Lithium-ion batteries are the most popular battery technology today. Nevertheless, its charging properties leave space for improvement, in particular when it comes to charging speed. However, many materials that could potentially improve the properties of lithium-ion batteries in the laboratory are not sustainable because they are either rare, expensive, toxic or environmentally harmful.
High-performance storage materials based on renewable raw materials would be the ideal. During their search for a suited material, the research group from HIU and KIT came across porphyrin, an organic molecule that happens to be the basis for such substances as blood, chlorophyll and vitamin B12. During their quest, copper porphyrin, a variant of porphyrin, was provided with functional groups which, during the first charging process in the battery cell, lead to a structural and electrically conductive cross-linking of the material. As a result, the structure of the electrode in the laboratory is highly stabilized and several thousands of charging and discharging cycles become possible.
With this material, laboratory capacities of 130-170 milliampere hours per gram (mAh / g) were measured at an average voltage of 3 volts and charging and discharging times of only one minute. Current experiments indicate that the storage capacity can be increased by a further 100 mAh / g and the energy storage can be operated with the much more common element sodium instead of lithium.
“Porphyrins occur very frequently in nature and form the basic skeleton of leaf green (chlorophyll), the blood coloring substance of humans and animals (hemoglobin), or of vitamin B12,” explains Fichtner. Technical variants of such materials are already used, for example, in the blue color of laser printers or car paints. By binding functional groups to porphyrin, it has been possible to use its special properties for the first time in electrochemical storage. “The storage characteristics are exceptional because the material has a storage capacity like a battery, but works as fast as a superconductor,” summarizes Fichtner.
In the magazine “Angewandte Chemie (International Edition)”, the research group has introduced this new material system. (P. Gao, Z. Chen, Zh. Zhao-Karger, J.E. Mueller, Ch. Jung, S. Klyatskaya, O. Fuhr, M. Ruben, M. Fichtner, Porphyrin complex as self-conditioned electrode material for high performance energy storage, Angew. Chemie Int. Ed. (2017) doi:10.1002/ange.201702805)
More information: https://www.hiu-batteries.de