The future of energy is renewable. What the exact mix of solar, wind, and hydropower will look like remains uncertain. What is clear, however, is that these energy sources must be efficiently convertible into one another. For a renewable energy mix to work, reliable storage systems are essential – and batteries and fuel cells play a central role. This is precisely where the research of Prof. Hubert Gasteiger begins. At the Chair of Technical Electrochemistry at TU Munich, he and his team investigate how batteries and fuel cells age – and how their materials can be improved. His goal: to make storage technologies fit for the energy transition.
Pushing batteries to their limits: Prof. Hubert Gasteiger’s team at the Chair of Technical Electrochemistry at the TU Munich is working at the interface between materials development and application. (Photo: TUMint Energy Research)
What are your current research priorities?
Our work focuses on new materials for batteries and electrocatalysts – in other words, for applications such as fuel cells, electrolyzers, and lithium-ion or sodium-ion batteries. We concentrate on synthesizing and characterizing these materials, particularly with regard to their aging behavior. We are especially interested in how they perform under real operating conditions. Materials are often tested in the laboratory under idealized conditions that have little to do with their later use in an actual cell. We aim to bridge that gap.
How do you test this?
We work at the interface between material development and application. For example, we use so-called single cells – small-format cells with only one pair of electrodes – to study materials for fuel cells, electrolyzers, and batteries under conditions that are as realistic as possible. This allows us to assess how well a new material would actually perform later in large multi-cell systems. We collaborate closely with the groups of Prof. Rüdiger Daub and Prof. Andreas Jossen at the TUM School of Engineering and Design.
A key objective in battery research is to achieve ever higher energy densities. What does that mean for your work?
The more energy a lithium-ion battery is designed to store, the closer one operates to the stability limits of its materials – for example, by more extensively delithiating the cathode active material in the positive electrode. This is exactly where we come in: we investigate how far this stress – that is, the degree of delithiation – can be pushed without compromising material stability. Batteries tend not only to become more susceptible to aging but potentially less safe as well, because highly delithiated cathode active material can partially decompose, especially at elevated operating temperatures. We want to understand precisely which mechanisms are involved and how materials can be specifically improved without increasing these risks.
What exactly happens during delithiation – and how is it linked to a battery’s energy density?
When a lithium-ion battery is charged, lithium ions are removed from the cathode material of the positive electrode – a process known as delithiation. The ions migrate through the lithium-ion-conducting electrolyte to the negative electrode, where lithiation takes place, while electrons travel through the external circuit. This is how energy is stored in the battery. If one aims to manufacture a battery with higher energy density – that is, to store more energy within the same volume and weight – the cathode material must be delithiated to a greater extent. The more lithium ions are extracted from the material, the more electrical charge can be stored. However, this is precisely where the challenge lies: the material becomes increasingly unstable. In short, higher energy density requires deeper delithiation – meaning the material is subjected to greater stress during charging. While this increases performance, it also accelerates aging of both the cathode active material and the battery cell and may compromise safety. We therefore investigate how far this process can be pushed without destabilizing the system – and how materials can be modified to remain stable under these demanding conditions.
How can such aging mechanisms be investigated?
We combine electrochemical methods – such as impedance measurements – with physico-chemical techniques including thermogravimetry, mass spectrometry, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy. Operando measurements are particularly valuable. During battery operation, for example, we monitor gas evolution via mass spectrometry using a setup we developed ourselves, known as Online Electrochemical Mass Spectrometry (OEMS). This allows us to draw conclusions about the underlying reactions and even determine reaction stoichiometries. To decipher the numerous aging mechanisms, specialized measurement techniques are essential. That is why we also develop our own experimental setups or adapt existing ones to suit our purposes. Such developments often take years but are worthwhile because they lead to entirely new insights.
Can you give an example?
One highlight was a study in which we demonstrated that two distinct aging processes occur in lithium-ion batteries in parallel. On the one hand, the cathode active material itself becomes unstable when highly delithiated. Oxygen is released from the material and reacts with the electrolyte, leading to decomposition of the lithium salt in the electrolyte. On the other hand, the electrolyte is oxidized at high potentials, resulting in the formation of protons that, among other effects, dissolve transition metals from the cathode active material. Using online mass spectrometry and operando X-ray absorption spectroscopy, we were able to analyze both mechanisms separately and show that they follow different patterns – for example, with respect to temperature and potential.
Collaboration certainly plays a central role in bringing new battery materials into practical application.
Absolutely. Ultimately, every new material must prove itself not only in the laboratory but also in real batteries – under the conditions that prevail in electric vehicles, stationary storage systems, or other applications. We work closely with partners at TUM to determine physicochemical data for battery management systems and to develop diagnostic methods for use in cell production. Industry partners such as BASF are also important interfaces to application. Companies often approach us with very specific questions: How does a particular material age? How can this be quantified? Which mechanisms are responsible? For such challenges, we develop tailored diagnostic methods. These collaborations are valuable for both sides – and crucial for ensuring that fundamental research finds its way into practice.
Tracking aging: Using small-format Li and Na batteries (left), hydrogen fuel cells (center), and hydrogen electrolysis cells (right), Prof. Hubert Gasteiger’s research team tests the performance and service life of electrocatalysts under realistic conditions. Targeted stress tests help to elucidate degradation mechanisms and develop approaches for improvement. (Daniel Delang / TUM)
In addition to lithium, you are also researching sodium-ion batteries. Why?
Sodium is a promising alternative to lithium, especially for stationary storage. Resources are more widely distributed globally and less expensive. However, we are still at an early stage, and many fundamental questions remain open. The chemical toolbox is much broader, which makes the field exciting but also more complex. We are currently involved in a major collaborative project funded by the German Federal Ministry of Education and Research: Sodium-Ion-Battery Deutschland-Forschung (SIB:DE). The overarching goal of the initiative is to establish a comprehensive ecosystem for sodium-ion battery production. Our role in the project is to adapt diagnostic methods developed for lithium-ion batteries so that aging mechanisms in sodium-ion batteries can also be elucidated.
“Batteries remain a ‘black box’—many things work without us understanding exactly why. That’s what makes research so exciting and motivating,” says Prof. Hubert Gasteiger. (Photo: V. Hiendl/e-conversion)
Let’s turn to fuel cells. What makes research in this area particularly challenging?
Unlike battery research – where the relatively simple test setups allow hundreds, and in industry even tens of thousands, of parallel measurements to study cell aging – aging tests for fuel cells are highly demanding. The experimental systems are far more complex and expensive. They require not only more laboratory space but also sophisticated technical infrastructure. In addition, the testing environment is elaborate: hydrogen and oxygen must be precisely supplied, the gases humidified, pressure and temperature kept constant, and the cell carefully conditioned throughout the entire runtime. Even large companies can typically operate only a few dozen test stations – and university groups often far fewer than ten. Since a single aging test on a fuel cell can take weeks or even months, validating a new catalyst or other component requires significant time and resources to obtain statistically meaningful results. Careful planning and targeted parameter selection are therefore essential.
Are there strategies to make testing more efficient?
One approach involves so-called Accelerated Stress Tests. In these tests, the cell is deliberately exposed over extended periods to specific stress factors, such as strongly fluctuating voltages, high temperatures, or demanding operating cycles. The aim is to make typical aging processes visible within a shorter timeframe – processes that would otherwise only appear after years of real-world operation. Such tests provide important insights into how and why fuel cells age – and how materials and operating strategies can be improved to extend their lifetime.
What particularly motivates you in your research?
Our findings help improve real-world applications. Fuel cell testing requires considerable effort and planning and is scientifically demanding, but also highly rewarding – especially when it reveals mechanisms that remain hidden under normal operating conditions. Moreover, the insights we gain into the influence of individual materials, components, and operating strategies on performance and aging can also be used to advance the development of powerful and durable water electrolyzers. Batteries, too, remain in many ways a “black box” – much works without us fully understanding why. That makes the research both exciting and motivating. And I take great pleasure in working with so many dedicated and intellectually curious young researchers, watching them grow within their field – and often beyond it – from learners into critical discussion partners who develop new, impressively creative ideas and solutions.