Abstract: The efficacy of fine water mist as a cooling medium has garnered acclaim for its superior performance in mitigating thermal runaway phenomena within lithium-ion batteries. This investigation comprehensively evaluates the role of heat dissipation from safety valve-released gases and assesses the suppressive effects of fine water mist on the progression of thermal runaway at various stages. The study meticulously analyzes the thermal dynamics throughout the thermal runaway event, elucidating the kinetic principles that underpin the interaction between the battery flame and the fine water mist. The salient findings from this research are as follows: A critical threshold of accumulated heat density is identified, beyond which the fine water mist's cooling effect fails to inhibit thermal runaway, although it substantially diminishes the cooling duration post-thermal runaway; The initiation of thermal runaway is accompanied by a dynamic interaction with the fine water mist, which is observed to alter the flame's morphology and to increase the interfacial pressure significantly. This research introduces a novel cooling efficacy factor that quantifies the equilibrium state between the fine water mist and the thermal runaway flame, providing a nuanced assessment of the cooling strategy's effectiveness.

Key words: lithium-ion batteries, fine water mist, thermal runaway, accumulated heat density, cooling