超级活性炭的结构及其电化学性能研究

发布时间：2018-05-15 05:03

本文选题：超级活性炭 + 结构　；参考：《华东理工大学》2017年硕士论文

【摘要】：超级活性炭具有巨大的比表面积、孔径分布相对集中、低灰份和良好的导电性等特点,在电化学储能领域具有广泛的应用前景。碱法活化,特别是KOH活化石油焦是目前常用的制备超级活性炭方法,但其工业化制备仍存在诸多产品质量问题。在前期攻克KOH活化过程中反应器内部传质优化技术、金属钾的安全处理技术、低灰份控制技术、粒径控制技术、表面处理技术基础上,我们成功制备出30吨/年规模超级活性炭产品。本文以此材料为主要原料,分析了其物化结构,对比了其与商业电容活性炭的物性差异,考察了其在超级电容器及Li-S电池正极中的电化学应用性能,得到结论如下:(1)以石油焦为原料、KOH为活化剂,吨级规模制备出超级活性炭粗品,进一步通过灰份控制、粒径控制、表面后处理技术,得到超级活性炭产品(SAC)。其主要性能指标如下:平均粒径～5 μm,振实密度0.35 g/cm3,电导率4 S/cm,比表面2000 m2/g,平均孔径1-3 nm,灰分0.07 wt%,氧含量2 wt%。与商业化电容活性炭相比,所制SAC具有最高的比表面积、最低的灰分和氧含量、相对集中的粒径分布。(2)当用于超级电容器电极材料时,在Et_4NBF_4/PC体系,SAC的比容量在0.5 A/g时为122 F/g,在10 A/g时的比容量是104.6 F/g,仅下降了 14%,循环5000次后容量保持率为94.5%,性能优于目前商业电容活性炭。进一步对比了 SAC在SBPBF4/PC和Et4NBF4/PC电解液体系中的电化学行为。由于SBP+具有较小的离子半径,SAC在SBPBF4/PC中的比容量比在Et4NBF4/PC中高10%,且正负极容量对称性更佳,5000次循环容量保持率为96.2%。(3)探讨了 SAC在高性能Li-S电池正极材料中的应用潜力。首先以SAC为单质硫载体材料,采用熔融浸渍法得到SAC/S复合材料。由于SAC丰富的微孔结构可以对多硫离子产生较强的限域作用,SAC/S在0.5C时的首次放电比容量为870mAhg~(-1),经过300次循环,容量保持率为67%。其次以SAC作为功能性涂层,直接涂覆在硫电极或商业化隔膜的表面来抑制长链聚硫化物向负极的穿梭。正极涂覆和隔膜涂覆都能显著提升锂硫电池的放电容量和循环稳定性。但是正极涂覆层在循环过程中有可能因为电极体积变化而破裂,失去保护作用,相比之下,隔膜涂覆层则能保持较好的稳定性。当使用隔膜涂覆层,硫正极在0.5 C时的首次放电容量为1320 mAh g~(-1),经过100次循环后,可逆容量为997 mAh g~(-1),容量保持率为76%,在3 C时仍能获得673 mAh g~(-1)的可逆容量。
[Abstract]:Super activated carbon has the characteristics of large specific surface area, relatively concentrated pore size distribution, low ash content and good electrical conductivity, etc. It has a wide application prospect in the field of electrochemical energy storage. Alkaline activated petroleum coke, especially KOH activated petroleum coke, is a commonly used method to prepare superactivated carbon. However, there are still many problems in the industrial preparation of petroleum coke. On the basis of mass transfer optimization technology in reactor, safety treatment technology of potassium metal, low ash content control technology, particle size control technology and surface treatment technology in the early stage of KOH activation, We successfully prepared 30 tons / year scale super-activated carbon products. In this paper, the physical and chemical structure of this material was analyzed, the physical properties of the material were compared with commercial capacitor activated carbon, and the electrochemical application performance of the material in supercapacitor and Li-S battery positive electrode was investigated. The conclusion is as follows: (1) Super-activated carbon was prepared by using petroleum coke as raw material Koh as activator and tonnage scale. Further, through ash control, particle size control and surface post-treatment technology, the super activated carbon product was obtained. The main performance parameters are as follows: average particle size is 5 渭 m, vibrational density is 0.35 g / cm ~ 3, conductivity is 4 S / cm, specific surface is 2000 m ~ 2 / g, average pore size is 1-3 nm, ash content is 0.07 wt, oxygen content is 2 wt. Compared with commercial capacitive activated carbon, the SAC has the highest specific surface area, the lowest ash and oxygen content, and the relatively concentrated particle size distribution. The specific capacity of Et_4NBF_4/PC is 122F / g at 0.5 Ag and 104.6 Fr / g at 10A / g, which is only 14 times lower. After 5000 cycles, the capacity retention rate is 94.5%, which is superior to the current commercial capacitive activated carbon. The electrochemical behavior of SAC in SBPBF4/PC and Et4NBF4/PC electrolytes was further compared. Due to the fact that the specific capacity of SBP in SBPBF4/PC is 10% higher than that in Et4NBF4/PC, and the positive and negative electrode capacity symmetry is better than that in Et4NBF4/PC, the capacity retention rate of 5000th cycle is 96. 2%. The potential application of SAC in the cathode material of high performance Li-S battery is discussed. Firstly, SAC/S composites were prepared by melt impregnation with SAC as the carrier of sulfur. The initial discharge specific capacity of SAC / S at 0.5 C is 870 mg / g ~ (-1) because the rich micropore structure of SAC can have a strong limiting effect on polysulfide ions. After 300 cycles, the capacity retention rate is 6770 m 路g ~ (-1) 路L ~ (-1) 路L ~ (-1) 路L ~ (-1) 路L ~ (-1) 路L ~ (-1). Secondly, SAC was used as the functional coating, which was directly coated on the surface of sulfur electrode or commercial diaphragm to inhibit the shuttle from long chain polysulfide to negative electrode. Both positive electrode coating and diaphragm coating can significantly improve the discharge capacity and cycle stability of lithium-sulfur batteries. However, the positive electrode coating may break down due to the change of electrode volume during the cycling process, and lose its protective effect. In contrast, the diaphragm coating can maintain better stability. When the membrane is coated, the initial discharge capacity of the sulfur positive electrode is 1320 mAh / g ~ (-1) at 0. 5C. After 100 cycles, the reversible capacity is 997 mAh / g ~ (-1) and the capacity retention is 76 ~ (-1), and the reversible capacity of 673 mAh / g ~ (-1) can be obtained at 3 C.
【学位授予单位】：华东理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ424.1

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