Fire Tests on E-vehicle Battery Cells and Packs

Area of Science:

• Materials Science
• Electrochemistry
• Fire Safety Engineering

Background:

• Electric vehicles (EVs) utilize lithium-ion (Li-ion) batteries, necessitating research into their behavior under abuse conditions like fire.
• Understanding Li-ion battery thermal runaway and toxic gas emissions is critical for developing effective emergency response protocols.

Purpose of the Study:

• To assess the impact of crash scenarios and abuse conditions on Li-ion battery systems in EVs.
• To inform the development of safe practices and response priorities for accidents involving EVs.

Main Methods:

• External fire tests were conducted on commercial Li-ion battery cells and packs (Lithium iron phosphate - LFP, and lithium nickel manganese cobalt oxide - NMC).
• Oxygen consumption calorimetry measured heat release rate (HRR), and Fourier transform infrared spectroscopy (FTIR) quantified toxic gas concentrations.
• Pouch-type cells with varying capacities (7 Ah LFP, 14 Ah NMC) were tested.

Main Results:

• State of charge (SOC) significantly influences HRR and hydrogen fluoride (HF) gas generation.
• Larger cell assemblies increase HF formation per cell.
• NMC cells exhibit higher overall reactivity, while LFP cells produce more HF per cell.
• Total energy released during combustion is independent of SOC, driven by stored chemical energy.

Conclusions:

• Extrapolating single-cell test data to predict higher-order system behavior (e.g., HF emissions, energy release rates) is challenging.
• Inter-cell mass and shielding effects in multicell assemblies critically impact thermal event propagation.