Composites & Hybrid Materials

(images will be uploaded shortly)   Various methods of preparation are employed, such as solid state, sol-gel, and hydrothermal reactions, in order to determine which of these methods is the most effective to ultimately obtain a high-purity end product. Furthermore, physical and structural characterizations are conducted to determine the influence of the morphology, the configuration of the atoms, on the electrochemical properties. The most important starting point for this is to understand the different factors exerting an influence—based on the various underlying syntheses—on the structure, the electrochemical properties and their electrode–electrolyte interface, the properties of the surface, and possible decomposition reactions.   For this purposes, very different methods of characterization are employed, such as X-ray diffraction (XRD), inductively coupled plasma emission spectrometry (ICP-OES), and scanning electron microscopy (SEM).   Another activity of this group is the development of innovative concepts for the optimized synthesis of carbon nanocomposites or conductive layers.  

Multistep-Redox-Materials

The synthesis and characterization of so-called multistep redox materials such as lithium-metal silicates (Li2MeSiO4 ; Me=Fe, Mn, Fe/Mn)

Lithium-ion battery technology has found many applications, but it is limited by the insertion reaction that takes place with many materials and the associated transfer of at most one electron per ion of transition metal. This in turn ultimately limits the specific energy of the batteries. The reason for the interest in multistep redox materials results from the fact that these materials are capable of an insertion/extraction of more than one lithium ion per formula unit. This concept has previously only been confirmed for two-dimensional nanostructures (i.e., ultrathin film) and is now to be transferred to three-dimensional ones. To reach this goal, various approaches have been developed, such as the use of a modified sol-gel or hydrothermal approach (with the addition of a surfactant) for the synthesis of high-purity Li₂Me_xMe_(1-x)SiO₄/C composite materials (A and B).  

In situ/ex situ carbon coating of lithium metal-silicate materials

A reduction in particle size and the addition of a nanolayer of carbon is indispensible for attaining good rate and cycle stability because of the low electronic and ionic conductivity of most of the innovative electrode materials. In order to create such a nanolayer of carbon on the materials, our group developed two different processes: Regardless of the method, the addition of carbon reduces the material's energy density. Effective routes for preventing this are being examined in order to design innovative structures that contain spherical, aggregated, or compact nanocrystallites. The precise role of carbon has, moreover, not yet been completely understood and is also being studied using various analytic techniques.