Electroactive Organic Molecules Immobilized onto Solid Nanoparticles as a Cathode Material for Lithium-Ion Batteries
Electroactive Organic Molecules Immobilized onto Solid Nanoparticles as a Cathode Material for Lithium-Ion Batteries
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DOI：
10.1002/anie.201001539
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发表时间：
2010-01-01
影响因子：
16.6
通讯作者：
Gaberscek, Miran
中科院分区：
文献类型：
--
作者：
Genorio, Bostjan;Pirnat, Klemen;Gaberscek, Miran
锂离子电池被认为是非常有前途的储能设备，适用于包括大型电池在内的各种应用。[1]考虑到在这种应用中需要储存大量的能量，正极材料的数量将在每电池单位千克的数量级。这不仅会引起人们对地球上一些资源的有限数量及其对环境的不容忍的担忧，还会引起对整体二氧化碳管理的担忧。[2]为了有效地克服这些问题，Armand、Chen和他的同事[2-4]最近提出了一种基于有机化合物的新型可持续锂电池。其他现有的文献主要报道了聚合物作为锂离子电池[5，6]或全有机聚合物充电电池中可能的电活性材料的使用。[7]事实上，有机分子(以及聚合物)的某些氧化还原活性中心提供了几乎无限的原子排列组合和许多取代可能性；这允许微调所需的性质。在这里，我们主要关注的是使用“单体”有机分子作为锂离子电池的活性材料。某些有机化合物的可逆容量，如LixC6O6，可高达580 mA HG±1，[3]，但它们的工作电压通常很低(约2V对Li)。然而，与电池中有机材料的利用相关的最关键的问题是许多有趣的有机分子在锂离子电池中常用的非质子电解液中的高溶解度。虽然可溶性分子可以充当电荷载体，但使用这种分子的电池的运行是有限的。此外，在长期的循环过程中使用可溶性有机分子可能是有问题的。在这里，我们首次提出，这个问题可以通过将可溶性电活性有机分子嫁接(锚定)到适当的不溶性底物表面来克服。这种方法的本质是有机分子强烈附着在合适的底物上。这种附着不仅使有机分子在电化学操作过程中保持稳定，而且还允许调节其电化学性质(例如，其氧化还原电位)。与电池不同，这种方法通常用于传感器[9，10]和超级电容器等相关领域。[11]我们通过将杯[4]芳烃(CQ)的苯醌衍生物嫁接到两种不同衬底的表面来演示这一概念：1)比表面积接近200平方米的纳米二氧化硅颗粒；1)碳黑。接枝的CQ与集电体之间的电子线路是通过进一步添加炭黑来建立的。方案1展示了一个CQ在二氧化硅纳米颗粒上接枝的假想机理和所提出的电化学反应。CQ与二氧化硅的结合性质被认为是这种有机-无机杂化体系优异的电化学稳定性的结果。选择CQ是基于已证实的对苯二酚[8]的氧化还原活性和已知的构象迁移率。[12]也就是说，虽然CQ是一个相对较大的分子，分子量为568.5 gmol±1，但它可以在底物表面调节自己，从而获得最佳的几何构型。CQ有两个对苯二酚单元，每个单元有两个氧化还原活性中心。如果所提出的四电子反应机理[13]能够完全实现，则理论容量有望达到189 mAhg？1。通过将CQ嫁接到不溶的底物上，我们不可避免地失去了这种能力的一部分。一个简单的估计表明，如果在200m2g±1的比表面积上形成CQ的单层，则总容量为39 mA HG±1(每1g…归一化
Li-ion batteries are considered very promising energy-storage devices for a variety of applications including large-scale batteries.[1] Given the large quantities of energy to be stored in such applications, the amount of cathode materials will be in the order kilograms per battery unit. This will not only raise concerns about the finite quantity of some resources on the earth and its environmental intolerance but also about overall CO2 management.[2] To overcome such problems efficiently, Armand, Chen, and co-workers [2–4] recently suggested a new class of sustainable lithium batteries based on organic compounds. The other available literature mainly reports on the use of polymers as possible electroactive materials in Liion batteries [5, 6] or totally organic polymer based rechargeable batteries.[7] Indeed, certain redox active centers of organic molecules (and also polymers) offer almost unlimited combinations of atomic arrangements and many possibilities for substitutions; this allows for fine tuning of the desired properties. Herein, our primary focus is the use of “monomer” organic molecules as an active material for Li-ion batteries. The reversible capacity of certain organic compounds, such as LixC6O6, can reach values as high as 580 mA hg À1,[3] but their operating voltage is typically quite low (about 2 V vs. Li). However, the most critical problem associated with utilization of organic materials in batteries is the high solubility of many interesting organic molecules in the aprotic electrolytes commonly used in the Li-ion batteries. Although soluble molecules can act as a charge carrier,[8] the operation of a battery using such molecules is diffusionlimited. Besides that, the use of soluble organic molecules in a long-term cycling process may be questionable. Herein we propose, for the first time, that this problem can be overcome by grafting (anchoring) of soluble electroactive organic molecules onto the surface of an appropriate insoluble substrate. The essence of this approach is the strong attachment of organic molecules to a suitable substrate. This attachment not only makes the organic molecule stable during the electrochemical operation but also allows tuning of its electrochemical properties (eg its redox potential). Unlike in batteries, such an approach is commonly used in the related fields of sensors [9, 10] and supercapacitors.[11] We demonstrate this concept by grafting a quinone derivative of calix [4] arene (CQ) onto the surface of two different substrates: 1) nanosized silica particles with a specific surface area close to 200 m2 gÀ1 and 2) carbon black. The electronic wiring between the grafted CQ and the current collector is established by further addition of carbon black. Scheme 1 shows the hypothetical mechanism of grafting of one CQ on silica nanoparticle and the proposed electrochemical reaction. The proposed binding nature of CQ onto silica is supposed to result in excellent electrochemical stability of such organic–inorganic hybrid system. The choice of CQ was based on proven redox activity of quinone [8] and on its known conformational mobility.[12] That is, although CQ is a relatively large molecule with a molecular weight of 568.5 gmolÀ1, it can accommodate itself on a substrate surface, thus acquiring an optimal geometry. CQ has two quinone units, each having two redox active sites. If the proposed four-electron reaction mechanism [13] can be fully realized, a theoretical capacity of 189 mAhgÀ1 is expected. By grafting CQ to an insoluble substrate, we inevitably lose part of this capacity. A simple estimation shows that if a monolayer of CQ on a 200 m2 gÀ1 specific surface area is formed, a total capacity of 39 mA hg À1 (normalized per 1 g …