Work

Trajectory analysis of ejected particles during thermal runaway of large-format lithium-ion cells

Year: 2026

Type: article

Abstract: Thermal runaway (TR) in lithium-ion batteries is accompanied by rapid gas release and particle ejection, both of which present significant safety hazards. This work investigates the particle dynamics of TR-driven outgassing in a large-format prismatic NMC811 cell through controlled heater-induced initiation and high-speed optical diagnostics. A series of four experiments were conducted under free-jet and obstructed-jet configurations, with synchronized voltage, surface temperature, and visual data acquisition. A dedicated image-processing pipeline based on OpenCV and TrackPy processed high-speed recordings at 35,200 frames per second to extract particle trajectories, velocities, and ejection angles from the free-jet test. The results indicate time-dependent particle discharge behavior characterized by high initial velocities, broad ejection angles, and subsequent directional shifts influenced by heater placement and local propagation of the exothermic reaction. Particle velocities were found to be comparable to those reported in the previous literature for small-format cells. Furthermore, ejection-angle analysis revealed a broad outgassing process with a total width exceeding 180°. The findings demonstrate the suitability of the proposed methodology for quantitative analysis of TR ejecta and provide new insights into the transient nature of particle-driven venting.

Source: Journal of Energy Storage

DOI: 10.1016/j.est.2026.125218