Many carbon allotropes can act as host materials for reversible lithium uptake1,2, thereby laying the foundations for existing and future electrochemical energy storage. However, insight into how lithium is arranged within these hosts is difficult to obtain from a working system. For example, the use of in situ transmission electron microscopy3–5 to probe light elements (especially lithium)6,7 is severely hampered by their low scattering cross-section for impinging electrons and their susceptibility to knock-on damage8. Here we study the reversible intercalation of lithium into bilayer graphene by in situ low-voltage transmission electron microscopy, using both spherical and chromatic aberration correction9 to enhance contrast and resolution to the required levels. The microscopy is supported by electron energy-loss spectroscopy and density functional theory calculations. On their remote insertion from an electrochemical cell covering one end of the long but narrow bilayer, we observe lithium atoms to assume multi-layered close-packed order between the two carbon sheets. The lithium storage capacity associated with this superdense phase far exceeds that expected from formation of LiC6, which is the densest configuration known under normal conditions for lithium intercalation within bulk graphitic carbon10. Our findings thus point to the possible existence of distinct storage arrangements of ions in two-dimensional layered materials as compared to their bulk parent compounds.Using a double-aberration-corrected transmission electron microscope, intercalation of lithium between two graphene sheets is found to produce a dense, multilayer lithium phase, rather than the expected single layer.

中文翻译：

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两个石墨烯片之间锂的可逆超密排序

许多碳同素异形体可以作为可逆锂吸收的主体材料1,2，从而为现有和未来的电化学储能奠定基础。然而，很难从工作系统中深入了解锂在这些宿主中的排列方式。例如，使用原位透射电子显微镜 3-5 来探测轻元素（尤其是锂）6,7 受到冲击电子的低散射截面和它们对敲击损坏的敏感性 8 的严重阻碍。在这里，我们通过原位低压透射电子显微镜研究锂可逆嵌入双层石墨烯，使用球面和色差校正 9 以将对比度和分辨率提高到所需水平。显微镜得到电子能量损失光谱和密度泛函理论计算的支持。在从覆盖长而窄的双层一端的电化学电池远程插入时，我们观察到锂原子在两个碳片之间呈现多层密堆积顺序。与这种超致密相相关的锂存储容量远远超过形成 LiC6 所预期的容量，LiC6 是在块状石墨碳中嵌入锂的正常条件下已知的最致密的配置。因此，我们的研究结果表明，与其本体母体化合物相比，二维层状材料中可能存在不同的离子存储排列。 使用双像差校正透射电子显微镜，