Self-heating ignition of open-circuit cylindrical Li-ion battery pile: Towards fire-safe storage and transport

•Tests show self-ignition of cylindrical LIB piles at the ambient temperature of 135–192 °C.•Critical self-ignition ambient temperature decreases with increasing battery SOC and pile size.•Self- ignition of Li-ion battery follows the classical theory and similar to hydrocarbon fuels.•F-K analysis predicts the possibility of self-ignition of large battery pile at ambient temperature.•Adding gap between battery layers can reduce the self-ignited fire risk in transport and storage. The battery fire accidents frequently occur during the storage and transportation of massive Lithium-ion batteries, posing a severe threat to the energy-storage system and public safety. This work experimentally investigated the self-heating ignition of open-circuit 18650 cylindrical battery piles with the state of charge (SOC) from 30% to 100% and the cell number up to 19. As the ambient temperature increases, the self-heating ignition occurs and leads to a violent fire. The characteristic temperatures for both electrolyte leaking and thermal runaway decrease with SOC. The critical ambient temperature for self-heating ignition ranges from 135 °C to 192 °C, and it decreases with the increasing battery SOC, cell number, and pile size, which satisfies the self-ignition theory. The applied Frank-Kamenetskii analysis predicts the self-ignition ambient temperature could be lower to 30 °C for large battery piles with multiple tightly packed layers, such as those in the shipping container and warehouse. Nevertheless, creating gaps and providing effective cooling between each battery layer could effectively lower the fire risk by increasing the self-ignition ambient temperature above 125 °C. This work theoretically reveals the self-ignition characteristics of open-circuit battery piles, which could provide scientific guidelines to improve battery safety and reduce fire hazards during storage and transportation. [Display omitted]