Comprehensive gas analysis of a 21700 Li(Ni0.8Co0.1Mn0.1O2) cell using mass spectrometry

The failure of lithium-ion batteries (LIBs) can be partly defined by the release of toxic and flammable gases. The composition and volume of these gases varies depending on cell type, failure mechanism, state of charge (SoC) and environmental oxygen (O2) levels. Understanding this relationship and the species produced is essential for battery pack manufacturers relying on real-time monitoring to assess the state-of-health (SoH) of a LIB. It also has ramifications for emergency responders attending thermal runaway (TR) events. In this work, NMC-811 21700 cells were overheated, and the resulting gas analysed in real-time using mass spectrometry (MS). Repeat tests were conducted to account for variability. Work has been carried out to both quantify the volume of gas produced and investigate how gas composition changes during different stages of cell failure. Tests were conducted at 5–100% SoC. Results showed that during safety venting (SV), the major constituent gas is methane (CH4), which was positively correlated with SoC. In contrast, during TR the gas mixture contains hydrogen (H2), carbon dioxide (CO2) and carbon monoxide (CO). Further analysis to quantify gas volumes show a 3 to 5-fold increase, in both air and nitrogen (N2) atmospheres, when SoC is increased from 25% to 100%.