Abstract: In order to explore the thermal characteristics of lithium-ion batteries under different environmental pressures, thermal runaway experiments of 18650 cylindrical lithium- ion batteries with 100% SOC (state of charge) under different environmental pressures (30 kPa, 50 kPa, 70 kPa, 90 kPa) were carried out with dynamic pressure and temperature chamber and ISO-9705 flue gas analyzer. The results show that the thermal runaway caused by external heat source can be divided into three stages in either normal pressure or low pressure environment. With the decrease of the environmental pressure, the peak temperature, heat release rate and total heat release rate of the battery surface decrease, and the detonation response time point is prolonged; at 30 kPa, the explosion response time point is 515 s, which is 348 s longer than that under 90 kPa condition. The peak temperature of the thermal surface of the battery is 703 ℃ at 90 kPa, which is 1.299 times of that under 30 kPa.With the decrease of environmental pressure, the release of CO gas increases gradually, while that of CO2 and CxHy decreases gradually. It can be seen that the lithium-ion battery in normal pressure environment has higher thermal hazard. In low- pressure environment, it will have greater risk of toxic hazard.

Key words: lithium- ion battery, thermal runaway, state of charge, heat release rate