Lithium-ion battery thermal runaway is a dynamic failure process involving cell heating, venting, gas evolution and, in many cases, ignition of flammable emissions. Understanding the time-resolved composition of these gases is critical for battery safety assessment, hazard modelling and the development of detection strategies. A recent study by researchers at the Health and Safety Executive Science and Research Centre, Real-time analysis of gases produced by induced failure of lithium-ion batteries, demonstrates how real-time gas analysis can provide detailed insight into the progression of lithium-ion cell failure across multiple chemistries, formats and abuse scenarios.
Investigating Gas Evolution During Thermal Runaway
The study examined gas emissions from cylindrical, pouch and prismatic lithium-ion cells with lithium nickel cobalt aluminium oxide (NCA), lithium nickel manganese cobalt oxide (NMC) and lithium iron phosphate (LFP) chemistries. Cylindrical 3–5 Ah cells were failed by external heating under nitrogen, while larger pouch and prismatic cells were failed by overcharge in air. This experimental design enabled the researchers to compare gas evolution as a function of cell chemistry, format, state of charge and failure mode, while capturing the timing of emissions during venting, thermal runaway onset and post-failure decay. Unlike static post-test gas collection, this real-time methodology provided a time-resolved view of how the gas hazard profile develops during the failure event.
Hiden HPR-20 Mass Spectrometry for Real-Time Failure Gas Analysis
A Hiden HPR-20 TMS mass spectrometer was used for real-time analysis of permanent gases and light hydrocarbons generated during cell failure. For cylindrical-cell tests, gases were sampled through a heated 190 °C line with particulate filtration, and the HPR-20 TMS operated using electron impact ionisation at a sampling rate of 2.6 Hz. Selected mass ions were monitored to quantify relative concentrations of H₂, CO, CO₂, CH₄, C₂H₄, C₂H₆, C₃H₆ and C₃H₈, with span gas measurements used to determine fragment ratios under the test conditions. In the larger-cell tests, the HPR-20 was combined with fourier transform infrared spectroscopy (FTIR) analysis, allowing permanent gases measured by mass spectrometry to be correlated with electrolyte carbonates and HF detected by infrared spectroscopy.
Chemistry-Dependent Gas Signatures
The real-time HPR-20 TMS data showed clear chemistry-dependent emission profiles. Nickel-based NCA and NMC cells generally produced H₂, CO and CO₂ as the dominant gases, with smaller quantities of light hydrocarbons, and often exhibited more aggressive failure behaviour at higher states of charge. LFP cells produced a contrasting signature, with H₂ typically dominating the permanent gas fraction when failure gases did not ignite. When ignition occurred, CO and CO₂ became more pronounced, illustrating the influence of combustion on measured gas composition. These results reinforce that gas emissions from battery failure cannot be generalised by format or capacity alone and must be evaluated for the specific chemistry and failure condition.
Linking Gas Composition to Failure Progression
The study showed that most permanent gas release occurred after thermal runaway had begun, although some cell-specific venting signatures were observed before full failure. For example, transient hydrocarbon release during safety vent opening was detected in selected cells, demonstrating the value of high-time-resolution mass spectrometry for identifying short-lived precursor events that would be difficult to capture by post-test sampling alone. The HPR-20 TMS measurements also helped distinguish between venting-stage emissions and thermal-runaway emissions, supporting more detailed interpretation of gas generation mechanisms, combustion effects and potential sensor targets for early warning applications.
Advancing Battery Safety Research with Time-Resolved Gas Analysis
By applying HPR-20 TMS mass spectrometry in real time, the researchers were able to characterise the timing, intensity and relative composition of gas emissions from different lithium-ion cell types under controlled abuse conditions. When combined with temperature measurement, video analysis and complementary FTIR detection of carbonate vapours and hydrogen fluoride, the HPR-20 TMS provided a robust analytical platform for studying thermal runaway chemistry. For battery safety scientists, these findings highlight the need for cell-specific gas analysis when assessing flammability, toxicity and detection strategies, particularly where chemistry, state of charge, abuse mode and atmosphere vary.
Conclusion
This study demonstrates the value of real-time HPR-20 TMS mass spectrometry for investigating lithium-ion battery failure gases as thermal runaway progresses. The instrument enabled rapid, multi-species monitoring of H₂, CO, CO₂ and light hydrocarbons, revealing chemistry-dependent and combustion-dependent gas signatures across cylindrical, pouch and prismatic cells. The work shows that time-resolved gas analysis is a powerful tool for understanding battery failure mechanisms and improving safety-focused testing methodologies.
Paper Reference:
Reeve, P. A. P., Buston, J. E. H., Howard, G. E., Goddard, S. L., Gill, J. and Mellor, J. W. (2026) ‘Real-time analysis of gases produced by induced failure of lithium-ion batteries.’ Journal of Energy Storage. Elsevier BV, 154, April, p. 121293. DOI: 10.1016/j.est.2026.121293.
