Thermal Runaway Experiments on High-Capacity Lithium-Ion Cells

Li-ion cells (LIC) are regarded as a very promising technology for energy storage systems due to their high energy density and good cycling stability. However, they still have several shortcomings, especially in terms of safety. Under off-nominal conditions, LIC can experience thermal runaway that can lead to fire and explosion hazards. To understand the triggering conditions of thermal runaway, as well as its consequences, thermal abuse tests on fully charged high-capacity LIC were carried out. Three types of LIC, namely lithium-nickel-manganese-cobalt, super lithium-iron-phosphate, and lithium-nickel-cobalt-aluminum, with nominal capacities of 28, 39, and 42.2 Ah respectively, were selected. Measurements included cell mass loss, gas temperature, vent bursting and thermal runaway delays. The test results showed that the effects of runaway are all the more important as the capacity (energy stored) of the cell is high. With increasing capacity, thermal runaway occurs earlier, and different failure modes can be observed: a slow combustion with diffusion flame, aggressive jet flame containing molten metal particles, up to a fireball ejecting all the contents of the cell.