ABSTRACT
Tin is able to lithiate and delithiate reversibly with a high theoretical specific capacity, which makes it a promising candidate to supersede graphite as the state-of-the-art negative electrode material in lithium ion battery technology. Nevertheless, it still suffers from poor cycling stability and high irreversible capacities. In this contribution, we show the synthesis of three different nano-sized core/shell-type particles with crystalline tin cores and different amorphous surface shells consisting of SnOx and organic polymers. The spherical size and the surface shell can be tailored by adjusting the synthesis temperature and the polymer reagents in the synthesis, respectively. We determine the influence of the surface modifications with respect to the electrochemical performance and characterize the morphology, structure, and thermal properties of the nano-sized tin particles by means of high-resolution transmission electron microscopy, x-ray diffraction, and thermogravimetric analysis. The electrochemical performance is investigated by constant current charge/discharge cycling as well as cyclic voltammetry.
ABSTRACT
We present a detailed study on the exact location and dynamics of Li ions in the garnet-type material Li(5)La(3)Nb(2)O(12) employing advanced solid state NMR strategies. Applying temperature-dependent (7)Li-NMR, (6)Li-MAS-NMR, (6)Li-{(7)Li}-CPMAS-NMR, (6)Li-{(7)Li}-CPMAS-REDOR-NMR as well as 2D-(6)Li-{(7)Li}-CPMAS-Exchange-NMR spectroscopy, we were able to quantify the distribution of the Li cations among the various possible sites within the garnet-type structure and to identify intrinsic details of Li migration. The results indicate a sensitive dependence of the distribution of Li cations among the tetrahedral and octahedral sites on the temperature of the final annealing process. This distribution profoundly affects the mobility of the Li cations within the garnet-type framework structure. Extended Li mobility at ambient temperature is only possible if the majority of the Li cations is accommodated in the octahedral sites, as observed for the sample annealed at 900 degrees C. Octahedrally-coordinated Li cations could be identified as the mobile Li species, whereas the tetrahedral sites seem to act as a trap for the Li cations, rendering the tetrahedrally-coordinated Li cations immobile on the time scale of the NMR experiments.
