Being able to see inside a flow battery
Being able to see inside these batteries offers new possibilities for improving them
An international collaboration – between TU/e, the Massachusetts Institute of Technology (MIT), and the Paul Scherrer Institute in Switzerland (PSI) – led by TU/e researcher Antoni Forner-Cuenca, developed this new method using neutron imaging. The breakthrough provides extraordinary moving images that help understand redox flow batteries’ inner workings.
Curiosity-driven research across disciplines
More importantly, the images provide inspiration and guidelines for new ideas and solutions. More directly, the method can aid the development of redox flow batteries, although the new imaging technique devised by Forner Cuenca’s team may also help other scientific disciplines move forward. “Our method is the result of experimenting on and borrowing from different fields. It is an exciting example of the importance of curiosity-driven research across disciplines.”
Neutron radiography plays a crucial role in the research entitled ‘Quantifying concentration distributions in redox flow batteries with neutron radiography’. Forner Cuenca learned a lot about this imaging technique during his PhD training, which started in 2013 at the PSI. Then, in 2017, he performed postdoctoral research at MIT, where he learned about redox flow batteries. That’s when the light bulb went on in his head.
“Inside the flow battery, there are moving fluids – the so-called electrolytes. An electrical current flows through the cell when the battery runs in charge or discharge. Consequently, ions and redox molecules in the electrolyte start to move in different directions, resulting in changes in the concentration of molecules. That movement determines the battery’s performance and durability, but to date, the system has remained a black box. The ability to look inside a working battery and visualize concentration distributions would enormously improve our understanding of the system.”
So, a key factor in how that battery works remained uncharted territory, which got Forner Cuenca thinking. “Our bodies are also mostly composed of fluids, namely water. X-rays pass through that and interact with heavier elements in your bones, allowing you to see them without cutting open a body. Neutrons work the opposite way: they pass through the battery casing materials easily but interact strongly with the molecules in the liquid electrolytes.”
A new application of existing science
“Using this fundamental property of neutrons interacting with certain molecules, we are using neutron radiography for the first time to look at concentrations of molecules in flow batteries.” A new application of existing science, in other words. “That technique itself is not new; it is already used by museums, for example, to see what historical objects are made of without damaging them. But now we can also use it to visualize moving fluids, as in redox flow batteries.”
The method used by Forner-Cuenca and his team is still much more laborious than X-ray photography, though, and similar to stop-motion animation. “To track in real time how the concentration of liquids changes in the battery, we continuously take pictures every 30 seconds of the collection of neutrons that travels through the battery. We piece those pictures together, so to speak, providing us with a video that shows how the concentration changes during battery operation.”
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