High-speed X-ray imaging of thermal runaway in large-format lithium-ion cells: In-situ analysis of structural failure

Thermal runaway (TR) in lithium-ion batteries remains a major safety concern, particularly for large-format cells in electric vehicles and stationary storage systems. This study presents a novel lab-based diagnostic approach that combines high-speed full-cell X-ray radiography with abuse testing to resolve the internal dynamics of a TR in real time. Synchronized X-ray imaging and external measurements (temperature, voltage, nail penetration) were applied to a 50 Ah prismatic NMC cell. The method enabled time-resolved, full-field observation of structural failure progression. The experiment revealed, for the first time in a full-scale cell, the sequence of internal events from short-circuit initiation and gas evolution to CID activation, vent obstruction, and terminal ejection. X-ray image-based analysis allowed both qualitative and quantitative assessment of material motion and gas pathways, while correlation with external sensor data established the timing of critical events. This combined method yields new insights into the mechanisms of a TR as a scalable diagnostic tool for structural failure assessment and safety evaluation of large-format lithium-ion cells. It is expected to be instrumental for the development of safer cell designs.