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Projects 2nd Phase

Hybrid Structures Derived from Phospho-olivines Type LiMPO4 with C Nanofilaments for Li-ion Batteries: Preparation, Properties and Potential Applications

PD Dr. Helmut Ehrenberg
Leibniz-Institut für Festkörper- und
Werkstoffforschung Dresden (IFW) e.V.

Prof. Dr. Wolfram Jaegermann
Technische Universität Darmstadt
Fachbereich 11 - Material- und Geowissenschaften

Prof. Dr. Jörg J. Schneider
Technische Universität Darmstadt
Eduard-Zintl-Institute of
Inorganic Chemistry &
Physical Chemistry

The continued aim of this project is to manufacture hybrid structures from lithium-containing phospho-olivines, type LiMPO4 (M=Co, Ni, Mn, Fe) with arranged carbon nanotubes (CNTs) or C nanofibres to be applied as cathode materials in Li-ion batteries. The objective is to continue to optimise the composite structures in terms of their relative dimensions and respective volume and interface properties regarding their electrical, ion-conductive and capacitive properties for application in batteries. In the second project phase, 2D structured CNT brush-like structures will be used as electronically conductive substrates alongside the commercially tested C nanofibres.
The oxidative conditioning of the C substrates with HNO3/H2SO4 will be compared using the UHV process (e.g. O-plasma) in order to understand the influence on the subsequent deposition and functional properties of CNT cathode structures. The olivines are deposited via the successful process of sol-gel synthesis from the solution or aqueous solution via deposition of precursors with subsequent ion exchange reaction to LiMPO4. Alternatively, slurry from conditioned LiMPO4 nanoparticles will be tested. This requires the identification of experimental conditions facilitating a controlled morphology of the deposited films for the application of ideal thicknesses and grain structures. The substrates from C nanofibres, the CNT brush-like structures, the resulting films and the produced composite structures will be characterised by using microscopy (REM, TEM, AFM/STM), diffraction techniques (XRD) as well as Raman and IR spectroscopy. In addition, project work will entail detailed PES and XAS investigations of the surface and interface properties of the substrates and the composite structures including the chemical composition and the electronic properties. Furthermore, by using dynamic light scattering, knowledge is to be gained about the nucleation sizes and the time flow of the nucleation of the preceramic phospho-olivine precursors. Electro-kinetic measurements (z potential examinations) are intended to obtain information about the surface charges and the polarization of the arranged CNT brush-like structures as well as about the phospho-olivine precursors. These investigations must be conducted in close cooperation with all three project groups since these results will provide an in-depth understanding of the scattering of size distribution of phospho-olivine particles as well as the decoration of the CNTs.
Finally, these findings will effectively contribute to determining the electro-chemical properties of the phospho-olivine / CNT composites. The preceramic precursors from the sol-gel suspensions of the phospho-olivines will be directly deposited into the CNT brush-like structures via flow impregnation within a micro-reactor. After calcination they will be conveyed to a self-supporting 2D CNT phosphor-olivine composite structure. The characterisation of the battery properties will be determined by means of voltage measurements with varying charge and discharge current densities and by means of impedance spectroscopy. The objective is to derive clear correlations of the nanostructure from the correlation between the battery cell sizes and the structural and spectroscopic investigations with a view to developing criteria to optimise the preparation and selection of highly promising material combinations for batteries.

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