Reproduction of the pressure load due to the thermal runaway in a flameproof enclosure by gas explosions

Lithium-ion batteries usage is rapidly growing due to their superior performance compared to other battery chemistries. However, they involve the risk of thermal runaway, which can cause catastrophic accidents. A large number of studies investigated the behaviour of cells undergoing thermal runaway. In hazardous areas, lithium-ion batteries may be used under specific conditions, for example in flameproof enclosures. However, there are few studies on this topic, limiting the information on how flameproof enclosures must be designed to contain a thermal runaway event and mitigate the risk. Notified bodies conducting type tests of flameproof enclosures usually do not have the capability to work with lithium-ion batteries in thermal runaway. However, gas explosions are regularly employed to test the enclosure's ability to withstand pressure. In order to replace the lengthy destructive tests with batteries in the future, it is envisioned to reproduce the pressure load due to the thermal runaway of a battery on the flameproof enclosure by a gas explosion. This work is the first step towards this goal. To this end, the temporal pressure development inside a flameproof enclosure during a thermal runaway of 18650 lithium-ion cell is reproduced by gas explosions. The cell was heated to thermal runaway in an air-filled flameproof enclosure and the resulting pressure was measured as a function of time. Initially, preliminary tests of different cell chemistries identified NMC811 and LCO as giving the highest load on the flameproof enclosure employed in this study. Due to its better reproducibility, NMC811 was selected as the load to be reproduced. Various combustibles in air were then ignited in the same flameproof enclosure without the cell. The highest pressure and the pressure rise time were varied by the type of combustible and its concentration in air. The burnable gases used were hydrogen, methane, propane, ethylene and acetylene in different mixtures with air. The results show that the pressure evolution due to the thermal runaway of the NMC811 cells can be reproduced by gas explosions.