Smartphones and laptops constantly in use, smart building technology, the expansion of renewable energies, networked charging stations for electric cars or the debate surrounding air taxis: sustainable, safe and efficient batteries are the basis of our lives as well as paving the way for the future. In honour of the useful daily helper, the USA created the National Battery Day, which takes place annually on February 18- the birthday of the Italian physicist and inventor of the battery: Alessandro Giuseppe Antonio Anastasio Count of Volta. What are the future developments in the field of electrochemical energy storage? A comment by Martin Winter, scientific leader of MEET Battery Research Center of the University of Münster and Helmholtz Institute Münster of Forschungszentrum Jülich.
Lithium-ion batteries currently dominate the market. They combine high performance and energy density with a long life cycle, safety and lowest costs. These are the factors that - as a whole - determine the marketability of a battery. With sustainability, another parameter has been added in recent years. Sustainability is shaping battery research today and will influence its future even more decisively. In order to cover all these factors, battery research must pursue three complementary research fields simultaneously.
Coherence of Three Research Fields
Research and development on the lithium-ion battery plays a decisive role throughout the entire value-added cycle, from materials to cell production and recycling. Optimising them and, at the same time, substituting critical raw materials such as cobalt and nickel are among the most important goals in this field. The approach of replacing critical materials with sustainable, resource-friendly raw materials is an growingly important topic in the battery community. However, transition metals such as manganese and iron, which could replace cobalt and nickel, are currently still facing several challenges: their energy density is lower, their stability is quickly compromised and they are at least in part more soluble in the electrolyte- all these factors lead to side reactions in the battery that affect its performance, lifetime and safety. Further intensive research on new material concepts for the lithium-ion battery, therefore, is all the more important.
When changing materials, it is crucial to consider whether the energy consumption really improves the sustainability of the battery. Simply expressed: If a kilogram of lithium-ion battery achieves an output of 300 watt-hours, but a kilogram of a battery system with other materials only achieves an output of 100 watt-hours, more material is needed and must be paid. Additionally, other factors such as transport and production costs rise. In turn, this has a negative impact on the CO2 balance of the battery. Comparisons of battery systems should therefore always be made with a view to the command variable of kilowatt hours.
The second field addresses the development of high-energy density batteries. It focuses on lithium metal batteries, especially with solid electrolyte and/or with sulphur cathode. Since the lithium metal battery promises higher energy contents than the lithium ion technology, it is a particularly interesting candidate for use in electromobility, where long ranges are required. At present, however, it still struggles with safety deficiencies. Holistic research is essential to overcome the weaknesses of rechargeable lithium metal batteries.
Still anchored in basic research is the third, forward-looking field: research and development on lithium-free battery systems. An exception is the sodium-ion battery, which has not reached the level of the lithium-ion battery in terms of cost and performance yet. Therefore, breakthroughs must first be achieved in materials research and in laboratory cells before further steps, such as production research, can be initiated.
Circular Value Added: Battery Recycling as Key Topic
Across all these research approaches, recycling must and will play an important role. A circular value added in battery research and production can only be considered this way. The use of recycled materials not only reduces the cost of the initial raw materials, but also enables energy reductions in battery production. By shredding, burning and treating batteries with acid so far, not only the necessary separation of the materials is missing, but also their degree of purity is insufficient to reuse them in batteries. Research into battery designs that enable more efficient recycling, for example by simplifying the disassembly of the cells, will therefore gain relevance in the future - in conjunction with the development of corresponding process steps.
Broad Research, Focused Production
While a broad range of battery chemistries is being analysed in research today as well as tomorrow, production has to focus on only a few technologies - for several reasons: Firstly, a new battery system can only be mass-produced once it has been intensively researched on a pilot scale and has reached its Technology Readiness Level (TRL). Secondly, each new battery technology requires its own infrastructure. Lithium-ion battery production processes can only be transferred to new systems on a very limited degree. Therefore, the switch to so-called post-lithium-ion batteries with new process technologies, manufacturing environments and skills would require billion-dollar investments. Focused production also benefits from scale effects and cost reductions. The fundamental condition is that the battery can be used for different applications.
Overall, Germany has started an enormous race to catch up in battery research over the past 15 years, which is still continuing today - and there is a strong need because the competition never stops. The combined funding of regional competence centres and national joint projects from industry and academia guarantee that Germany has positioned itself among the strongest research nations in the world. Expanding this status by intensively pursuing the three research fields in parallel and focusing strongly on battery recycling across all approaches will dominate the future of battery research.