Layer-to-layer thermal runaway propagation of open-circuit cylindrical li-ion batteries: Effect of ambient pressure

Preventing thermal runaway propagation is crucial to ensure the safety of lithium-ion battery system, especially in low-pressure air-transport and the near-vacuum space environment. This work investigates the linear thermal-runaway propagation in LiNi_0.5Co_0.2Mn_0.3O₂ 18,650 cylindrical battery layers under ambient pressure from 0 atm to 1 atm. Results indicate that the 1-D layer-to-layer thermal runaway propagation rate decreases with decreasing SOC and ambient pressure. As the SOC decreases from 100 % to 30 %, the thermal runaway propagation rate decreases from 1.73 [layer/min] to 0.30 [layer/min] at 1 atm. For 30 % SOC cells, the thermal runaway propagation rate decreases by about 23 % as the ambient pressure decreases from 1 atm to 0.2 atm and eventually drops to zero at 0 atm. The X-ray computed tomography imaging reveals that low pressure can weaken both external flaming combustion and internal thermal runaway reactions during the venting stage. As the ambient pressure decreases, such dual effect increases the thermal runaway temperature from 200 to 310 °C, reduces the maximum surface temperature from 800 °C to 400 °C, and lowers the burning mass loss fraction from 32 % to 10 %. Finally, a simplified heat transfer model is proposed to explain the effects of SOC and ambient pressure on thermal runaway propagation. These findings provide a new way to mitigate the thermal runaway propagation and help to assess the safety of battery piles in storage and transport.