'Thermal runaway' in lithium-ion cells is typically triggered by internal short circuits, overcharging, or external factors such as excessive heat or physical damage. It initiates a chain reaction of exothermic processes, causing rapid temperature escalation, gas release, and the potential violent rupture or combustion of the cell.
Challenges in Investigating Thermal Runaway:
Thermal runaway is a highly dynamic process that unfolds within milliseconds, making it challenging to capture and analyze its intricacies using conventional imaging techniques. Traditional methods like thermocouples or infrared cameras offer limited temporal and spatial resolution, leaving gaps in our understanding of the complex thermal and mechanical phenomena associated with thermal runaway.
High-Speed Tomography:
High-speed tomography is an advanced imaging technique that combines high temporal resolution with three-dimensional imaging capabilities. It provides researchers with a comprehensive view of the internal changes occurring within a lithium-ion cell during thermal runaway, enabling a deeper understanding of the underlying processes.
Working Principle of High-Speed Tomography:
High-speed tomography involves the use of X-ray imaging systems capable of capturing rapid sequences of two-dimensional cross-sectional images. By acquiring images at extremely short time intervals, typically in the microsecond range, researchers can reconstruct three-dimensional representations of the evolving internal structure of the cell during thermal runaway.
Benefits of High-Speed Tomography for Thermal Runaway Analysis:
Real-time Visualization: High-speed tomography allows researchers to observe the thermal runaway process in real-time, capturing critical stages of cell failure and identifying contributing factors.
Spatial Resolution: The technique provides high-resolution images, enabling researchers to analyze internal changes such as gas evolution, morphological deformations, and electrolyte distribution within the cell.
Quantitative Analysis: High-speed tomography enables the extraction of quantitative data, such as temperature distribution, volumetric expansion, and gas volume fraction, facilitating the development of accurate computational models for predicting and mitigating thermal runaway.
Comparative Studies: By examining multiple cells simultaneously, high-speed tomography allows researchers to conduct comparative studies, investigating the impact of different cell designs, materials, or operating conditions on the occurrence and propagation of thermal runaway.