【作者】 徐子敬；

【导师】 施毅； 郑明波；

【作者基本信息】 南京大学 ， 微电子学与固体电子学， 2011， 硕士

【摘要】 锂离子二次电池已成为21世纪极具发展潜力的新型化学电源。目前,商用化锂离子电池广泛采用的负极材料为石墨类碳,该类材料理论储锂容量较低(372mAh/g),无法满足电子器件的发展需求。因而需要研究开发新型高能锂离子电池负极材料。硅基材料由于其极高的理论储锂容量(4200 mAh/g,对应于Li4.4Si合金相),极具应用前景。然而,硅基材料在合金、退合金化过程中引入的巨大体积形变(>300%),导致材料的破碎及导电网络的破坏,极大限制了硅基材料的循环性能。近年来,随着纳米技术的快速发展,硅基纳米复合物材料在锂离子电池中的应用成为引人注目的研究热点并取得了较大进展,有望成为取代石墨类碳的新一代高性能负极材料。作为锂离子电池电极材料,硅基纳米材料具有许多独特的物理和化学性质,如更佳的承受体积应变能力、比表面积大、锂离子脱嵌的深度小、离子扩散路径短、可逆容量高、循环寿命长等。因此,硅基纳米材料用于锂离子电池可以显著提高电池的比容量和充放电性能,是新一代锂离子电池发展的重要方向。本工作致力于硅基纳米结构(硅基纳米线阵列、多孔硅微球颗粒)的低成本、高产量制备、碳包覆以及在锂离子电池中的应用。具体研究工作如下：1.通过金属纳米颗粒辅助刻蚀方法对单晶硅衬底进行电化学刻蚀,于室温下通过HF/H2O2/H2O混合刻蚀溶液快速制备出大面积、高质量、方向均一的单晶硅纳米线阵列,并探讨了刻蚀机理以及刻蚀条件(沉积液配比,时间等)对纳米线形貌的影响。此外,利用介孔碳填充硅基纳米线阵列间的空隙,增加纳米线阵列的导电性及结构稳定性,该结构有望改善硅基纳米线阵列的锂电性能。2.利用镁热还原技术将SiO2蛋白石还原为多孔硅微球块体,首次低成本制备出由多孔硅微球组装成的块体材料,分别通过XRD、SEM和充放电性能测试等表征手段对该材料进行成分、结构、形貌和电化学性能表征,SEM结果表明镁热还原法制备的硅微球直径约400 nm,微球内部包含大量纳米孔道,微球颗粒间接触良好,具有宏观块体形貌。进一步利用低分子量酚醛树脂填充硅微球内部的纳米孔道并高温碳化,得到硅/碳复合材料。电化学测试结果表明：无定形碳填充有效改善块体材料的结构稳定性及导电性能,循环20次后容量为1200mAh/g。3.以低分子量酚醛树脂及单晶硅纳米颗粒为原料,通过聚合及700℃碳化生成核-壳结构Si@C纳米颗粒。分别通过SEM、TEM和充放电性能测试等表征手段对该材料进行结构、形貌和电化学性能表征,电化学测试结果表明,无定形碳包覆极大的增强了硅基材料循环性能,首次放电容量达到1600 mAh/g,循环30次后仍能保持700 mAh/g的容量,表现出良好的电化学性能。更多还原

【Abstract】 Lithium-ion secondary battery has been considered as the most promising power sources in the 21st century. The commercial lithium-ion batteries usually select graphite as the anode material. The capacity of such material is merely 372 mAh/g, which is insufficient for meeting the needs of future electronic equipment. The need for high-energy and lighter lithium-ion batteries product seeks for new large capacity anode material candidates. Silicon-based materials are promising candidates for lithium-ion battery anode electrodes for their extremely high theoretical capacity (approximately 4200 mAh/g, with the formation of Li4.4Si alloy). However, the dramatic volume swing (>300%) during alloying/de-alloying processes causes the pulverization of the electrode materials and breakdown of the electrically conductive network, which restricts the cycle performance seriously. In recent years, with the rapid development of nano-technology, the application of silicon-based nano-materials in the lithium-ion battery has progressed a lot. They are expected to be used as a new generation of high-performance anode materials instead of carbon materials. As lithium-ion battery anode electrodes, silicon based nano-materials have some unique physical and chemical properties, such as better accommodation of the lithiation and delithiation strain, larger surface area, shorter transport length, high reversible capacity and long cycle life. These properties can significantly improve specific capacity and high rate performance of lithium-ion batteries. This study is mainly devoted to the fabrication of silicon-based nanostructure (silicon nanowires and porous silicon microspheres) at low cost and high throughput, the carbon coating, and the application in lithium-ion battery. The detailed contents and results in this dissertation include:1. Large-area, high quality, highly oriented single-crystalline silicon nanowires (SiNWs) were prepared by using metal-assisted etching method of silicon in HF/H2O2/H2O solutions with Ag nanoparticles as catalyst agents at near room temperature. The influence of the etching solution composition and the etching time in the etching process was studied. Besides, mesoporous carbon was filled in the SiNWs by using the resol/surfactant mixture to fill the SiNWs. Such structure greatly enhances the conductivity as well as structure stability of SiNWs, and will be applied in lithium-ion batteries.2. Magnesiothermic reduction technology was used for converting nanostructured silica OPAL into porous silicon microspheres. The as-prepared samples possessed crystalline characteristics according to XRD analysis. SEM images showed that the silicon microspheres has an average size of about 400 nm and possessed nanoporous structure. In addition, Si/C nanocomposites were prepared by using the resol to fill the nanopores of the silicon microspheres and further carbonization. The electrochemical test indicated that the carbon coating greatly enhanced the structure stability and electrical conductivity of silicon microspheres. The Si/C nanocomposites exhibited a stable reversible capacity of 1200 mAh/g after 20 cycles.3. The nanostructured Si@C spheres with silicon cores and carbon shells were prepared by coating silicon nano-particles with resol and further carbonization at 700℃. These Si@C core-shell spheres exhibited an initial discharge specific capacity of 1600mAh/g in the potential range of 1.1-0.01 V. After 30 cycles, the capacity of the Si@C core-shell spheres anode stabilized reversibly at about 700mAh/g.更多还原