Ionic Conductors

An important research field of our group is the investigation of new electrolytes, materials where electrical current is not carried by electrons but by ions. Clearly, the non-continuous nature of solar and wind energy and the future success of electromobility require significant advances in energy-storage technologies. A prerequisite is the development of better electrolytes, which are needed for modern energy storage and conversion systems such as batteries, fuel cells or supercapacitors. Achieving a thorough microscopic understanding of the motion of ions in electrolytes is essential for improving these materials.


New electrolyte materials in innovative energy-storage devices are essential for the energy supply of tomorrow. [Photos: (GraphicCompressor/petovarga/Arrows), montage: EKM/EP V]

Various strategies are pursued to achieve further advances in electrolyte technology. One is the development of better liquid electrolytes and the most prominent current examples are the so-called ionic liquids, i.e., salts that are liquid at room temperature. An alternative approach is the use of solid materials with high ionic conductivity, thus avoiding the shortcomings of many liquid electrolytes such as leakage, flammability and limited electrochemical stability. Prominent examples are amorphous polymers or ionically conducting plastic crystals.

All these material classes are thoroughly investigated by us, focusing on both basic research and their technical applicability. Dielectric spectroscopy is ideally suited for the investigation of ionic conductors. It provides valuable information on the translational hopping motion of the ionic charge carriers. Moreover, reorientational motions of molecules are also detected, which may play an important role for the ionic charge transport in various material classes.

Resistivity, Tg and fragilities of various ionic liquids

An example of our research on ionic liquids: The room-temperature resistivity of various ionic liquids is related to their different glass temperatures Tg and "fragilities" m (the latter characterizes the non-canonical temperature dependence of their resistivities). A systematic dependence on both quantities is revealed, in agreement with a model calculation (frame b): An ionic liquid should exhibit both small values of Tg and m to ensure low resistivity (i.e. high conductivity), which is prerequisite for technical applications. [Taken from P. Sippel, P. Lunkenheimer, S. Krohns, E. Thoms, and A. Loidl, Sci. Rep. 5, 13922 (2015)]

Some relevant publications from our group:

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