Fransson, Matilda; (2024) Insights into Lithium-ion Battery Failure Using High-Speed X-ray Imaging. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The increasing demand for energy storage in the face of climate change has made Li-ion batteries a cornerstone of modern technology. Their application in consumer electronics, electric vehicles, and renewable energy storage depends on their high energy and power density. However, these same characteristics also introduce the risk of catastrophic failures, such as thermal runaway, where rapid, high-energy reactions can lead to explosive outcomes. This work addresses the engineering challenges of mitigating thermal runaway by deepening the understanding of this phenomenon from the material level to the cell and system levels. The research leverages advanced failure testing methods alongside cutting-edge synchrotron high-speed X-ray imaging, enabling in-situ observation of battery failure mechanisms. These imaging techniques provide unique insights into thermal runaway processes, including failure initiation, electrode layer movement, and the dynamics of molten metal formation, which are otherwise difficult to capture. Additionally, this work investigates sidewall breaches, ruptures, and cell-to-cell failure propagation, offering crucial information for the improvement of safety mechanisms in Li-ion batteries. A major technical contribution of this research is the development of a battery abuse test chamber capable of supporting high-capacity battery experiments with synchronized radiography and tomography. This chamber allows for the simultaneous collection of various types of data, advancing both imaging techniques and data processing methodologies. In one set of experiments, thermal runaway propagation in electrically connected cells is studied to evaluate the effects of series versus parallel configurations. Another study focuses on the detailed analysis of sidewall breaches observed during failure propagation, while a novel tomography technique is applied to uncover additional properties of the thermal runaway process. Ultimately, this work provides new qualitative and quantitative insights into Li-ion battery safety, using high-speed imaging and computed tomography to advance the understanding of failure dynamics. These findings lay the groundwork for future improvements in the design and safety of Li-ion battery systems.

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