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Project CaSino investigating calcium-sulfur batteries

The joint European project “CaSino” is investigating the potential of the calcium sulfur (Ca-S) battery as an alternative to lithium-ion batteries. The project consortium consists of five research institutions, two industrial companies and an industrial advisory board and is coordinated by DLR Stuttgart. It is funded with €3 million by the German Federal Ministry of Education and Research (BMBF).

Lithium is a stellar element for an electrochemical cell in many ways—it combines a high power storage capacity and cell voltage with fast ion migration. This enables compact batteries and fast loading and discharging.

However, lithium-based systems have an increased risk of fire, as dendrites can form with repeated charging, which in the worst case lead to an internal short circuit. In addition, the lithium deposits on earth are limited and not available on all continents, mining is controversial and it can only be recycled extensively.

Calcium—a multivalent metal like aluminum, magnesium and zinc—is 400 times more common and therefore inexpensive, as well as worldwide and equally distributed. Like lithium, it has a high storage capacity and cell voltage and is also safer in terms of short circuits, as calcium does not form typical dendrites in operation.

The biggest challenge when using calcium is its reactivity and formation of surface layers, whether in contact with air or moisture, or even with the electrolyte used in the battery. The oxidized surfaces later block ion diffusion and thus prevent efficient loading and unloading. The development of a compatible electrolyte thus plays a key role. In addition, soluble polysulfides are generated when using a sulfur cathode, which can also block the Ca anode.

The CaSino project has now set itself the goal of achieving significant progress in terms of cycle stability and energy density of calcium sulfur batteries through innovative material development. These steps are accompanied by experimental investigations, advanced analysis methods and extensive modeling work. The BMBF-funded joint project is coordinated by the Institute of Technical Thermodynamics of the German Aerospace Center in Stuttgart during the three-year project duration.

From the consortium, the Karlsruhe Institute of Technology (KIT) and its Helmholtz Institute Ulm (HIU) play a pioneering role in the field of research on calcium batteries. With a non-corrosive boron-based electrolyte, KIT has laid the foundation for the further investigation of Ca batteries. This recent development now allows a more stable loading and discharge of Ca batteries over hundreds of cycles. Based on this, KIT, together with IoLiTec GmbH, the specialist for ionic liquids, aims to further improve the already established KIT electrolyte.

The Research Institute for Precious Metals and Metal Chemistry (fem) addresses the need for thin and structured Ca anodes, while the DLR Institute of Technical Thermodynamics develops tailor-made coatings to protect against passivation.

The electrochemical characterization of the new materials will be extended by innovative structural and morphological analysis methods (analytical electron and ion microscopy) at the Institute of Natural Sciences and Medicine (NMI) at the University of Tübingen. Furthermore, the experimental activities are supported by atomistic simulations at the University of Ulm as well as continuum simulations and modeling of the Ca-S cell at the DLR Institute of Technical Thermodynamics.

Finally, a comprehensive consideration of economic and ecological aspects by EurA AG should highlight the potential of the Ca-S system in terms of sustainability, costs and recyclability compared to state-of-the-art battery materials.

The project will continue to be accompanied by an industry advisory board consisting of the companies Alantum, Varta, CustomCells and Accurec. All integrated institutions and companies work together towards the goal of demonstrating the performance of this sustainable energy storage technology based on calcium and sulfur in an industry-compatible battery cell for use as stationary storage.

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