Vanadium oxide and vanadium sulfide/carbon hybrid electrodes by electrospinning for lithium and sodium ion batteries (HEROES-4-Li-Na-batteries)

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Our project will synthesize vanadium oxide/carbon and vanadium sulfide/carbon hybrid fibers through the combination of electrospinning and thermal treatments, and investigate their properties as electrodes for Li- and Na-ion batteries. By modifying key parameters of the hybrid material, we will establish detailed structure/property correlations. This knowledge is of high importance to establish design guidelines and synthesis strategies for future generation Li- and Na-ion battery electrodes.Most work on Li- and Na-ion batteries designs a certain Faradaic electrode material, admix a carbon conductive additive (to ensure electrical conductivity), and consolidate both components onto a current collector by use of a binder (often polymer-based). Such composites limit the understanding of the intrinsic parameters governing (and limiting) the electrochemical performance of the active components of the electrodes. Also, a more intimate, nanoscale interface between Li- or Na-ion host materials and the conductive phase can only be realized by nanoscale hybridization instead of mechanical mixing.Our work will employ electrospinning to design hybrid fibers where we obtain right away binder-free electrodes. We can use a “one-pot” synthesis approach to obtain vanadium oxide / carbon hybrids that can be converted in vanadium sulfide / carbon fibers upon H2S treatment. This approach enables a high level of nanoscale interaction between the phase where ion storage accomplishes charge storage and conductive carbon, which is superior to mechanical mixing of the two components. To achieve conductive and electrochemically stable Li- and Na-ion battery electrodes, we aim to (1) study the effect of conductive carbon content, as well as carbon character (i.e., porosity, pore size); (2) vanadium oxide/sulfide crystal structure, and (3) fiber architecture on the hybrid morphology and electrochemical properties. This will be done by combining extensive materials characterization with standard and in situ electrochemical testing.The work includes systematic analysis of the electrode materials with X-ray diffraction, electron microscopy, energy-dispersive X-ray spectroscopy, Raman and IR spectroscopy, and thermal analysis. In collaboration, we will also quantify ion diffusion und chemical states via nuclear magnetic resonance spectroscopy and complement chemical analysis via X-ray photoelectron spectroscopy. Electrochemical tests will include basic electrochemistry in organic electrolyte, rate handling, and longevity benchmarking. To further identify limiting aspects, we will employ in situ measurements to quantify structural changes by in situ X-ray diffraction, in situ electrochemical dilatometry, and electrochemical quartz crystal microbalance measurements and by use of impedance spectroscopy and galvanostatic intermittent titration technique. Structural post mortem analyses will further contribute to identify degradation mechanisms.