Evaluation of the laminar burning velocity of various battery vent gases emitted during the thermal runaway of Li-ion cells

The rapid expansion of lithium-ion battery (LIB) technology across energy storage and transportation sectors raises significant safety concerns due to potential fire and explosion risks. Thermal runaway (TR) events in LIBs can release flammable gases, thereby posing heightened fire hazards. However, data on the flammability characteristics of gases emitted during thermal failure remain limited. This study addresses this gap by evaluating the laminar burning velocity (Su), a key safety parameter, using both experimental and modeling approaches to understand the influence of cell chemistry on LIB behavior. Three commercial cylindrical cells—Lithium Nickel Cobalt Aluminium Oxide (NCA), Lithium Iron Phosphate (LFP), and Lithium Nickel Manganese Cobalt Oxide (NMC)—were tested at a 100 % state of charge (SoC). Cells were subjected to controlled heating at a rate of 5 °C/min in a laboratory setup equipped with Fourier Transform-Infrared Spectroscopy (FT-IR) and a micro-GC for real-time gas analysis. Major battery vent gas (BVG) components detected during TR event included H2, CH4, CO, CO2, HF, and vapours of electrolyte solvents like dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethylene carbonate (EC). The Su values were calculated using a one-dimensional laminar premixed flame model within the CHEMKIN software, with continuous gas monitoring throughout the entire thermal failure event. These calculations considered different BVG compositions during specific phases—venting, TR, and overall event phases—each critical depending on cell chemistry. For NCA cells, the TR phase exhibited the most critical BVG composition, while for LFP and NMC cells, the venting phase proved more critical, largely due to H2 emissions. Furthermore, the effect of TR-induced temperature on Su was evaluated through simulations conducted at 25 °C, 150 °C, 300 °C, and 500 °C at 1 atm.