Researchers to build the first neutron microscope that can see inside batteries

Anyone who has had an old mobile phone or laptop has experienced that after a few years, the battery quickly runs out of power. But what actually happens inside the battery when it starts to degrade? We only know part of the answer, but now a new research project at DTU will make it possible to look directly into the battery to understand how it degrades.

Professor Luise Theil Kuhn from DTU Energy, together with DTU Physics, is leading the project, which will build a so-called neutron microscope and is funded by the Novo Nordisk Foundation.

"The challenge is that there is no good microscope for looking inside batteries. But we want to change that," says Luise Theil Kuhn.

“We have a lot of simulations of what goes on inside a battery, but it is extremely difficult to measure in 3D and in real time while it is happening. This has been a technological showstopper, but our neutron microscope will be able to confirm whether the models we have are correct,” she adds.

Neutrons form images

Neutrons are neutral particles that can penetrate materials where light and X-rays give up.

In fact, it takes two metres of concrete to stop neutrons. This means that researchers can see inside entire components – such as batteries or electrolysis cells – while they are running and without opening them up. This is crucial to understanding why materials degrade over time and how we can develop more durable and safer energy technologies.

"The neutrons are your image formers. Just as you have X-rays at the dentist that can show you what your teeth look like, here it is the neutrons that create the image that shows you what the inside of the battery cell looks like while it is running," says Luise Theil Kuhn.

Research infrastructure worth billions

In Lund, Sweden, the world's most powerful neutron source, the European Spallation Source (ESS), is being built, hosted by Denmark and Sweden. It is in this research infrastructure, which is expected to cost around DKK 17 billion, that Luise Theil Kuhn and her colleagues will install their prototype. If the project is successful, their neutron microscope will concentrate the neutron beam from ESS, making it 100 times more powerful and thus able to see details down to at least 1/50 the width of a human hair.

This is partly due to a collaboration with CHEXS, a DTU spin-out that normally makes mirrors for X-ray telescopes for NASA and ESA, but which can be adapted for a neutron microscope.

"The mirrors must be of very high quality with curved, thin metal layers. At the same time, they must be very smooth and only a few nanometres thick, so they are incredibly difficult to manufacture – virtually only CHEXS and NASA can make them," says Luise Theil Kuhn.

Once the microscope is ready, it will be able to record 3D films of how materials change in real time. These could be lithium-ion batteries used in everything from mobile phones to electric cars, but also electrolysis cells for use in Power-to-X plants.

In the longer term, the neutron microscope will be installed at ESS and made available to researchers from all over the world.

“If we can see what is happening inside the materials while they are working, we will be able to develop better batteries and more efficient electrolysis cells in the future and ultimately accelerate the green transition,” says Luise Theil Kuhn.