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Methods

Research in the Methods field is concentrated on the development and targeted use of selected techniques of analysis in order to make visible the reaction pathways and atomic phenomena of electrode materials and cells. Detailed knowledge about the processes taking place during charging and discharging are necessary to guarantee a long lifespan and safe operation of a battery. This can only be acquired by using special methods of examination, which are further developed as needed. Both fully functional research cells and commercially available battery systems are analyzed. The scientists employ sensitive methods of analysis to study atomic processes, in part in real time directly during the process of charging or discharging. By looking inside the battery—without disturbing its functioning—it is possible to recognize modifications of the material as a result of fatigue and aging and to precisely observe the mechanisms causing the damage. On the basis of this information, the scientists at HIU can prepare dedicated recommendations for the development of material for higher performance and safer energy storage units.

Microscopy

A prime task of microscopy is to examine materials in a highly precise manner and to observe their modification by various factors in real time. Light microscopy is employed to examine materials inside the electrolyte in real time. It alone offers the possibility of observing processes in real time in realistic surroundings. The technique is used, for example, to study lithium deposition under conditions comparable to those in real cells.

The scanning electron microscope is a versatile tool for studying materials at a high resolution. For battery materials, the focus is on materials sensitive to air that can be transferred using a special transfer system.

Transmission Electron Microscopy

Transmission electron microscopy is used by all research groups and disciplines. It contributes to the observation of active battery materials at a resolution in the atomic to nanoscale range. This is possible in both two and three dimensions. It produces high-resolution data containing information of a structural, morphologic, chemical and/or spectroscopic nature about the material. The modification of material such as during charging or discharging can, as a result, be determined in both structural and spatial resolution.

Spectroscopy

Spectroscopic methods utilize the absorption or scatter of electromagnetic waves—which include those of light—to draw inferences about the structure of the materials being studied. Among the spectroscopic methods employed at HIU are nuclear magnetic resonance (NMR), Mössbauer spectroscopy, and Raman scattering.

Diffraction

X-ray diffraction studies are conducted at HIU on a synchrotron as well as using laboratory diffractometers, for which a powerful version especially designed for battery research is also employed. Identification of the structures is possible using this technology, and phase transformations can be studied in detail during lithiation and delithiation. In experiments using the synchrotron and conducted in collaboration with other research groups at HIU, in situ and ex situ measurements of x-ray diffraction and x-ray absorption are carried out in order to study the structure of electrode materials. The strong interaction and the scattering cross-section of the thermal neutrons with lithium and oxygen make neutron radiation an ideal probe for battery materials. By using neutron diffraction, it is possible to monitor the crystal structure of the anode and cathode materials. Structural change can thus be studied during charging and discharging, just as it can be determined during a battery's aging.

 

 

Mechanical Measurements

Mechanical tension is formed in electrode materials during the storage and removal of lithium. Since this stress can lead to damage, measurement of the stress is helpful in assessing the reliability of material. An effective means to conduct such experiments is the substrate curvature method, in which a thin film is observed on a carrier, in this case the substrate. If the film undergoes mechanical tension, the electrode film–substrate system curves slightly. By measuring the substrate curvature, the tension in the electrode film can be calculated. At HIU it is uniquely possible to conduct such measurements on the basis of composite electrodes such as used in real batteries.