Research

Lithium-ion batteries

The lithium-ion battery is currently the most important type of battery among the rechargeable high-performance batteries. While small lithium-ion batteries are already being used commercially in consumer electronics, electrical tools, hybrid vehicles, and electric cars, the commercial use of larger energy storage units is still in its early stages. The maximum storage capacity of conventional lithium-ion batteries has, however, nearly been reached. In order to achieve advances in performance, it is therefore necessary to press ahead with the development of new storage material and approaches. New electrochemical pairings and new ideas for an even more compact design are needed to achieve another significant jump in energy density.

Representative Research Field Li-Batteries

Members in Research Field Lithium-ion batteries

Post-lithium batteries

Lithium-ion and metal hydride batteries are established systems that are currently being successfully employed for energy storage in electrically powered applications. In order to make future devices safer, less expensive, more sustainable, and more powerful, researchers globally are looking for alternatives, in which lithium as charge carrier is replaced by other elements. In the CELEST research field post-lithium batteries, focus is laid on batteries using monovalent cationic (sodium, potassium), multivalent cationic (magnesium, calcium, aluminum) or anionic (chloride, fluoride) charge carriers. To realize such batteries, new functional components and materials are developed, and an understanding of the electrochemical processes is obtained. Merging concepts of organic and inorganic active materials is key to a good performance of such post-Li batteries, and organic electrode materials play an increasingly important role to enable a reversible insertion of multivalent or anionic charge carriers. CELEST partner HIU played a pioneering role in chloride-ion and fluoride-ion batteries, as well as in electrolytes for magnesium and calcium batteries. Organic electrode materials are key expertise at Ulm University, being key enablers of multivalent cell concepts.

Representative Research Field Post-Li-Batteries

Members in Research Field Post-lithium batteries

Alternative electrochemical storage and conversion devices

Fuel cells are among the enabling technologies toward a safe, reliable, and sustainable energy solution. Yet the lack of clean hydrogen sources and a sizable hydrogen infrastructure limits the fuel-cell applications today. Due to their elevated operating temperature, between 150°C and 180°C, high-temperature proton exchange membrane fuel cells (HT-PEMFCs) based on phosphoric acid doped polybenzimidazole (H3PO4/PBI) membranes can tolerate fuel contaminants such as carbon monoxide (CO) and hydrogen sulfide (H2S) without considerable performance loss. These are typical byproducts of the steam reforming process, which produces hydrogen from hydrocarbon fuels such as methanol or natural gas. So it is an appealing concept to couple a HT-PEMFC stack directly with a fuel processor, which can be used as auxiliary power units (APUs). These APUs use the fossil fuel resources more efficiently and help reduce emission of CO2. This might also be a good strategy for the wide deployment of fuel cells before the hydrogen infrastructure is established. The fuel cell system’s efficiency can be further increased by reusing the exhaust heat produced during electrical power generation.
The slow oxygen reduction reaction in concentrated phosphoric acid remains a major technological challenge for future development of HT-PEMFCs. The slow reaction rate is believed to be related to strong adsorption of phosphoric acid species on the surface of the platinum catalyst. It is generally accepted that adsorption of molecular or anionic species from the concentrated phosphoric acid electrolyte hinders ORR by blocking active sites on the catalyst surface. To gain a better understanding of the adsorption mechanisms we conduct systematic studies employing various types of perfluoroalkylated derivatives of phosphoric acid. We evaluated these model electrolytes for their adsorption behavior and influence on ORR on a polycrystalline platinum surface.

Representative Research Field Alternative Storage

Members in Research Field Alternative Storage