Study on Cooling Efficiency and Mechanism of Li-Ion Battery Thermal Runaway Inhibition by Additive Enhanced Water Mist Based on Boiling Heat Transfer Theory

Abstract

In recent years, fire and explosion accidents caused by thermal runaway (TR) of lithium-ion battery (LIB) have occurred frequently, which has become one of the main obstacles restricting its development. Therefore, it is urgent to develop fire extinguishing agents with high cooling efficiency to inhibit the growth of TR. The water mist is an effective choice, but it shows poor performance with the rise of cell temperature under TR. In this study, two additives, KCl and nonionic fluorocarbon surfactant FC-4430, were added into the water mist to improve the cooling efficiency. In addition, the inhibition effect exerted by the modified water mist during the whole process of lithium-ion battery TR was experimentally investigated. Furthermore, the influence of water mist with additives on the Leidenfrost effect in the high temperature range was deduced, and the reinforcement cooling mechanism was analyzed by heat transfer theory. The results show that KCl and FC-4430 can increase the initial cooling rate in the high temperature range by 48.6%-120%. The reinforcement mechanism is attributed to change the medium physical parameters by additives. On the one hand, the Leidenfrost point of the droplets on the cell surface is increased, which in turn extends the temperature range of the nucleate boiling stage, and on the other hand, the heat flux density and heat transfer of the water mist in the film boiling state are increased.

Keywords: Lithium-ion battery safety, Thermal runaway, Water mist, Additives, Suppression mechanism