Solid State Batteries

Solid-state batteries offer enhanced energy densities and a high level of safety and reliability. The Fraunhofer BatteryCampus focuses on developing components such as electrolyte-separators and composite electrodes for advanced next-generation cell chemistries. This includes various active species such as lithium, sodium or aluminum, as well as different material classes such as sulfides, oxides or phosphates.

Some materials are developed in-house at Fraunhofer, while others are commercially available or provided by partners. Additionally, suitable processes for assembling cells from their individual components, interactions between components, and surface reactions are investigated.

Sulfidic solid-state electrolytes enable increased safety and an increase in energy density through the use of high energy anodes. Challenges exist at the mechanically/chemically unstable interfaces and in processing electrodes and cells. At Fraunhofer IWS, innovative material and process approaches to solving these major challenges are being developed and demonstrated in prototype cells. Material innovations include carbon and silicon anodes that enable operation at room temperature without dendrite formation, as demonstrated by initial investigations on pouch cells. Process innovations include dry coating of electrodes and solid electrolyte membranes as well as Lithium and Silicon thin film anode deposition. A research focus of Fraunhofer IKTS is the development of suitable processing methods and rapid characterization techniques. The developed components are evaluated to better understand the relationship between performance and material properties, allowing for specific material improvement and cell concept optimization. For this, crystal and particle properties must be precisely tailored to the needs of the final composite, enabling the adjustment of electrochemical properties to meet the required characteristics of the solid-state cell.

A focus at Fraunhofer IKTS is the development of materials and processes for electrolytes and composite cathodes of lithium or sodium solid-state batteries. Both materials developed at Fraunhofer IKTS and commercial materials are tested using electrochemical methods for their application in solid-state batteries. Additionally, methods for cell assembly, interactions between components, and interfacial reactions are investigated. Integrated systems comprising multiple gloveboxes and a dry room are available for the production of test cells.

The Fraunhofer IKTS develops sodium-based high-temperature batteries for stationary energy storage from the material to the fully functional battery system. The main focus of development is on Na/NiCl2 and Na/S battery systems, both of which are based on the solid-state electrolyte Na-β"-aluminate. The idea is to “redevelop” Na/NiCl₂ and Na/S batteries with the proviso that cells and systems are produced as cost-efficiently as possible. For this purpose, the cell and system design, the materials and the production technologies are under investigation. A pilot production for solid electrolytes, cathode material and cells will enable all the necessary process steps to be scaled up close to the industrial application.

Lithium-sulfur batteries (Li-S) are characterized by high specific energy (currently up to 450 Wh/kg) and potentially low material costs. The complex cell chemistry requires further development of cell components and their coordination with each other. Fraunhofer IWS has developed and patented numerous concepts for this purpose. Lithium metal anodes are manufactured, modified and automatically processed in cell assembly. Solid state electrolytes can enable increased energy density. The developments are demonstrated in prototype cells with up to 25 Ah capacity and tested with application-relevant protocols.

The rechargeable aluminum-ion battery (AIB) is a cost-effective and non-flammable electrical storage system. As a high-power storage, the AIB can be loaded and unloaded in less than 20 seconds. The process is reversible for more than 10000 cycles in lab test cells at Fraunhofer IISB, exhibiting >95 % Coulomb efficiency and more than 85 % energy efficiency. We manufacture single and multi-layer AIB pouch cells with a capacity of up to 200 mAh, which achieve more than 1000 cycles at charging rates between 6 and 10C. AIBs have a high potential for stationary and hybrid mobile applications, e.g., for grid stabilization or uninterruptible power supply (UPS).

Fraunhofer IKTS conducts post-mortem analyses of battery cells to uncover degradation mechanisms. Cells up to 500 Ah are opened in a glovebox under inert atmosphere. CT scans are performed in advance. During the opening, processes and irregularities are recorded, and samples are taken for material analyses. Using imaging and analytical methods, we analyze the cell components. Extracted electrodes are electrochemically characterized to investigate degradation effects. As a service provider in Germany, we are available to international partners.

Fraunhofer IISB has comprehensive analytic and characterization tools, used for in-depth examinations of new materials and processes. Focusing on structural characterization via X-ray diffraction (XRD) and Raman spectroscopy, operando investigations allow to analyze structural changes in battery cells or battery components during charge or discharge. The resulting large amounts of data are evaluated with AI routines. The thus enabled profound understanding of underlying chemical processes and failures mechanisms forms the basis of designing new battery materials by unravelling structure-property relations.