Researchers ‘unwind’ lithium ion battery in operation
An international team led by researchers at University College London has been able to virtually “unroll” the coils of a lithium ion battery to examine it in operation.
The team combined X-ray and neutron tomography to track the processes deep within a lithium ion battery during discharge. They then used a mathematical model designed for ancient manuscripts too sensitive to be physically opened to “unroll” the electrode layers, so aiding analysis the and revealing that different sections of the battery were operating differently.
Researchers found that using the two complementary imaging techniques and “unrolling” the electrodes while they are in normal use provides a fuller and more accurate understanding of how the battery works and how, where and why it degrades over time. Unseen trends in the spatial distribution of performance in the cells were observed.
The method paves the way for developing strategies for improving the design of cylindrical cells using a range of battery chemistries, including by informing better mathematical models of battery performance. As such the method may facilitate improvements in the range and lifetime of electric vehicles of the future.
The team investigated the processes occurring during discharge of a cylindrical commercial Lithium ion primary cell from Duracell using a combination of two highly complementary tomography methods using neutrons and X-rays. The X-rays are sensitive to heavier elements in the battery such as manganese and nickel, while the neutrons are sensitive to lighter elements – lithium and hydrogen, allowing the two techniques to visualise different parts of the battery structure and allowing researchers to build up a more complete understanding of the processes occurring deep within the cell during battery discharge.
X-ray computed tomography allowed for the quantification of mechanical degradation effects such as electrode cracking from the electrode bending process during cell manufacturing. Whereas the 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-Institut in Berlin then enabled researchers to virtually unwind the battery electrodes that are wound into the form of a compact cylinder. The cylindrical windings of the battery are difficult to examine quantitatively, and the cell cannot be unwound without inducing further damage that would not be present in an unwound battery.
The project was funded by the UK’s Faraday Institution as part of its battery degradation project.
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