核壳结构复合电极的设计、制备及其电化学储能特性研究

发布时间：2018-01-04 21:35

本文关键词：核壳结构复合电极的设计、制备及其电化学储能特性研究　出处：《兰州大学》2014年博士论文　论文类型：学位论文

【摘要】：锂离子电池由于具有大的能量密度、高的工作电压、长的使用寿命和可靠的安全性等优点,从众多的二次电池中脱颖而出,成为下一代安全、环保、高效电池的代表。作为实现其高效储能的基础,电极材料和电极结构的设计与制备始终是新型锂离子电池研发的热点。目前的商用石墨由于质量比容量较低(372mAhg-1),已不能满足人们对更高容量二次电池的需求。各种新型负极材料如过渡族金属氧化物、硅材料等,虽然具有远高于石墨材料的理论比容量,但本身较差的导电性以及循环过程中大的体积变化等阻碍了其实用化发展。本论文针对目前新型锂离子电池阳极普遍存在的循环稳定性较差的问题,从电极结构的设计入手,围绕核壳结构复合电极的设计、制备及其形貌、结构表征和电极特性评价等开展了系统的研究工作,旨在改善具有高比容量的电极材料的循环稳定性及其高功率输出特性。论文的主要研究内容及所获得的主要研究结果总结如下： (1)以泡沫镍为衬底,采用简单的化学气相沉积(CVD)技术生长了NiSix纳米结构阵列,比较系统地研究了生长温度、生长时间及生长气压等对NiSix形貌及结构的影响。提出了在不同气压下轴向生长与径向生长的竞争生长机理； (2)将所制备的泡沫镍支撑NiSix纳米线在空气中400℃氧化1h,制备了NiSix/NiO核壳结构纳米线阵列电极。发现在氧化包覆NiO壳层之前,对NiSi,纳米线内核进行氢氟酸溶液腐蚀处理可显著改善电极的电化学性能。200次循环后,经30min氢氟酸腐蚀并氧化处理后获得的电极的单位面积比容量高达1.28mA h cm-2,相比未经氢氟酸处理直接氧化的电极提高了3倍多。讨论了纳米线表面粗糙化所导致的电容性储锂作用对电极容量的贡献。电极循环稳定性能的改善归因于合理的核壳结构设计：导电性较好且非活性的NiSix纳米线内核可以为NiO壳层提供了有效的电子传输及稳定的力学支撑；(3)采用电感耦合等离子体CVD技术在NiSix纳米线和纳米锥阵列上沉积了非晶硅(a-Si),制备出a-Si包覆NiSix纳米线(NWs/Si)和纳米锥(NCs/Si)两种核壳结构电极。在2.1A g-1的电流密度下,NWs/Si和NCs/Si电极经50次循环后可逆比容量分别高达2650和2400mAhg-1,即使电流密度增大至8.4Ag-1,比容量仍然分别保持在1385和1220mA h g-1。显著改善的电化学性能归因于NiSix内核优良的电学和力学特性。纳米线结构在a-Si包覆过程中形成的互连网状结构也有效地改善了电极的电化学性能； (4)以泡沫镍为牺牲模板,采用CVD技术制备了质量轻、柔性好的自支撑泡沫石墨烯。以所制备的泡沫石墨烯为内核兼集流体取代了NiSix纳米结构,制备了Si薄膜包覆泡沫石墨烯(GF/Si)复合结构电极。实验发现,GF/Si电极在0.22mAcm-2的电流密度下可逆面积比容量高达1.4mAhcm-2,对应整体电极质量比容量高达620mAhg-1,与NiSix/Si核壳结构电极相比提高了约41倍。显著的电极性能改进归因于电极中引入的泡沫石墨烯：中空结构的泡沫石墨烯能够最大限度的容纳Si材料的体积膨胀,并起到反包覆活性Si材料的积极作用。
[Abstract]:Lithium ion batteries because of its high energy density, high voltage, long service life and safety of the advantages of reliable, from the two battery many talent shows itself, become the next generation of safety, environmental protection, high representative battery. As a basis for achieving the efficient storage, design and manufacture of electrode materials and the preparation of electrode structure is always a hot research model of lithium ion battery. The current commercial graphite because of lower quality than capacity (372mAhg-1), has been unable to meet the demand for higher capacity battery two times. All kinds of new anode materials such as transition metal oxide, silicon materials, although it is far higher than the theory of graphite materials the specific capacity, but the poor conductivity and circulation of large volume change is currently limited by development.
This thesis focuses on the cycle stability at present new anode of lithium ion battery is poor, starting from the design of electrode structure, focusing on the design of core-shell structure composite electrode, preparation and morphology, structure characterization and properties of electrodes were studied in engineering evaluation system, cycle stability and high power output characteristics to improve the electrode materials with high specific capacity. The main research content of the thesis and the results obtained are summarized as follows:
(1) on the foam nickel substrate by a simple chemical vapor deposition (CVD) technology. The NiSix nano array structure, systematically studied the influence of growth temperature, growth time and growth pressure on the morphology and structure of NiSix. The axial and radial growth growth under different pressures of competition growth mechanism;
(2) the preparation of nickel foam prepared supported NiSix nanowires in the air oxidation of 400 DEG C 1H, NiSix/NiO nanowires with core-shell structure array electrode was prepared. Before that, coated with NiO shells in the oxidation of NiSi nanowires, the kernel of hydrofluoric acid etching treatment can significantly improve the electrochemical performance of the electrodes after.200 cycles the unit area of the electrode, obtained by 30min and hydrofluoric acid corrosion after oxidation treatment than the capacity of up to 1.28mA h cm-2, compared with the electrode without direct oxidation of hydrofluoric acid treatment increased 3 times. The capacitive effect of nano lithium storage line surface roughening caused by the contribution to the electrode capacity. The cycle stability of electrode performance the improvement is attributed to the core-shell structure design reasonable, good electrical conductivity and non active NiSix nanowire core can provide effective electron transport and stable mechanical support for the NiO shell; (3) by inductively coupled Plasma CVD technology in NiSix nanowires and nano cone arrays were deposited on amorphous silicon (a-Si), the preparation of a-Si coated NiSix nanowires (NWs/Si) and nanotapers (NCs/Si) two kinds of core-shell structure. The electrode at a current density of 2.1A g-1, NWs/Si and NCs/Si electrode after 50 cycles the reversible the capacity was as high as 2650 and 2400mAhg-1, even if the current density increases to 8.4Ag-1, specific capacity were still keep a significant improvement in the electrochemical performance of 1220mA 1385 and H g-1. due to the electrical and mechanical properties of the NiSix kernel. Excellent interconnection network structure of nanowire structure in the process of the formation of the a-Si coating can effectively improve the electrochemical performance of electrode the;
(4) using foam nickel as sacrificial templates, prepared by the CVD technique of light quality, good flexibility of self supported foam graphene. The graphene prepared by foam as the kernel and collector instead of NiSix nanostructures, Si thin films were prepared by foam graphene (GF/Si) composite electrode. The experiment found that GF/Si electrode at a current density of 0.22mAcm-2 area than the reversible capacity up to 1.4mAhcm-2, corresponding to the overall quality of the electrode than the capacity of up to 620mAhg-1, and NiSix/Si core-shell structure compared with the electrode is increased by about 41 times. The foam graphene electrode performance significantly improved due to the introduction of the foam electrode: graphene hollow structure to maximize the capacity of Si material volume expansion, and play a positive role of anti Si activity of coating materials.

【学位授予单位】：兰州大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM912

【共引文献】