【作者】 王宏宇；

【导师】 尹鸽平；

【作者基本信息】 哈尔滨工业大学 ， 化学工程与技术， 2009， 硕士

【摘要】 硅基材料由于具有较高的理论容量而成为锂离子电池负极材料的研究热点,但是较大的体积变化造成了其电化学性能的急剧恶化。本文在概述了硅基材料研究现状的基础上,采用微乳液法和高温固相热解法制备了高性能硅/碳复合材料,并通过制备多孔硅材料进一步提高材料的电化学性能。分别以硅和硅/石墨混合物为原料,通过微乳液法制备球形硅基复合材料。研究发现加入硅/石墨混合物合成的球形硅/石墨/碳材料的循环性能更好,首次可逆容量为171.7mAh/g,40次循环容量保持率为88.6%。通过提高硅的含量,可以提高球形硅/碳复合材料的容量,首次可逆容量为864.6mAh/g,40次循环后可逆比容量为522.2mAh/g,容量保持率为60.4%,性能比纯硅电极提高很多。通过高温固相热解法制备硅/石墨/碳复合材料,研究了硅、石墨与沥青热解碳比例、极片热处理以及粘结剂种类对电极循环性能的影响。研究发现,硅:石墨:沥青热解碳质量百分比为25:55:20的材料(SGC255520)的性能最好,首次脱锂比容量为817.5mAh/g,50次循环后脱锂比容量为434.7mAh/g,容量保持率为53.2%。使用水性粘结剂并对极片进行热处理可以进一步提高材料的电化学性能,其中,SGC255520首次可逆比容量高达970.5mAh/g,50次循环后,材料的可逆比容量仍为782.7mAh/g,容量保持率为80.6%。当以SGC255520为原料,采用微乳液法合成球形材料时,材料首次可逆比容量为216.3mAh/g,40次循环容量保持率为90.6%,性能比球形硅/石墨/碳材料有所提高。由SiO材料制备得到了性能较好的多孔硅材料,并结合高温固相热解法和微乳液法合成了多孔硅基材料和球形硅基复合材料。研究发现,多孔硅/石墨/碳复合材料的首次可逆比容量高达642.7mAh/g,首次库伦效率为44.0%,100次循环后,可逆比容量仍为643.5mAh/g,容量保持率高达100.1%,表现出优异性能。当电解液中加入2%VC、和膏比为8:1:1时,首次效率分别提高至48.8%和65.3%。多孔硅/碳球形复合材料的性能与先前合成的球形材料相比,有了较大提高。首次可逆比容量为349.9mAh/g,随着循环的进行比容量逐渐上升并趋于平缓,100次循环后,可逆比容量为471.6mAh/g。更多还原

【Abstract】 Silicon-based anode is the hot topic for lithium ion battery due to the highest theoretical specific capacity, but the huge volume expansion/shrinkage brings the sharp decay of electrochemical properties. The dissertation summarized the advance of silicon-based node and proposed the inverse emulsion polymerization and high temperature pyrolysis methods to synthesize high performance silicon/carbon composite. Besides, porous silicon was used to enhance the electrochemical properties further.Based on the raw material of silicon or silicon/graphite, spherical composite was prepared by inverse emulsion polymerization method. The results showed that the spherical composite with silicon/graphite as raw material revealed better performance than that of silicon, which exhibited initial reversible capacity of 171.7mAh/g and the retention of 88.6% for 40 cycles. By adding more silicon into the silicon/graphite raw material, the obtained spherical composite showed much higher initial reversible capacity of 864.4mAh/g and remained 522.2mAh/g for 40 cycles with the retention of 60.4%, which was much better than the performance of silicon.Silicon/graphite/carbon composite was prepared by pyrolysis and the effects of proportion of the composite, heating of electrode and binder sorts on electrochemical performance were investigated. The result showed that the composite with the proportion of silicon:graphite:carbon=25:55:40 revealed better performance, which exhibited initial reversible capacity of 817.5mAh/g and remained 434.7mAh/g for 50 cycles with retention of 53.2%. In combination of heating of electrode and application of aqueous binder, the performance of the composite was enhanced obviously with the initial reversible capacity of 970.5mAh/g and the retention of 80.6% for 50 cycles. By making the composite into spherical shape, the composite showed relative lower capacity of 216.3mAh/g but much higher capacity retention of 90.6%.Porous silicon made from SiO showed much better performance and was incorporated into silicon/graphite/carbon composite in combination of pyrolysis and inverse emulsion polyrization methods. The results showed that the composite based on porous silicon revealed initial reversible capacity of 642.7mAh/g with efficiency of 44.0% but almost no decay for 100 cycles. In cases of adding 2wt.% VC into the electrolyte and adjusting the slurry proportion to 8:1:1 (active material:conductive carbon:binder), the composite exhibited initial efficiency of 48.8% and 65.3%. Compared with the above spherical composite with silicon as raw material, the spherical composite with porous silicon as raw material showed much better performance and delivered initial reversible capacity of 349.9mAh/g. After 100 cycles, the spherical composite remained the capacity of 471.6mAh/g.更多还原