Conventional methods such as X-rays, CT or MRI allow us to see parts of the interior of bodies and objects without opening them. These extraordinary advances have a limitation: the fluids and the behavior of the chemical elements that compose them over time are invisible. An investigation directed by the Spanish Antoni Forner-Cuencaprofessor of electrochemical materials and systems at the Eindhoven University of Technology (Netherlands) after studying at MIT (Massachusetts Institute of Technology), has managed to jump that barrier. Using neutron x-rays he has revealed the composition and behavior of the internal elements in a working battery. It cannot be used on living organisms due to the effect of radiation, but it is a door to the invisible world that collects Nature Communications.
The International Atomic Energy Agency (IAEA, for its acronym in English), defines “neutron imaging” as a non-destructive technique to analyze the structure of a sample from a beam of neutrons that passes through it and is attenuated according to its composition and shape. The results it provides are fundamental for electrochemical analyzes of fuel cells, the study of the dynamic efficiency and performance of batteries or motors, quality control in the automotive, aviation and construction industries, the non-invasive study of heritage objects cultural and biological samples, geology, nuclear fuel examination or materials research.
The investigation of Forner-Cuenca and his team has gone one step further and, as the Spanish researcher explains, has developed and demonstrated in a flow battery an imaging method with neutrons to visualize concentrations in liquids and their behavior.
“In a battery, there are a series of processes that occur inside that determine its performance, efficiency and useful life. Until now it was a black box. Voltage and electrical current could be measured, but what was happening inside was unknown. With our method we can take photos and videos of these processes during the operation of the battery and see how the concentrations change within the electrochemical cell,” he explains.
The magicians who reveal the hitherto invisible are neutrons, subatomic particles with no net charge and which, due to this characteristic, do not interact with electronic clouds. The neutron passes through the external structure of the object as if it were transparent, but is attenuated when encountering molecules containing hydrogen or boron.
The industrial application is evident, especially to improve the efficiency of the flow batteries analyzed, which are key for energy from renewable sources due to their large-scale and long-life storage capacity. “I see applications in various processes in the chemical industry – where there are conversions of molecules in the liquid phase – or to understand how prototypes work,” adds Forner-Cuenca.
The images of spaces that were invisible have revealed the movements of the molecules, how they fluctuate in the loading or unloading phases, the most inactive areas or the precipitation of solids. All this information allows us to design more efficient batteries.
“The research has been led by the Spanish researcher Forner-Cuenca and his team (Maxime van der Heijden, Remy R. Jacquemond, and Emre B. Boz) at the Eindhoven University of Technology, in collaboration with MIT and the Paul Institute Scherrer of Switzerland (PSI), which provided the facilities for the development of the experiments, which lasted for 12 days uninterruptedly and with measurements every 30 seconds.
The line of work of the European university is shared by other international entities because, as explained by Santanu Roy, co-author of a research published in Journal of the American Chemical Society, “A better ability to predict and calculate microscopic behaviors, as well as obtaining reliable data, helps to develop better models.”
The scientist, who researches molten salts as reactor fuel and coolant, explains that “the chemical, structural and dynamic behavior of salts at the atomic level is difficult to understand.” When a beam of neutrons is directed at a sample, many of them pass through the material, but some interact directly with the atomic nuclei and “bounce” at an angle, like colliding balls in a game of pool. Using special detectors, scientists count the scattered neutrons, measure their energies and the angles at which they scatter, and map their final positions. This makes it possible to obtain details about the nature of materials, from liquid crystals to superconducting ceramics, from proteins to plastics, and from metals to metallic glass magnets.
Also in line with improving device performance, Osaka University (Japan) has used neutrons to measure internal temperatures of electronic components quickly and accurately. The method, also published by Nature Communications uses a technique called “neutron resonance absorption” to examine neutrons absorbed by atomic nuclei at certain energy levels and deduce material properties. “This technology allows temperature to be measured instantaneously (100 nanoseconds) and, as it is non-destructive, it can be used to monitor devices such as batteries and semiconductor devices.” explains Zechen Lan, lead author of the work.
