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Synthesis and electrochemical characterization of Silicon clathrates as anode materials for Lithium ion batteries.

机译：锂离子电池负极材料笼形硅的合成及电化学表征。

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摘要

Novel materials for Li-ion batteries is one of the principle thrust areas for current research in energy storage, more so than most, considering its widespread use in portable electronic gadgets and plug-in electric and hybrid cars. One of the major limiting factors in a Li-ion battery's energy density is the low specific capacities of the active materials in the electrodes. In the search for high-performance anode materials for Li-ion batteries, many alternatives to carbonaceous materials have been studied. Both cubic and amorphous silicon can reversibly alloy with lithium and have a theoretical capacity of 3500 mAh/g, making silicon a potential high density anode material. However, a large volume expansion of 300% occurs due to changes in the structure during lithium insertion, often leading to pulverization of the silicon. To this end, a class of silicon based cage compounds called clathrates are studied for electrochemical reactivity with lithium. Silicon-clathrates consist of silicon covalently bonded in cage structures comprised of face sharing Si20, Si24 and/or Si28 clusters with guest ions occupying the interstitial positions in the polyhedra. Prior to this, silicon clathrates have been studied primarily for their superconducting and thermoelectric properties. In this work, the synthesis and electrochemical characterization of two categories of silicon clathrates - Type-I silicon clathrate with aluminum framework substitution and barium guest ions (Ba8AlxSi46-x) and Type-II silicon clathrate with sodium guest ions (Nax Si136), are explored. The Type-I clathrate, Ba8AlxSi46-x consists of an open framework of aluminium and silicon, with barium (guest) atoms occupying the interstitial positions. X-ray diffraction studies have shown that a crystalline phase of clathrate is obtained from synthesis, which is powdered to a fine particle size to be used as the anode material in a Li-ion battery. Electrochemical measurements of these type of clathrates have shown that capacities comparable to graphite can be obtained for up to 10 cycles and lower capacities can be obtained for up to 20 cycles. Unlike bulk silicon, the clathrate structure does not undergo excessive volume change upon lithium intercalation, and therefore, the crystal structure is morphologically stable over many cycles. X-ray diffraction of the clathrate after cycling showed that crystallinity is intact, indicating that the clathrate does not collapse during reversible intercalation with lithium ions. Electrochemical potential spectroscopy obtained from the cycling data showed that there is an absence of formation of lithium-silicide, which is the product of lithium alloying with diamond cubic silicon. Type II silicon clathrate, NaxSi136, consists of silicon making up the framework structure and sodium (guest) atoms occupying the interstitial spaces. These clathrates showed very high capacities during their first intercalation cycle, in the range of 3,500 mAh/g, but then deteriorated during subsequent cycles. X-ray diffraction after one cycle showed the absence of clathrate phase and the presence of lithium-silicide, indicating the disintegration of clathrate structure. This could explain the silicon-like cycling behavior of Type II clathrates.
机译：考虑到锂离子电池在便携式电子产品以及插电式和混合动力汽车中的广泛使用，用于锂离子电池的新型材料是当前储能研究的主要重点领域之一。锂离子电池能量密度的主要限制因素之一是电极中活性材料的低比容量。在寻找用于锂离子电池的高性能负极材料时，已经研究了许多替代碳质材料的方法。立方硅和非晶硅均可与锂可逆地合金化，理论容量为3500 mAh / g，使硅成为潜在的高密度阳极材料。然而，由于锂插入过程中结构的变化，发生了300％的大体积膨胀，通常会导致硅粉化。为此，研究了一类称为笼形物的硅基笼型化合物与锂的电化学反应性。 claclasil硅由共价键合在笼状结构中的硅组成，该笼状结构由面共享Si20，Si24和/或Si28簇组成，客体离子占据了多面体的间隙位置。在此之前，主要研究了笼形硅的超导和热电特性。在这项工作中，两类硅酸盐笼形物的合成和电化学表征-具有铝骨架取代和钡客体离子的I型硅酸盐笼形物（Ba8AlxSi46-x）和具有钠客体离子的II型硅酸盐笼形物（Nax Si136）是探索。 I型包合物Ba8AlxSi46-x由铝和硅的开放框架组成，钡（客体）原子占据间隙位置。 X射线衍射研究表明，通过合成可以得到笼形物的结晶相，然后将其粉化成细颗粒，以用作锂离子电池的负极材料。这些类型的包合物的电化学测量表明，在长达10个循环中可以获得与石墨相当的容量，而在多达20个循环中可获得较低的容量。与块状硅不同，包合物结构在嵌入锂时不会发生体积变化过多，因此，该晶体结构在许多循环中形态上是稳定的。循环后，笼形物的X射线衍射表明结晶度完好无损，这表明笼形物在与锂离子的可逆嵌入过程中不会塌陷。从循环数据获得的电化学势能谱表明，没有形成锂硅化物，这是锂与金刚石立方硅合金化的产物。 II型硅包合物NaxSi136由构成框架结构的硅和占据间隙空间的钠（来宾）原子组成。这些包合物在其第一个插入循环中显示出非常高的容量，在3500 mAh / g的范围内，但随后的循环中却变差了。一个循环后的X射线衍射显示不存在笼形物相和存在硅化锂，表明笼形物结构崩解。这可以解释II型笼形物的类硅循环行为。

著录项

  • 作者

    Raghavan, Rahul.;

  • 作者单位

    Arizona State University.;

  • 授予单位 Arizona State University.;
  • 学科 Engineering General.;Alternative Energy.;Engineering Materials Science.
  • 学位 M.S.
  • 年度 2013
  • 页码 95 p.
  • 总页数 95
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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