In Situ Transmission Electron Microscopy Observation of Electrochemical Sodiation of Individual Co9S8-Filled Carbon Nanotubes
In Situ Transmission Electron Microscopy Observation of Electrochemical Sodiation of Individual Co9S8-Filled Carbon Nanotubes
复制标题
单根 Co9S8 填充碳纳米管电化学钠化的原位透射电子显微镜观察
DOI：
10.1021/nn500194q
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发表时间：
2014-04-01
期刊：
影响因子：
17.1
通讯作者：
Li, Wenzhi
中科院分区：
文献类型：
--
作者：
Su, Qingmei;Du, Gaohui;Li, Wenzhi
了解钠离子电池的基本电化学行为和碱化机理是设计高性能钠离子电池电极材料的关键。本文利用原位电子显微镜直接观察和研究了单个Co9S8填充的碳纳米管的电化学固化过程和微观结构演变过程。在第一次固化时，反应前沿沿着填充的纳米线逐渐传播，导致填充的碳纳米管膨胀。填充的碳纳米管根据其结构和固化电压的大小而表现出不同的行为。对于具有开口端的Co9S8填充碳纳米管，碱化后的Co9S8填充碳纳米管的轴向延伸率为120.8%，并且由于碳纳米管壁的挤压产生了较小的径向膨胀。相反，由于碳壳的机械约束，封闭的碳纳米管表现出40.6%的较大径向膨胀和较小的轴向伸长。碱化后，由于Na+离子的插入，碳壳之间的间距从3.4埃增加到3.8埃，单晶Co9S8填料转化为分散在Na2S基质中的大量Co纳米颗粒。与碳纳米管在小充电电压下缓慢的微结构演化相比，在大充电电压下碳纳米管电极发生了强烈的电化学反应，并伴随着碳纳米管壳层的剧烈膨胀和断裂。我们的观察结果为碳纳米管复合材料在钠离子电池中的电化学过程提供了直接的证据和重要的见解。
The comprehension of fundamental electrochemical behavior and sodiation mechanism is critical for the design of high-performance electrode materials for sodium-ion (Na-ion) batteries. In this paper, the electrochemical sodiation process and microstructure evolution of individual Co9S8-filled carbon nanotubes (CNTs) have been directly visualized and studied using in situ transmission electron microscopy. Upon the first sodiation, a reaction front propagates progressively along the filling nanowire, causing the filled CNT to inflate. The filled CNTs behave differently depending on their structures and the magnitude of the sodiation voltage. For a Co9S8-filled CNT with an open end, the sodiated Co9S8 filler shows a substantial axial elongation of 120.8% and a small radial swelling due to the extrusion of CNT walls. In contrast, the closed CNT shows a major radial expansion of 40.6% and a small axial elongation because of the mechanical confinement of the carbon shells. After sodiation, the spacing between the carbon shells increases from 3.4 to 3.8 angstrom due to the Na+-ion insertion and the single-crystalline Co9S8 filler converts to numerous Co nanograins dispersed In a Na2S matrix. Compared with the gentle microstructure evolution of the CNT under small charging voltage, a strong electrochemical reaction accompanying drastic swelling and fracturing of CNT shells is observed for the CNT electrode under large charging voltage. Our observations provide direct evidence and important insights for the electrochemical process of CNT-based composite materials in Na-ion batteries.