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The international team, led by researchers at University College London, adapted an algorithm designed for investigating papyrus scrolls that are too fragile to unroll.
The ‘4D’ technique for looking inside the lithium-ion cell combined X-ray and neutron tomography to track processes deep inside during discharge. The team then used the mathematical model designed for ancient manuscripts to ‘unroll’ the electrode layers, aiding analysis and revealing that different sections of the battery were operating differently.
X-ray computed tomography allowed for the quantification of mechanical degradation effects, such as cracking from the electrode bending process during manufacturing. Imaging using neutrons yielded information about the electrochemistry, such as lithium-ion transport and consumption, or gas formation by electrolyte decay.
A new mathematical method developed at the Zuse Institute Berlin then enabled researchers to virtually unwind the battery electrodes, which are wound into the form of a compact cylinder and normally difficult to examine quantitatively.
The team found the combination of techniques provided a “fuller and more accurate” understanding of how the battery works and how, where and why it degrades over time. The researchers observed previously unseen trends in the spatial distribution of performance.
The method paves the way for strategies that could improve battery designs with different chemistries, such as better mathematical models of performance. The team, which was funded by the Faraday Institution, said the project could facilitate improvements in the range and lifetime of future electric vehicles.
"We're demanding more power from our consumer electronics all the time. To make them more efficient, and also safe, we need to understand the minor fluctuations occurring inside the batteries throughout their lifetime," said Dr. Alessandro Tengattini from the Institut Laue-Langevin (ILL) in France, which contributed its imaging techniques to the project.
"The electro-unrolling technique has enabled us to analyse the inside of batteries, while they are in use, to identify such minuscule fluctuations to almost the micrometre. It's hard to analyse lithium with X-rays because it is a lightweight element, but in combination with high-flux neutrons provided at the ILL researchers have been able to learn about the electro-chemical and mechanical properties at play simultaneously while these lithium-ion batteries are in use."
The research was published in Nature Communications.
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