三维层级结构电极材料的设计、制备及应用

发布时间：2018-12-21 10:07

【摘要】：为了提高锂离子电池的能量密度和功率密度,在本文中,我们将具有纳米微米分级结构的混合导电网络引入到电极材料中。在我们的混合导电网络中,存在着大量的纳米多孔孔道,可以大大缩短锂离子的传输距离,利用这些纳米多孔孔道为基本结构单元再与微米级别的导电网络相复合,最终得到了微米级别的三维多孔导电网络,从而实现锂离子和电子的快速输运。在此基础上,我们设计了三种具有三维多孔导电网络的电极材料:首先,我们利用廉价的三聚氰胺作为碳源和氮源,乙酸钴作为催化剂,通过简单的固相烧结法,制备出了一种氮掺杂的碳纳米管和石墨烯的三维杂化结构。该结构不仅可以实现碳纳米管和石墨烯功能的互补,同时氮掺杂和碳缺陷引入的大量介孔,可以有效缩短锂离子的传输距离和存储更多的活性物质。我们还发现,该材料中金属催化剂布满整个碳骨架,与氮掺杂形成协同的催化效应。当其作为锂硫电池正极材料时,在0.5C的倍率下,循环100次后,其容量还可以保持在800mAh g-1左右,其可逆容量要远高于算出来后的样品。相对于传统的CVD法,我们的固相制备法更加安全,可操作性强,效率高,经济实用。其次,我们利用柠檬酸盐和镁粉等作为原材料,通过简单的固相镁热还原的方法制备出了具有分层多孔结构的石墨烯基气溶胶,取代了石墨烯气溶胶制备过程中最常用,但费时、昂贵的冷冻干燥法。我们制备的石墨烯基气溶胶中,具有丰富的大孔和介孔,其孔道之间以碳纳米片相互互联成三维导电网络,可以实现锂离子和电子的快速传递。当用其作为锂硫电池正极材料时,可实现超高的载硫量(75 wt%)和取得优异的电化学性能(在0.5C的倍率下,200次循环后容量保持率为54%)。最后,我们首次采用一种无定形钛基聚合物与锂盐通过简单的高温固相烧结法,得到了氮掺杂碳修饰的多孔钛酸锂材料,同时引入了具有金属导电性的TiN,成功的改善了钛酸锂电子电导和离子电导率。相对于传统的固相烧结,我们的钛酸锂材料的容量保持率提高了一个数量级,在高倍率性能也要高出一倍以上。
[Abstract]:In order to improve the energy density and power density of lithium-ion batteries, a hybrid conductive network with nano-micron hierarchical structure is introduced into the electrode materials in this paper. In our hybrid conductive network, there are a large number of nano-porous channels, which can greatly shorten the distance of lithium ion transmission, using these nano-porous channels as the basic structure unit and then composite with micron scale conductive network. Finally, a three-dimensional porous conductive network at micron level is obtained to realize the rapid transport of lithium ions and electrons. On this basis, we designed three kinds of electrode materials with three-dimensional porous conductive network. Firstly, we used cheap melamine as carbon and nitrogen source, cobalt acetate as catalyst, and a simple solid-phase sintering method. A three-dimensional hybrid structure of nitrogen-doped carbon nanotubes and graphene was prepared. The structure can not only complement the function of carbon nanotubes and graphene, but also can shorten the transport distance of lithium ions and store more active substances by introducing a large number of mesoporous nitrogen doped and carbon defects. We also found that the metal catalyst was covered with the whole carbon skeleton and formed a synergistic catalytic effect with nitrogen doping. When it is used as cathode material for lithium-sulfur battery, at the rate of 0.5C, the capacity of the battery can be kept at 800mAh g ~ (-1) after 100th cycle, and its reversible capacity is much higher than that of the calculated sample. Compared with the traditional CVD method, our solid phase preparation method is safer, more operable, more efficient and more economical and practical. Secondly, using citrate and magnesium powder as raw materials, we prepared graphene based aerosol with layered porous structure by a simple solid phase magnesium thermal reduction method, which replaced the most commonly used graphene aerosol preparation process. But time-consuming, expensive freeze-drying. The graphene based aerosols have abundant macropores and mesoporous pores and interconnect with each other as carbon nanochips to form a three-dimensional conductive network which can realize the rapid transfer of lithium ions and electrons. When it is used as cathode material for lithium-sulfur batteries, it can achieve high sulfur loading (75 wt%) and excellent electrochemical performance (capacity retention is 54% after 200 cycles at 0.5C). Finally, an amorphous titanium-based polymer and lithium salt were used for the first time to obtain a nitrogen-doped carbon modified porous lithium titanate by a simple high-temperature solid-state sintering method. At the same time, TiN, with metal conductivity was introduced. The electronic conductivity and ionic conductivity of lithium titanate were improved successfully. Compared with the traditional solid phase sintering, the capacity retention rate of our lithium titanate material is increased by one order of magnitude, and the performance of our lithium titanate material is more than twice as high as that of the conventional solid sintering material.
【学位授予单位】：合肥工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM912

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