Abstract
This paper presents the non-uniform change in cell thickness of cylindrical Lithium (Li)-ion cells due to the change of State of Charge (SoC). Using optical measurement methods, with the aid of a laser light band micrometer, the expansion and contraction are determined over a complete charge and discharge cycle. The cell is rotated around its own axis by an angle of α=10° in each step, so that the different positions can be compared with each other over the circumference. The experimental data show that, contrary to the assumption based on the physical properties of electrode growth due to lithium intercalation in the graphite, the cell does not expand uniformly. Depending on the position and orientation of the cell coil, there are different zones of expansion and contraction. In order to confirm the non-uniform expansion around the circumference of the cell in 3D, X-ray computed tomography (CT) scans of the cells are performed at low and at high SoC. Comparison of the high resolution 3D reconstructed volumes clearly visualizes a sinusoidal pattern for non-uniform expansion. From the 3D volume, it can be confirmed that the thickness variation does not vary significantly over the height of the battery cell due to the observed mechanisms. However, a slight decrease in the volume change towards the poles of the battery cells due to the higher stiffness can be monitored.
Highlights
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The battery cell has a positive electrode made of nickelrich Nickel Cobalt Manganese Oxide (NCM) active material and a negative electrode made of graphite
Where the negative current collector tab is located, the cell expands at an above-average rate, while it contracts more than average at points where the jelly roll is not directly against the housing and a cavity is created
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The mechanical properties of commercial Li-ion cells are increasingly coming into focus, especially considering the steadily growing requirements. Higher energy and power densities, less space consumption, and longer service life—these are the challenges that need to be overcome. Many promising material combinations are limited by their mechanical properties or are not suitable for real applications. Silicon has a significantly higher energy density and specific capacity (QSi = 4200 mAh g−1 [1])
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