Mobility and thus also air transport cause a large CO2 footprint. In order to be able to significantly reduce this footprint in the future, light, safe and cost-effective high-energy batteries are needed. And these should, as far as possible, only contain materials that conserve resources and are environmentally compatible. A research project of the Centre for Solar Energy and Hydrogen Research Baden-Württemberg (ZSW) with three industrial companies is starting precisely here. In the project, new active materials with high specific energy and safety are being developed as well as the processes to process them into battery electrodes. Critical and expensive materials are to be substituted. Both the anode and the cathode are processed in water instead of with the harmful solvent NMP. The knowledge gained is to be used for the industrial production of round cells. The project started at the end of 2021.
In addition to the ZSW, the material manufacturer Johnson Matthey Battery Materials GmbH, the mechanical engineering company Coperion GmbH and the cell manufacturer VARTA AG are also involved. VARTA is coordinating the project, which is funded by the Federal Ministry of Education and Research (BMBF) with 1.6 million euros. The research project will run for three years until 31 October 2024.
Today, commercial high-energy cells still contain significant amounts of the expensive and carcinogenic metal cobalt, which is also sometimes mined under precarious conditions. “An important project goal will be to use cobalt-free cathode materials in future batteries by developing suitable process conditions,” says Prof. Dr. Markus Hölzle, ZSW board member and head of the Electrochemical Energy Technologies Division in Ulm. “On the anode side, the use of silicon oxide should significantly increase the energy content. Another new feature is that the production of both electrodes is water-based, i.e. without the use of the toxic solvents that are common today.”
Environmentally friendly materials with more specific energy
The consortium wants to increase the specific energy of the battery cells by up to 20 percent – compared to an already available sustainable cell chemistry. This would significantly reduce the weight of the batteries for the same energy content. This is to be achieved by four measures. First, the use of intrinsically safe lithium manganese iron phosphate (LMFP) in place of the established lithium iron phosphate (LFP) as the cathode material. Both materials are free of the critical raw materials nickel and cobalt, but LMFP contains more energy than LFP. The second measure is derived from this measure: The partners want to increase the surface capacity by 40 percent compared to an LFP cathode.
Thirdly, on the anode side, graphite, which is becoming increasingly scarce and expensive, is to be replaced by silicon oxide (SiOx), which is available in abundance. Because the energy content of SiOx is significantly higher than that of graphite, this can save weight and volume of the batteries. The fourth measure is to substitute water for the dangerous solvent NMP, which has been used almost exclusively for coating the electrodes.
Develop low-cost cell production suitable for industrial use
All improvements are to be translated into processes suitable for industrial use in order to be able to build high-performance and safe batteries on a pilot scale. To this end, the process requirements for very high-capacity electrodes – anode and cathode – during mixing, coating, drying and calendering must be investigated and understood. To this end, the scientists and engineers are researching, among other things, the process technology of extrusion as an innovative, highly efficient way of continuous processing. Based on the findings, it should ultimately be possible to produce thick water-based electrodes in an industry-relevant roll-to-roll process and wind them for use in round cells.
At the ZSW in Ulm, the processes are being tested on a dedicated pilot line and validated in small laboratory batteries as a demonstrator. In parallel, VARTA is introducing the results of the project into the production of wound button cells and 21700 round cells. The batteries developed in this way can be used in numerous applications. One important application in mobility is aviation. Battery-powered aircraft are currently being developed by various companies.
Aircraft powered by batteries are currently being developed by various companies and a high energy content with maximum safety are key factors for the success of the high-performance batteries required for this.
Coperion (www.coperion.com) is the global market and technology leader in extrusion and compounding systems, metering systems, bulk materials plants and services. Coperion develops, realizes and supports plants as well as machines and components for the plastics, chemical, pharmaceutical, food and mineral industries. Coperion employs 2,500 people worldwide in its two divisions Polymer and Strategic Markets / Aftermarket Sales and Service as well as its 30 sales and service companies. Coperion K-Tron is a brand of Coperion.
About Varta AG
VARTA AG produces and markets a comprehensive portfolio ranging from micro batteries, household batteries and energy storage systems to customer-specific battery solutions. The segment “Lithium-Ion Solutions & Microbatteries” focuses on microbatteries, lithium-ion coin power, lithium-ion round cells (lithium-ion large cells) and lithium-ion battery packs. The “Household Batteries” segment covers the battery business for end customers, including household batteries, rechargeable batteries, chargers, portable power (power banks) and lights as well as energy storage. Through intensive research and development, VARTA sets global standards and is thus a recognised innovation leader in the important growth markets of lithium-ion technology and primary hearing aid batteries. The VARTA AG Group currently employs almost 4,700 people. With five production and manufacturing facilities in Europe and Asia, as well as distribution centres in Asia, Europe and the USA, VARTA AG’s operating subsidiaries are currently active in over 75 countries worldwide.
About the ZSW
The Centre for Solar Energy and Hydrogen Research Baden-Württemberg (ZSW) is one of the leading institutes for applied research in the fields of photovoltaics, renewable fuels, battery technology and fuel cells as well as energy system analysis. Around 300 scientists, engineers and technicians are currently employed at the three ZSW locations in Stuttgart, Ulm and Widderstall. In addition, there are 100 scientific and student assistants. The ZSW is a member of the Innovationsallianz Baden-Württemberg (innBW), an association of 12 non-university, industry-related research institutes.