椰壳活性炭在锂硫电池正极材料中的应用

发布时间：2018-04-13 00:22

本文选题：活性炭 + 复合材料　；参考：《海南大学》2015年硕士论文

【摘要】：为了克服现今商业锂离子电池有限的能量密度问题,高能量密度二次电池已引起越来越多的关注。而其中,锂硫电池因其高理论比容量、5倍于商业化LiCoO2的高比能量而尤其被看好。不仅如此,单质硫元素还具有价格低廉、安全无毒以及来源丰富等优点。可是,单质硫与放电产物的电导率低以及自身的穿梭效应的存在,造成其商业化进程一直迟缓。为了解决这些问题,研究者们越来越多把目光投入到构建可调的微纳米结构正极材料并与硫复合,而其中硫碳复合材料往往表现出稳定的电化学性能。因此,本文利用海南优势资源椰壳制备高比表面积的活性炭为基底制备硫碳复合材料,并采用XRD、SEM、EDS、TGA以及电化学测试等手段对复合材料进行表征与测试,讨论了椰壳基活性炭作为锂硫电池正极材料的可能性。利用KOH活化法制备椰壳基多孔活性炭,通过对比实验表明,经过KOH的活化处理得到了比表面积达2258.7m2/g的高孔隙率、高比表面积的椰壳基活性炭(HSAAC)。其孔结构主要以微孔为主并存在部分的介孔结构。并用于锂硫电池的制备,经过电化学测试发现由于其比表面积大、吸附性能强等特点,复合材料在200mA/g的电流密度下首次放电比容量高达1230mAh/g,100次循环之后仍然得到929mAh/g的可逆比容量,表现出了较好的电化学性能。开展了椰壳基多孔活性炭为原料,采用氨水、双氧水浸责法对其进行改性,探讨了多孔活性炭官能团改性对锂硫电池电化学性能的影响。傅里叶红外图谱表明,双氧水改性活性炭在其表面引入了羧基基团而氨水改性活性炭在其表面引入了氨基基团。经电化学测试可发现氨水改性引入了大量的氨基,能显著提高锂硫电池的首次放电比容量,由1058mAh/g提高至1333mAh/g;而双氧水改性在引入了羧基基团,其首次充放电比容量以及充放电循环性能都受到了负面影响。通过改变制备工艺参数得到不同孔结构椰壳基多孔活性炭,并用于锂硫电池制备及电化学测试,研究了具有不同比表面积、孔结构的椰壳基多孔炭负载单质硫制备复合材料的电化学性能及孔结构对其性能的影响。结果表明：随着微孔比例上升、中孔比例下降、比表面积增加,制备得的锂硫电池比容量逐步提高。其中性能最优样品为介孔率为15%,首次放电比容量最高达1294.5mAh/g,进行了100次充放电循环可逆比容量达到809.3mAh/g.说明微孔结构使得椰壳基活性炭比表面积增加,吸附性能提高,能有效抑制锂硫电池的穿梭效应,对锂硫电池电化学性能有着积极的影响。
[Abstract]:In order to overcome the limited energy density of commercial lithium ion batteries, high energy density secondary batteries have attracted more and more attention.Among them, lithium-sulfur batteries are particularly promising for their high theoretical specific capacity of 5 times higher specific energy than commercial LiCoO2.Moreover, elemental sulfur has the advantages of low price, safe and non-toxic and abundant sources.However, the low conductivity of sulfur and discharge products and the existence of its own shuttle effect make its commercialization process slow.In order to solve these problems, researchers are focusing more and more attention on the fabrication of adjustable micro-nano structure cathode materials and compounding with sulfur, among which sulfur and carbon composites often exhibit stable electrochemical properties.Therefore, sulfur and carbon composites were prepared on the basis of high specific surface area activated carbon prepared from coconut shell, a dominant resource in Hainan. The composites were characterized and tested by means of XRDX, SEM, EDSGA and electrochemical measurements.The possibility of coconut shell based activated carbon as cathode material for lithium-sulfur battery was discussed.Coconut shell based porous activated carbon was prepared by KOH activation method. The results showed that the activated carbon with high specific surface area (2258.7m2/g) and high specific surface area (2258.7m2/g) were obtained by KOH activation.The pore structure mainly consists of micropores and some mesoporous structures.And it was used in the preparation of lithium-sulfur battery. It was found by electrochemical test that due to its large specific surface area and strong adsorption properties, the first discharge specific capacity of the composite at current density of 200mA/g was as high as 1230mAh/ g / g / 100 cycle, and the reversible specific capacity of 929mAh/g was still obtained after 100 cycles.It shows good electrochemical performance.The coconut shell based porous activated carbon was modified with ammonia and hydrogen peroxide. The effect of functional group modification of porous activated carbon on the electrochemical performance of lithium sulfur battery was discussed.Fourier transform infrared spectroscopy (FTIR) showed that hydrogen peroxide modified activated carbon introduced carboxyl groups on its surface and ammonia modified activated carbon introduced amino groups on its surface.It was found by electrochemical test that a large amount of amino groups were introduced into the modification of ammonia, and the first discharge specific capacity of lithium-sulfur battery was increased from 1058mAh/g to 1333mAh / g, while the carboxyl group was introduced in the modification of hydrogen peroxide.The first charge-discharge specific capacity and charge-discharge cycle performance are all negatively affected.The porous activated carbon based on coconut shell with different pore structure was obtained by changing the preparation process parameters, and was used in the preparation and electrochemical measurement of lithium sulfur batteries. The specific surface area of the activated carbon with different pore structure was studied.Electrochemical properties of composites prepared by porous carbon supported on porous carbon with porous structure and the effect of pore structure on the properties of composites were investigated.The results show that with the increase of the ratio of micropores, the ratio of mesoporous cells decreases, the specific surface area increases, and the specific capacity of the prepared lithium-sulfur batteries increases gradually.The optimum performance of the sample is the mesoporous ratio of 15, the first discharge specific capacity of 1294.5mAh-1 / g, and the reversible specific capacity of 809.3 mAh/ g for 100 charge-discharge cycles.The results show that the micropore structure can increase the specific surface area of coconut shell activated carbon and enhance the adsorbability of activated carbon. It can effectively inhibit the shuttle effect of lithium sulfur battery and has a positive effect on the electrochemical performance of lithium sulfur battery.
【学位授予单位】：海南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TM912

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