Flammability of Lithium-Ion Battery Vent Gas: The Combined Effect of Cell Chemistry, State of Charge, and Failure Phase

This study presents a comprehensive risk assessment of battery vent gas (BVG) from lithium-ion cells, focusing on its dynamic composition and laminar burning velocity (S u ). It highlights lithium titanate (LTO) cells, which use Li 4 Ti 5 O 12 anode, and compares them with NMC, NCA, and LFP chemistries. LTO cells improved safety by mitigating lithium plating and dendrite growth, key causes of internal short circuits and thermal runaway (TR). BVG composition evolves significantly during TR and depends on cell chemistry and state of charge (SoC), affecting combustion behaviour. BVG composition and S u were quantified during different stages of thermal abuse for cells with various chemistries and SoC (50% and 100%). A lab-scale setup with FT-IR and Micro-GC identified gases such as H 2 , CO, CO 2 , CH 4 , HF, and organic carbonates. Additional analyses (FT-IR) identified unburned species, while CHEMKIN-Premix calculated S u and sensitivity factors. Results show that LTO and LFP cells are safer under thermal abuse. At 100% SoC, NMC produced the most hazardous BVG, with higher hydrogen and the highest S u . At 50% SoC, TR was suppressed for LTO and LFP cells. These findings provide key insights into combustion dynamics and support improved mitigation of fire and explosion hazards in lithium-ion batteries.