Time-resolved characterization of toxic and flammable gases during venting of Li-ion cylindrical cells with current interrupt devices

Large-scale battery failures can lead to explosion and toxicity hazards. Mitigation of battery hazards requires accurate data of battery flammable and toxic gas composition and early indicators of failure. In this study, NMC and LFP cathode cylindrical format lithium-ion batteries were failed using external heating to characterize the time evolution of evolved gases as the current interrupt devices (CID) activated. Measurements included the cell surface temperature, voltage, and gas composition using a near-source gas sampling system with a Fourier-transform infrared spectrometer (FTIR). Three early indicators of cell failure venting, which releases toxic and flammable gases, were identified. First, dimethyl carbonate (DMC), ethylene carbonate (EC), and hydrogen fluoride (HF) were the first detected species once the cell vents. Second, the voltage drop due to CID activation correlates with cell venting. The time gap between CID activation and the burst disk rupture that allows gases to be released by the cell is 27 ± 9 s and 16 ± 6 s for LFP and NMC cells, respectively. Third, the cell surface temperature at which the CID activates is 208 ± 29 °C for the LFP cells and 212 ± 15 °C for the NMC cells. Using CO as an internal standard for quantitative analysis, the CO${}_2$/CO ratio verified that the near-source gas sampling system gives similar results compared to literature data. This serves as a method for quantitatively measuring the HF concentration using the HF/CO ratio. The DMC/CO ratio revealed that DMC is abundant and contributes to the overall gas flammability in addition to the more typically-reported dry vent gases. This study recommends that flammability models for battery systems include the vented electrolyte components to more accurately predict the explosion hazards.