【作者】 于敬学；

【导师】 阙端麟； 杨德仁； 张辉；

【作者基本信息】 浙江大学 ， 材料科学与工程， 2014， 博士

【摘要】 近年来,便携式电子设备、电动工具以及电动汽车技术的高速发展对锂离子电池的性能提出了更高的要求,从而激发了新一代高比容量、长循环寿命的锂离子电池负极材料的研究。与目前商用的碳类负极材料相比,硅、锗基负极材料具有更高的比容量与能量密度,因此被认为是有潜力的下一代锂离子电池负极材料。但是硅、锗基负极材料在充放电循环过程中产生了巨大的体积变化,这会导致电极材料的粉碎以及电极导电网络的崩溃,从而使循环性能急剧衰减。通过构建特定的硅、锗基微纳结构以及与碳等材料复合等手段,能够在一定程度上改善硅、锗基负极材料的循环寿命。但是,目前国内外的研究仍然没有完全解决上述问题。因此,进一步设计和制备硅、锗基纳米负极材料,改善锂离子电池负极材料的充放电性能具有重要意义。本文通过无电金属沉积法合成了硅纳米线与多孔硅颗粒,利用模板法合成了硅锗复合材料一维纳米结构阵列,利用固相热分解法合成了多孔锗颗粒。在此基础上,研究了上述材料作为锂离子电池负极材料的性能,取得了以下主要创新成果：(1)利用无电金属沉积的方法,以单晶硅片和冶金硅粉末为原料,大量合成了Si纳米线以及多孔Si颗粒。作为锂离子电池负极材料,上述两种Si基材料由于具有纳米线形貌/多孔性质,能够缓解充放电过程中的体积膨胀,显示了优于碳材料以及Si粉体材料的充放电性能。在上述两种材料中,Si纳米线作为锂离子电池负极材料的性能更加优越。(2)以ZnO纳米棒阵列作为牺牲性模板,经共溅射的方法合成了SiGe多孔纳米棒阵列电极。作为锂电池负极材料,SiGe纳米棒阵列显示了优良的循环性能,其循环性能、倍率性能均好于平板电极以及相同方法合成的硅纳米棒阵列电极。这种多孔纳米棒阵列中存在的空隙,可以有效缓冲充放电过程的体积变化。而掺入Ge能够提高其导电性和锂离子迁移率,从而进一步提高其充放电性能。(3)利用化学气相沉积方法,在泡沫镍衬底上合成NixSiy纳米线阵列。通过共溅射的方法,在NixSiy表面沉积一层SiGe层,得到NixSiy-SiGe核壳纳米线阵列。作为锂电池负极材料,NixSiy-SiGe核壳纳米线阵列表现出了优于对应平板电极、纯硅电极以及SiGe纳米棒阵列电极的循环性能与倍率性能。这是由于NixSiy纳米线具有良好的导电性并且与电极基片具有良好的结合力,且Ge的掺入能够提高硅基材料的导电性和锂离子迁移率,因此能够进一步提高硅基材料的充放电性能。通过改变化学气相沉积过程中的SiH4与H2流量比,可以获得不同组分与形貌的NixSiy纳米线阵列。其中,Ni31Si12-SiGe核壳纳米线阵列电极的性能最为优越,这得益于Ni31Si12纳米线阵列更好的导电性以及与基片更牢固的结合力。(4)以Mg2Ge为源,在空气中热处理,经过后续酸洗,合成了多孔Ge颗粒。经乙炔裂解包碳后,得到了Ge@C多孔颗粒。这种颗粒由于具有多孔性,能够有效的缓解充放电过程中的体积膨胀,而且碳层能够提高导电性,并在充放电过程中有效缓解Ge的体积膨胀,因此能够表现出优于Ge粉体、以及商用碳材料的充放电性能。类似的方法还能被用来制备多孔Si粉等其他的多孔负极材料,提高其充放电性能。更多还原

【Abstract】 Graphite is the commercial anode material of lithium-ion (Li-ion) batteries, however, their limited gravimetric capacity (372mAh g-1) has prompted intensive research for alternative anode materials with large capacity at low potentials due to the rapid technological evolution of portable electronic devices, power tools and electric vehicles. silicon (Si) and germanium (Ge) exhibit high specific capacity and energy density, which are considered as the potential alternative anode materials for Li-ion batteries. However, the large volume changes (>300%) during the lithium insertion and extraction brings cracking and crumbling of the electrode, which results in the capacity fades and poor cycling life of the Si and Ge anode. It is believed we can be effectively improved the cycling performance by the synthesis of Si and Ge nano/mirco-structures or composites because the nano/micro-structures and the second phase in the composites can buffer the volume change during the charge/discharge process. However, much effort should be devoted to further improve the charge/discharge performance of the Si and Ge anode.In this dissertation, several Si and Ge-based nano/micro-structures have been synthesized. For example, Si nanowires and porous Si particles were synthesized by the etching of Si wafer and powder, respectively. SiGe porous nanorod arrays were synthesized by using ZnO nanorod arrays as the template. NixSiy-SiGe core-shell nanoarrays were synthesized via a chemical vapor deposition and co-sputtering method. The porous Ge particles were synthesized by thermal decomposition of Mg2Ge and acid washing. The above-mentioned materials were tested as anode materials of lithium ion batteries. The main innovative results are listed as follows:(1) Si nanowires and porous Si particles were massively synthesized by electroless etching of Si wafers and metallurgical Si powder. These two Si materials show the porous structures, thus can buffer the volume change during the charge/discharge process and lead to the improved cycling performance compared to bulk Si materials. Moreover, Si nanowires show the better performance than porous Si particles because of the1D nanostructures.(2) SiGe nanorod arrays were synthesized by using ZnO nanorod arrays as sacrificial templates via a co-sputtering method. When used as anode materials of Li-ion batteries, the SiGe nanorod arrays show the better cycling performance and higher reversible capacity than corresponding SiGe film and Si porous nanord arrays. It is believed that nanorod array structures can buffer the volume change and enhance the adhension between the nanorods and the current collector thus can show the enhanced performance. Moreover, the addition of Ge can further enhance the conductivity and improve the mobility of lithium ions, which can further enhance the charge/discharge performance.(3) NixSiy-SiGe core-shell nanowire arrays were synthesized by chemical vapor deposition and subsequent co-sputtering methods. When used as anode material of Li-ion batteries, the core-shell nanowire arrays show the better cycling performance and higher capacity than corresponding SiGe film and NixSiy-Si core-shell nanowire arrays. We believe that the core-shell nanowires own the good conductivity and good adhension with the current collector. Moreover, the addition of Ge can enhance the conductivity and improve the mobility of lithium ions, which can further enhance the charge/discharge performance.(4) Ge porous particles were synthesized by the thermal decomposition of Mg2Ge and subsequent acid washing. After the carbon coating, the as-synthesized Ge@C porous particles exhibit improved cycling performance than bulk Ge, bare Ge porous particles and carboneous materias. The porous structures and the carbon layer can buffer the volume change during the charge/discharge process, which may be responsible for the enhanced performance.更多还原