Highlights & News
Whenever we charge our laptops at the socket or an electric car at the wall box, it is nearly always a lithium-ion battery that absorbs the power. This type of battery can currently store the most energy, while also having a small design and a low weight. If used correctly, it also retains its performance over a relatively long period. Although it has been on the market for more than 30 years, this type of battery still has a great deal of potential for development. Jülich scientists are working to further improve lithium-ion batteries to ensure that electric vehicles in future can be charged even quicker, cover longer distances, and transport greater loads.
Different applications, different requirements
Germany aims to achieve greenhouse gas neutrality by 2045. Electric vehicles play an important role in reaching the net zero target. In the transport sector, they will make an essential contribution to reducing CO2 emissions. However, batteries are not only relevant as an energy storage medium for electric cars, but also for other applications within a carbon-neutral energy system. They must be able to absorb large amounts of wind and solar power and to release the energy when required.
The electricity consumption of households and industry does not always correspond to the amount of electricity that can be generated at a given time by wind turbines or solar installations. In such instances, energy must be stored temporarily, for example using stationary energy storage systems that achieve the highest degrees of efficiency. Such stationary energy storage systems come in various sizes – from rechargeable batteries in single-family homes that draw electricity from photovoltaic modules on the roof to large factory buildings filled with batteries.
With stationary storage systems, certain aspects are often more important than those that are essential for smartphones or electric cars. Weight and volume do not play such a dominant role. Instead, there is a focus on the cost-effective production and use of the battery. It is also important that the batteries are as recyclable as possible. The raw materials used must ultimately be available in sufficient amounts and obtained in the most environmentally friendly way possible.
Alternative battery concepts
To date, lithium-ion batteries have primarily been used in stationary battery storage systems. However, given the raw materials they require and their costs, they are not actually the perfect solution. This is why Jülich researchers are conducting fundamental investigations into alternative battery types that have not yet reached the same level of technological maturity. These include solid-state batteries and metal–air batteries. The researchers are also looking at other battery types such as sodium-ion batteries and redox flow systems.
Battery types
Lithium-ion batteries are currently the benchmark when it comes to battery storage. When charging, lithium ions migrate from the positive electrode to the negative electrode, and the opposite applies when discharging. However, the material and design of the electrodes, separator, and electrolyte all vary. Jülich researchers are working on further developing these components and finding their optimal combination to improve the storage properties and safety of lithium-ion batteries.
Researchers at the Helmholtz Institute Münster (HI MS), which is affiliated to Jülich’s Institute of Energy and Climate Research (IEK-12), are focused on electrolytes. In batteries, electrolytes act as a medium for ion transport. They are also the central component with which all battery components react. The electrolytes of lithium-ion batteries often consist of complex mixtures of conducting salts, solvents, and additives. The scientists synthesize and characterize the individual components, particularly their interaction with each other and with the electrodes. Particular attention is paid to the processes at the interfaces between the electrolyte and the electrodes that are crucial to the overall performance and lifetime of a battery.
Just like HI MS, the researchers at the Fundamental Electrochemistry (IEK-9) and Materials Synthesis and Processing (IEK-1) institute divisions use conventional and innovative electrochemical and spectroscopic analysis methods for their investigations. They also create computer models to predict the properties of materials and their changes during operation.
In addition, Jülich’s Ernst Ruska-Centre offers the opportunity to investigate the atomic structure of battery materials – both fresh and used – on the smallest scale using high-resolution electron microscopes.
Solid-state batteries are viewed as the storage technology of the future. In contrast to lithium-ion batteries, they do no contain any liquid components. Their electrolyte consists of a solid. This promises a longer lifetime and a higher level of safety – no leakage and an extremely low risk of fire. In theory, solid-state batteries can also achieve better storage properties than lithium-ion batteries. In practice, however, they are still inferior.
Jülich researchers aim to change this and are particularly focused on the electrolyte. All rechargeable batteries require such a component, through which charged particles (ions) can migrate from one electrode to another. They can typically do this better in liquids than in solid materials. That is why the electrolyte is liquid in most conventional batteries.
This has a number of disadvantages, however. Metals such as lithium, for instance, react very violently with certain liquids such as water. In addition, tiny projections of metallic lithium can form in them during each charging cycle. As soon as these dendrites connect both electrodes, there is a short circuit which can lead to a fire.
The anode in lithium-ion batteries does not therefore typically consist of lithium metal, but usually of graphite, into which lithium ions can be stored. This reduces the storage capacity. Moreover, active materials dissolved in the liquid react with the electrodes, which shortens the lifetime of conventional batteries. The use of a solid electrolyte might therefore offer multiple advantages.
Ion-conducting polymers and ceramics
Jülich scientists conduct research into solid materials that conduct ions well. They are primarily focused on ceramics and polymers. Polymers are easier to produce and process than ceramics. They also react more flexibly to mechanical loads. In contrast, ceramic ion conductors can better withstand higher temperatures and are less susceptible to the influence of moisture and oxygen.
The teams at Jülich’s Institute of Energy and Climate Research that produce and characterize ceramics can mainly be found at the Materials Synthesis and Processing (IEK-1) and Microstructure and Properties of Materials (IEK-2) subinstitutes. The Helmholtz Institute Münster: Ionics in Energy Storage (IEK-12/HI MS) is instead focused on polymers.
In addition to electrolytes, the other components of solid-state batteries, such as electrodes and the separator, are researched at Forschungszentrum Jülich. Scientists from the Fundamental Electrochemistry (IEK-9) and Materials Synthesis and Processing (IEK-1) subinstitutes are trying to find the best combination of materials for solid-state batteries. They also investigate alternatives to the use of lithium for electrodes, for example sodium and silicon, which are inexpensive and available in almost unlimited quantities.
The function of metal–air batteries is based on the reaction of oxygen. However, the oxygen required for this is not found in the battery, but is taken from the air. This type of battery therefore has a high energy density in theory, i.e. a very good storage capacity with a low weight.
Jülich researchers develop, investigate, and improve metal–air batteries whose anodes are composed of pure zinc, aluminium, iron, silicon, magnesium, or lithium. A structure made of carbon or another porous material forms the cathode, which is in contact with the ambient air. The electrolyte can be solid, like in solid-state batteries, or it can be liquid. The electrolyte of the innovative titanium–air battery presented in 2023 by scientists from Forschungszentrum Jülich and the Technion – Israel Institute of Technology consists of an ionic liquid.
Extending battery lifetime
In principle, metal–air batteries are particularly suitable for applications in which a compact design is important. However, their practical application has been limited by one major difficulty: metal–air batteries can often only be charged several times before they are only able to store small amounts of energy or even stop working completely. Using analytical methods and computer simulations, Jülich researchers are helping to explain which processes are responsible for the rapid loss of function. Their aim is to suppress these processes.
Candidate for environmentally friendly large batteries
In addition to their high energy density, metal–air batteries have other crucial advantages if, for example, iron or silicon are used as the anode material: their raw materials are available in large quantities, comparatively inexpensive, and harmless to humans and the environment. They therefore appear to be particularly suitable for storing electricity in large stationary systems.
In order to store several hundred kilowatt hours of electricity, you would need a large number of litihum-ion batteries – or a single redox flow battery with two large liquid-filled tanks. Jülich researchers want to make this type of battery competitive.
A redox flow battery features two tanks, each with a liquid electrolyte, as well as two reaction chambers with one electrode each. If required, the electrolyte solutions are pumped in two separate circuits through the reaction chambers where they then absorb or release electrons at the electrodes while consuming or producing electricity. In the chambers, electricity is thus converted into energy-rich chemical compounds or vice versa.
The advantage of this construction method is that in order to expand the storage capacity of redox flow batteries, it is only necessary to increase the size of the tanks. In order to store several hundred kilowatt hours, for example, only larger tanks and more powerful pumps are required. In contrast, with litihum-ion batteries, the total number of battery cells must be increased. Redox flow technology thus promises cost advantages for large storage systems – a promise that it has not yet been able to fulfil, however.
Tuning the system
A team from the Helmholtz Institute Münster (HI MS) is researching the technology and focusing on easily accessible, environmentally friendly electrolytes. In particular, they are optimizing the monitoring and control of the redox flow system using customized sensors.
Scientists from the Institute of Energy and Climate Research – Fundamental Electrochemistry (IEK-9) are working on a special form of the redox flow battery, the iron slurry/air storage system. Together with the battery manufacturer Varta and other cooperation partners, they aim to improve the rechargeability of this battery.
Observations during operation
In order to make progress in battery research, Jülich scientists combine theory, computer simulations, and experiments. They produce new materials for various battery components and explore their potential. They also test new material combinations and battery concepts. In doing so, they use state-of-the-art analysis methods to characterize the materials and their changes during battery operation. In operando techniques play a special role and are used to observe battery components during operation on the microscopic level. These techniques are not only being put into application at Jülich but also further developed.
Role in future energy systems
A particular feature of Jülich research is that it covers the entire spectrum from basic research and materials research to systems research. Scientists at Forschungszentrum Jülich are not only advancing technological developments, but also investigating the importance of battery storage systems for the energy transition and their application in the energy system of the future. Their focus is on finding cost-efficient pathways to carbon neutrality, the optimal combination of battery and hydrogen storage media, and analyses over the entire life cycle of energy storage systems in households.
The interaction of various energy storage and conversion technologies is also investigated within the Jülich Living Lab Energy Campus. This interaction is achieved in a practical way through an intelligently networked energy supply system that is connected to the Jülich campus and integrates the various components – in a living laboratory for future energy systems.
Text: Frank Frick / Images: AI-generated symbol images, Labimage: HI MS / Judith Kraft