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

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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.