Li-Diffusion in oxide nanotubes and in ordered nanostructured as well as mesostructured layered materials

在过去的几年里，纳米结构材料在材料科学和能源技术领域引起了广泛的关注。在许多情况下，与粗粒度的对应物相比，它们显示出更好的性能。特别是，以界面区域体积分数增加为特征的纳米结构固体的传输或扩散参数可能与其μm尺寸的类似物显著不同。在本项目中，计划用阻抗和核磁共振波谱分别研究纳米氧化物如二氧化钛和二氧化锡(有序介孔材料，直径仅为几纳米的纳米晶，纳米片)的锂扩散和输运参数。特别是，后者提供了大量的补充技术来研究广泛的时间尺度上的微观和宏观锂动力学，包括极慢和极快的锂运动。此外，当在高温极限下测量作为频率函数的核磁共振自旋晶格驰豫速率时，它对给定扩散过程的维度很敏感。通过结构导向的溶胶凝胶法、水热法或电化学阳极氧化等方法制备的材料将通过丰富的技术组合如X射线衍射、电子显微镜、XPS、UV-Vis和高分辨率的MAS核磁共振(Li、Sn、Ti)以及使用电化学方法(循环伏安法)进行全面的表征。该项目的主要目的是研究(表面)形态、结构无序以及几何和维度对锂离子迁移率的影响。例如，在二氧化钛和二氧化锡的纳米管或纳米片中，锂的扩散可能会受到空间上的限制。因此，离子必须使用低维的迁移路径。

During the last years, nanostructured materials have attracted much attention in materials science and energy technology. In many cases, when compared to their coarse grained counterparts, they show improved properties. In particular, the transport or diffusion parameters of nanostructured solids characterized by an enhanced volume fraction of interfacial regions can be significantly different from their μm-sized analogues. In this project, Li diffusion and transport parameters, respectively, of nanostructured oxides such as TiO2 and SnO2 (ordered mesoporous materials, nanocrystallites of just a few nm diameter, nanosheets) are planned to be studied by impedance and NMR spectroscopy. In particular, the latter offers a large set of complementary techniques to study both micro- and macroscopic Li dynamics on a broad time scale including extremely slow and very fast Li motions. Moreover, NMR spin-lattice relaxation rates, when measured as a function of frequency in the high-T limit, are sensitive to the dimensionality of a given diffusion process. The materials which are intended to be prepared by, e. g., structure-directed sol-gel processes, hydrothermal methods or electrochemical anodization will be thoroughly characterized by a rich portfolio of techniques such as XRD, TEM, XPS, UV-vis and high-resolution MAS NMR (Li, Sn, Ti) as well as by using electrochemical methods (cyclo-voltammetry). The main goal of the project is to study the influence of the (surface) morphology, structural disorder and both the geometry and dimensionality on the Li mobility. For example, in nanotubes or nanosheets of TiO2 and SnO2 Li diffusion might be expected to be spatially confined. Thus, the ions have to use migration pathways of low dimensionality.