Detailed characterization of solid particles emitted during the thermal runaway of large-scale Lithium-ion cells

Lithium-ion battery (LIB) technology provides high energy density, long cycle life and low self-discharge rates, thus it has become a popular choice for many applications. Despite this success, the safety of LIBs remains a major concern due to the potential risk of thermal runaway (TR), leading to the ejection of battery materials. In this work, the particle emissions, vented gas volume and energy released during the TR of a large prismatic lithium-ion NMC rich cell are characterized. Among the total energy released during thermal runaway (1.2 times the electrical energy stored in the cell), 78 % is contained in the ejecta, which represent only 38 % of the total mass of the initial cell. After thermal runaway, the particles were collected and analyzed. Sieving revealed that the majority of the particles were smaller than 75 μm. The elemental quantifications conducted on each subsample revealed a decrease in the proportion of cathodic transition metals and an increase in the proportion of carbon, primarily graphite, as a function of particle size. Furthermore, stoichiometries of nickel, cobalt, and manganese remained constant across all the samples, indicating that TR did not alter the NMC arrangement. Particle density decreased with size, and the specific surface areas also highlighted the coarse and porous nature of the structures. The granulometry measurements enabled quantifying the degree of particle agglomeration relative to particle size. Finally, the analysis revealed that the agglomerates were mainly composed of three families of fine particles (NMC oxides and graphite carbon) which adhered to larger particles during TR. • Thermal runaway of a 144 Ah prismatic NMC cell in a closed and insulated vessel • Identification of particles and gases contribution in total thermal runaway energy • Proportion evolution of transition metals and graphite with the particle size