(SP/S)复合材料,对四种材料的测试结果比较表明：碳材料的结构和形貌是影响复合效果的关键因素；多孔碳材料较无孔或少孔碳材料更能改善硫正极的循环稳定性和提高活性物质利用率；CNT/S和AC/S复合材料表现出较好的电化学性能,CNT能提高复合材料导电性,但复合均匀度欠佳,实际入孔的有效载硫量有限；AC能有效吸附活性物质硫,但导电性欠佳。采用喷雾热分解法,以Si02为模板制备了比表面积达1133m2g-1总孔容为2.75cm3g-1的介孔碳球(SPC),并以此作为负载硫的导电基体,制备了介孔碳球／硫复合材料(SPC/S)。电化学研究表明,碳球的三维结构可以有效增强复合材料的循环稳定性,0.2C倍率下循环50次的容量为637mAh g-1,循环容量保持率为62.9%。此外,碳球内部的介孔有利于硫的纳米化,能起到限域捕捉活性物质和缩短离子扩散路径的作用,有利于提高材料的倍率性能,1C倍率下仍有470mAh g-1的容量。在硫正极制备工艺方面,引入商业碳纸用作正极集流体。电化学研究表明,碳纸作集流体能显著改善硫正极的循环稳定性,0.2C倍率下循环100次容量仍有786mAh g-1,循环容量保持率为89.6%。在正极构造中,碳纸既能作为集流体,又能作为负载活性物质硫的基体,限域和捕捉溶解的多硫化物,具备多重功能。这种显著的改善归因于碳纸具有优异的导电性和多孔网络骨架结构。在正极修饰方面,采用磁控溅射喷涂导电碳膜修饰SPC/S复合正极,0.5C倍率下,镀碳SPC/S复合正极首次放电容量为956mAh g-1,50次循环后容量保持在642mAh g-1,容量保持率提高到67.2%；采用电化学沉积聚苯胺(PANI)导电膜修饰纯S正极,0.2C倍率下,PANI涂层S正极首次放电容量为1094mAh g-1,100次循环后容量保持在725mAh g-1,容量保持率提高到66.3%。研究表明,磁控溅射镀碳能有效增强电极导电性,减少碳硫复合材料中活性物质的不可逆损失；电化学沉积PANI能形成导电纳米网状结构,有效束缚活性物质硫,减小多硫化物的溶解和扩散。在正极结构设计方面,设计并制备了两种在正极和隔膜之间含隔层的锂硫电池：采用简单的滤纸碳化工艺获得了性能优良的导电碳纸；采用简单的商业镍网压制工艺获得了结构稳定的导电镍网,分别引入到传统锂硫电池中作为隔层使用,其电化学性能获得了显著改善。0.2C倍率下,碳纸隔层电池50次循环后容量保持在810mAh g-1;镍网隔层电池80次循环后容量保持在640mAh g-1。碳纸和镍网隔层的改善作用归因于它们优良的导电性和多孔网络结构,能够为绝缘的放电产物提供导电支撑,缓解体积变化,以及吸附多硫化物。
[Abstract]:Abstract: lithium sulfur battery is a lithium battery with high energy density two times a great potential for development, the sulfur cathode material which has large capacity, low cost, environment friendly and other advantages. However, there are also many disadvantages: sulfur cathode (1) with electronic insulation and sulfur reduction products at room temperature (2); the sulfur electrode during the charge discharge process will form polysulfide soluble in the electrolyte and the shuttle effect; (3) there are large volume effect of sulfur electrode during charge / discharge cycles. These factors lead to low utilization of active material of lithium sulfur batteries, poor cycle performance, rate performance is not ideal, hindered the lithium sulfur battery practical.
The key to solve the problem of sulfur electrode existed, this paper from the design, construction of sulfur based composite materials and electrode structure, carry out modification on aspects of sulfur cathode. This paper studied the effect of carbon materials on the structure and performance of carbon sulfur composite; carbon sulfur composite cathode material for lithium sulfur battery prepared by spray thermal decomposition; multi functional carbon paper for the electrochemical performance of sulfur cathode collector was studied; by magnetron sputtering and electrochemical deposition of conductive films were modified on electrode and lithium sulfur cathode; design new cathode structure of sulfur battery and conducting interlayer was prepared and its electrochemical performance was studied and the unique role the mechanism of the specific research results are as follows:
Carbon nanotubes / sulfur were prepared by the method of liquid phase in situ deposition system (CNT/S), carbon fiber / sulfur (CNF/S), activated carbon / sulfur (AC/S) and carbon black (SP/S) / sulfur composites, compared to the four kinds of material test results: the structure and morphology of carbon materials is a key factor affecting composite effect; porous carbon materials is non porous or less porous carbon materials can improve the cycle stability of sulfur cathode and improve the utilization of active material; CNT/S and AC/S composites showed good electrochemical performance, CNT can improve the conductivity of composites, but the composite uniformity is poor, the actual effective load of sulfur into the hole limited; AC can effectively adsorb active substances of sulfur, but the conductivity is poor.
By spray thermal decomposition method, template preparation for mesoporous carbon spheres 2.75cm3g-1 specific surface area of 1133m2g-1 Kong Rong Si02 (SPC), and as the conductive base load of sulfur, mesoporous carbon spheres / sulfur composite materials were prepared (SPC/S). The electrochemical results show that the three dimensional structure of carbon spheres can effectively enhance the cycle stability of composite materials, 0.2C rate 50 cycles the capacity of 637mAh g-1, cyclic capacity retention rate was 62.9%. in addition, the ball inside the mesopores favoring the carbon sulfur nano, can play a role to capture the confinement of active substances and shorten the ion diffusion path, is conducive to improve the rate performance the 1C rate is still 470mAh g-1 capacity.
In the sulfur cathode preparation process, the introduction of commercial carbon paper used as cathode collector. The electrochemical results show that the carbon paper set fluid can significantly improve the cycle stability of sulfur cathode, the 100 Capacity Circulating 0.2C rate is 786mAh g-1, the cycling capacity retention rate of 89.6%. in the cathode structure, carbon paper can be used as collector, and can load active material as the matrix of sulfur and polysulfide confinement and capture dissolved, with multiple functions. This significant improvement is attributed to carbon paper has excellent conductivity and porous structure.
For the modification of cathode by magnetron sputtering coating conductive carbon film modified SPC/S composite cathode, 0.5C, carbon coated SPC/S composite cathode discharge capacity of 956mAh g-1,50 cycling in 642mAh g-1, the capacity retention rate increased to 67.2%; the electrochemical deposition of poly aniline (PANI) pure S anode conductive film modified 0.2C. PANI coated S cathode, the first discharge capacity was 1094mAh g-1100 cycling in 725mAh g-1, the capacity retention rate increased to 66.3%. study showed that the magnetron sputtered carbon can effectively enhance the conductivity of the electrode active material, reduce the carbon sulfur composite material in irreversible loss; electrochemical deposition of PANI can form a conductive nano network structure effective restraint, active material dissolution and diffusion of sulfur, reduce sulfur.
In the cathode structure design, and design two kinds of lithium sulfur battery between the anode and diaphragm containing interlayer were prepared: the excellent properties of the conductive carbon paper by paper carbonization process is simple; the structural stability of the conductive nickel net using a simple commercial nickel net pressing process, was introduced into the traditional lithium used as interlayer the electrochemical performance of sulfur battery, obtained significantly improved.0.2C, capacity to maintain the 810mAh g-1 carbon paper layer battery after 50 cycles; nickel net interlayer battery capacity after 80 cycles in effect 640mAh g-1. carbon paper and nickel net layer due to their excellent electrical conductivity and porous network structure, can provide conductive support for the discharge products of the insulation, relieve volume change, and adsorption of polysulfides.

【学位授予单位】：中南大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM912

【参考文献】