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NEWS

December 2021 ESRFnews

Why cold batteries drain Data taken at the ESRF and the Stanford Synchrotron Radiation Lightsource (SSRL) in California, US, have given an unprecedented insight into why lithium-ion batteries lose capacity after exposure to extreme cold. The data suggest how such capacity-loss can be avoided in future technology. The performance of lithium-ion

batteries is well known to suffer at low temperatures. Part of the problem is the worsened lithium-ion transport in cold electrolytes, which has spurred the development of new electrolytes as well as the introduction of heating elements in some electric vehicles. But low temperatures can also bring irretrievable loss of capacity, due to changes in the chemistry and mechanics of battery cathodes. Now, scientists in the US and

China, with help from scientists at the ESRF, have exposed the nature and extent of these changes. At SSRL, X-ray absorption near-edge structure and extended X-ray absorption fine- structure spectroscopies performed at room temperature and at 173 °C showed how particles of standard lithium-nickel-manganese-cobalt- oxide (NMC) cathode material deform at extreme cold. Meanwhile, X-ray diffraction at various

intermediate temperatures revealed a saturation point at 73 °C, beyond which the deformations become less pronounced; and transmission X-ray microscopy showed that subzero temperatures cause cracks inside the particles, especially near to pre- existing voids. At the ESRF, nano-holotomography

at ID16A performed both at room temperature and 133 °C allowed the researchers to analyse the effect of cold on the entire electrode. The unique advantage of ID16A in this context is the possibility of reconstructing non-destructively the same large volume at room temperature and in cryogenic conditions, so that it is possible to [understand] the effect of the low- temperature exposure on the entire electrode, not just a single particle, says Federico Monaco, a postdoc at ID16A who is following up on the research. The result, he adds, is a view of heterogeneous deformations in the NMC particles within the carbon binder that lead to capacity loss (Adv. Energy Mater. 2021 2102122). The researchers speculate that the

use of NMC particles made of single crystals should minimise the initial internal voids, and thereby limit the formation of low-temperature cracks.

The unique advantage of ID16A is that it is possible to understand the effect of the low- temperature exposure on the entire electrode, not just a single particle

ID01 exposes changes in single nanoparticle

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A DESY-led research team has used the ESRF s ID01 beamline to observe, for the first time, how the chemical composition of an individual catalytic nanoparticle s surface changes during a reaction. The results will help scientists understand and improve the performance of industrial catalysts.

To make catalysts as effective as possible, scientists often maximise their surface area by making them in the form of nanoparticles. But nanoparticles can be difficult to study, especially as the changes that affect their activity occur on their surfaces.

Led by DESY scientist Thomas Keller, the team developed a technique for labelling individual platinum-rhodium alloy nanoparticles of diameter 100 nm, similar to those used in a car s catalytic converter. They took the sample to the ID01 beamline, which was not only able to image one of the nanoparticles, but also record its surface mechanical strain, which provided details of the ratio of platinum to rhodium atoms. When the sample was put under working conditions high temperatures, in an atmosphere of carbon monoxide and oxygen the rhodium content at the surface rose. This was in accordance with theory, which says that the conditions make the rhodium migrate to the surface, because it interacts more strongly with oxygen than the platinum does (Sci. Adv. 7 eabh0757).

Only by using the highly brilliant nano-focused X-ray beam available at ID01 were we able to record the diffraction pattern from a single catalyst nanoparticle of diameter 100 nm, says DESY co-author Andreas Stierle. In the future, using the EBS source, we ll be able to investigate single nanoparticles in real catalysts with dimensions in the 10 nm regime under operando conditions.

ID16A allowed the researchers to reconstruct electrodes non-destructively in extreme cold.

From blue to red, the strain field on a single nanoparticle can be reconstructed from ID01 data.

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