Meaning
Non-destructive imaging procedure that captures the three-dimensional internal structure of a battery cell while it remains under active test conditions or during a charging cycle. Utilizing in situ micro ct provides researchers with a way to observe physical changes inside the cell without disassembling it, which would disturb the internal environment. This technique uses X-ray tomography to generate high-resolution images of the electrodes, the separator, and the electrolyte distribution at different states of charge.
The data collected is used to understand how the microstructural features of the cell evolve over time and how they contribute to the overall performance and degradation.
Tomographic Resolution
Quality of the captured images depends on the intensity of the X-ray source and the precision of the detection equipment. High-resolution in situ micro ct can reveal features as small as a few hundred nanometers, allowing for the visualization of individual active material particles and the pore networks between them. These images are reconstructed into a three-dimensional model that can be rotated and sliced to examine the internal volume from any angle.
Because the cell is imaged while it is operating, researchers can see how the particles expand and contract as lithium ions move in and out. This level of detail is necessary for identifying the start of structural failures like particle cracking or electrode delamination.
Active Morphology
Shape and arrangement of the materials inside the battery change as the cell is cycled, often leading to a loss of contact between the active particles and the current collector. By performing in situ micro ct during a discharge event, scientists can identify which parts of the electrode are contributing to the current and which parts have become inactive. This information is used to improve the design of the electrode slurry and the coating process to ensure a more uniform distribution of materials.
The technique also shows how the liquid electrolyte moves through the pores and if any dry spots or gas bubbles are forming. These observations are fundamental for developing batteries with higher power densities and longer cycle lives.
Degradation Visualization
Long-term aging of a battery often manifests as physical changes that are clearly visible in the tomographic scans. In situ micro ct allows for the tracking of lithium dendrite growth, which is a major safety concern that can lead to internal short circuits and thermal runaway. Seeing these dendrites as they form provides valuable data for testing the effectiveness of new separator materials or electrolyte additives.
The technique is also used to study the effects of mechanical abuse, such as how the internal structure deforms when the cell is subjected to external pressure or impact. These insights are shared with safety engineers to help them design more robust battery packs for electric vehicles and grid storage systems.
