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.
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.
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 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.