Calcium-based metal-air batteries as alternative energy storage Milestone: Researchers successfully test cell design and optimised electrolytes for calcium-oxygen batteries

Climate protection and energy supply are key factors for the sustainable development of Germany as a business and technology location. In the long term, the use of fossil fuels in the energy supply must be largely avoided in order to achieve climate protection goals. Batteries with high energy density and sufficient cycle stability are essential to meet the challenges of the energy transition. In addition to solid-state batteries, metal-oxygen and metal-sulphur batteries are promising battery concepts. In the CaSaBatt research project, Technische Universität Braunschweig and its partners reached an important milestone in the development of metal-oxygen batteries in August 2024: the first cycles with the developed anode and cathode materials and electrolytes were successfully tested in a laboratory-scale test cell.

The calcium-air battery (CASB) is emerging as a promising energy storage system. It offers about 2.5 times the storage capacity of lithium-ion batteries with conventional graphite anodes and metal oxide cathodes. A few years ago, the reactions and reaction steps taking place at the anodes and cathodes in CASBs were broken down in detail for the first time. It became clear that a conventional cell design consisting of two electrodes and a porous separator, as well as a single electrolyte, could not be used for CASB. A hybrid cell design requires two different reaction chambers with anolyte (electrolyte at the anode) and catholyte (electrolyte at the cathode).

Industry and science are cooperating to develop a demonstrator

The main objective of the project described here is therefore to develop the first electrically rechargeable CASB on a laboratory scale (demonstrator). This includes liquid electrolytes (developed by IoLiTec), an ion-conducting but electrolyte-impermeable separator layer (to prevent mixing of the electrolytes; preferably realised as a solid electrolyte; developed by the University of Münster) and a chemically resistant battery casing. In addition, the best performing electrolytes (anolyte and catholyte; developed by IoLiTec) will be optimised to make the performance and cycle life of the anode (ZSW Ulm) and cathode (Fraunhofer IFAM) of the CASB competitive.

Cost-effective and suitable for upscaling

The system addressed in the CaSaBatt research project is potentially very cost-effective and also suitable for large-scale energy storage applications. With the help of an industrial partner, the electrolytes will be selected in such a way that they can be produced at low cost and are also potentially suitable for upscaling to larger scale production. Due to its fundamental nature, this project will make a significant contribution to pre-competitive research into alternative energy systems.

A basis for the next generation of batteries

The results could form the basis for the development of the next generation of rechargeable batteries for the consumer market and also in the field of low-cost, large-scale energy storage. The work described in the CaSaBatt project has a clear materials-oriented focus with a pre-industrial and partly industrial research character, in which new promising approaches for a first electrically rechargeable CASB will be developed on a laboratory scale.

Project data:

The “CaSaBatt” project (duration 01.09.2022 to 31.08.2025) is funded by the German Federal Ministry of Education and Research (BMBF) with a total of approximately 1.37 million euros (FKZ: 03XP0483A). In addition to TU Braunschweig, the project partners are the University of Münster, the Centre for Solar Energy and Hydrogen Research Baden-Württemberg (Ulm), the Fraunhofer Institute for Manufacturing Technology and Applied Materials Research (IFAM) Bremen and IoLiTec Ionic Liquids Technologies GmbH.