Abstract: In order to study characteristics of lithium ion batteries during thermal runaway process, inert gas was added on the basis of water mist to carry out fire suppression test of lithium ion batteries. Lithium iron phosphate batteries with charge states of 0%, 50% and 100% were selected to conduct thermal runaway research in air, N₂ and CO₂ gas environments respectively. On the basis of the research on thermal runaway of lithium ion battery, the fire extinguishing test of lithium ion battery was carried out by using water spray device, and the thermal runaway process, temperature change, fire extinguishing time and other parameters were compared and analyzed. The results show that the thermal runaway of lithium ion battery goes through stages of burst valve, initial fire, stable combustion, flame attenuation, flame extinction and flame reignition, that both N₂ and CO₂ can reduce the combustion temperature and explosion intensity of lithium ion battery, and that CO₂ and pure water mist can inhibit the combustion of lithium ion battery better than N₂ and pure water mist, which proves the synergistic inhibition effect of inert gas and water mist on lithium ion battery fire.

Key words: lithium ion battery, fire, inert gas, water mist, suppression of explosion