Solid-Ejecta Morphology and Elemental Composition During Thermal Runaway of 58 Ah NCM811 Lithium-Ion Cells: Representative Near-Field Thermal-Flow Behavior

Thermal runaway (TR) of lithium-ion batteries generates both gaseous and solid ejecta, yet the material characteristics of the expelled solids and their surrounding thermal-flow environment are often examined separately. In this study, solid ejecta recovered from three repeated thermal-runaway tests of 58 Ah Li(Ni0.8Co0.1Mn0.1)O2 (NCM811) cells under nitrogen were characterized using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). A separate two-dimensional reacting-jet model was established to provide representative near-field thermal-flow context under a high-intensity ejection condition in ambient air. SEM observations at 500×–10,000× revealed irregular fragments, lamellar structures, agglomerates, and fine-particle deposits, indicating pronounced morphological heterogeneity of the recovered solids. In the local selected EDS region, Ni, Mn, and Co collectively accounted for 54.61 wt.% of the normalized elemental signal, together with substantial C, O, and F. The numerical model employed a reduced CO2-CO-H2-O2 mixture, a 12.5 mm vent inlet width, an inlet velocity of 90 m/s, and an inlet temperature of 941.2 °C. The maximum resolved velocity reached approximately 104 m/s near the vent, whereas the maximum simulated temperature was approximately 1806 °C, which occurred farther downstream. These results provide complementary insight into the post-failure material characteristics of solid ejecta and the representative near-field thermal-flow behavior associated with severe lithium-ion battery thermal runaway. The numerical results are intended as representative spatial context rather than a direct reconstruction of the nitrogen-atmosphere experiments.