Department of Physics, Harvard University, Cambridge, MA, USA.
Department of Electrical Engineering, Howard University, Washington, DC, USA.
Nature. 2018 Jun;558(7710):425-429. doi: 10.1038/s41586-018-0205-0. Epub 2018 Jun 20.
Molecular-scale manipulation of electronic and ionic charge accumulation in materials is the backbone of electrochemical energy storage. Layered van der Waals (vdW) crystals are a diverse family of materials into which mobile ions can electrochemically intercalate into the interlamellar gaps of the host atomic lattice. The structural diversity of such materials enables the interfacial properties of composites to be optimized to improve ion intercalation for energy storage and electronic devices. However, the ability of heterolayers to modify intercalation reactions, and their role at the atomic level, are yet to be elucidated. Here we demonstrate the electrointercalation of lithium at the level of individual atomic interfaces of dissimilar vdW layers. Electrochemical devices based on vdW heterostructures of stacked hexagonal boron nitride, graphene and molybdenum dichalcogenide (MoX; X = S, Se) layers are constructed. We use transmission electron microscopy, in situ magnetoresistance and optical spectroscopy techniques, as well as low-temperature quantum magneto-oscillation measurements and ab initio calculations, to resolve the intermediate stages of lithium intercalation at heterointerfaces. The formation of vdW heterointerfaces between graphene and MoX results in a more than tenfold greater accumulation of charge in MoX when compared to MoX/MoX homointerfaces, while enforcing a more negative intercalation potential than that of bulk MoX by at least 0.5 V. Beyond energy storage, our combined experimental and computational methodology for manipulating and characterizing the electrochemical behaviour of layered systems opens new pathways to control the charge density in two-dimensional electronic and optoelectronic devices.
在材料中对电子和离子电荷积累进行分子级别的操控是电化学储能的基础。层状范德华（vdW）晶体是一个多样化的材料家族，其中的可移动离子可以电化学地嵌入到主体原子晶格的层间间隙中。这种材料的结构多样性使复合材料的界面性质可以得到优化，以改善储能和电子设备中的离子嵌入。然而，异质层改变嵌入反应的能力及其在原子水平上的作用尚未阐明。在这里，我们展示了在不同 vdW 层的单个原子界面处锂的电化学嵌入。构建了基于 vdW 异质结构的堆叠六方氮化硼、石墨烯和钼二卤化物（MoX；X = S、Se）层的电化学器件。我们使用透射电子显微镜、原位磁电阻和光谱技术以及低温量子磁振荡测量和第一性原理计算，来解析锂在异质界面嵌入的中间阶段。石墨烯和 MoX 之间形成 vdW 异质界面，与 MoX/MoX 同型界面相比，MoX 中的电荷积累增加了十倍以上，同时使嵌入势比体相 MoX 至少负 0.5 V。除了储能之外，我们用于操纵和表征层状系统电化学行为的组合实验和计算方法为控制二维电子和光电设备中的电荷密度开辟了新途径。
