| Owing to the multiple advantages,lithium ion batteries(LIBs)have been widely utilized in the electric vehicle and energy storage industries since commercialization.However,extreme thermal hazard that known as the thermal runaway(TR)can be triggered under abusive conditions.The heat released during TR will be transferred to adjacent LIBs,leading to the TR propagation.Consequently,large scale LIB fire or even explosion hazard can be triggered.The safety problem has become a serious concern and hindered the further development of the emerging industries,for instance the electric vehicle industry.However,the prevention of the LIB TR hazard remains a technical barrier.Effective countermeasures are urgently needed and relevant researches have to be conducted to guarantee the LIB safety during usage.The TR is caused by the self-heating under abusive conditions,and cooling suppression can be a pertinent method to mitigate the hazard.As a kind of clean and efficient cooling strategy,water mist(WM)has been widely utilized to suppress the fire hazard,especially the electrical fire.However,relevant study on the cooling control effect of WM on the LIB TR is still lack,and systematic and comprehensive research is necessary to cover this research gap.A series of experiments have been conducted with the self-made experimental platform.The WM cooling control mechanisms have been revealed,and the critical control temperature(Tc)has been proposed,which can be seen as the threshold for hazard control.The method of developing the WM cooling control system for the TR suppression has also been presented.Main researches are as follows:Firstly,a small scale experimental platform has been built and the WM cooling suppression effect on the 18650 type LIB has been studied.TR characteristics under various state of charges(SOCs)have been analyzed.The Tc of the WM has been deduced according to the relationship between the battery self-heating and the WM cooling,which has been verified with the experiments.The Tc presents decreasing process with the increase of SOC,and a conservative Tc that can be utilized to guide the TR control in real cases has been proposed.Meanwhile,the LIBs that experienced WM cooling suppression remain the possibility of triggering TR,but with mitigated hazard phenomenon.The effectiveness of WM cooling on the TR control has been primarily verified through the experiment.Secondly,considering the diversity of TR under various conditions,an experimental platform for large format LIBs has been built,and WM cooling suppression tests on large format LIBs have been conducted to further verify the effectiveness of WM cooling.The development process of TR has been divided into different stages according to the variations of temperature,voltage,and gases,and a key inflection has been identified.Accordingly,comprehensive analysis on the hazard control has been conducted considering the fire suppression,battery cooling,and the WM cooling efficiency.Results show that the TR can be effectively mitigated at various hazard stages.The battery flame can be suppressed within few seconds,and significant cooling capacity can be obtained even under the TR condition.Compared to the thermal abuse tests,similar WM cooling characteristics have been obtained under the overcharge tests.Thirdly,the WM cooling suppression effect on the TR propagation has been further studied based on the single battery tests.The behaviors of TR propagation have been comprehensively revealed,and the effectiveness of the WM cooling under various hazard stages has been analyzed.The influence of WM duration has also been considered.Results show that the TR propagation can be efficiently prevented with the WM cooling,and the water consumption is calculated to be 2.0 × 10-4 kgWh-1 for the studied 18650-type module.The evaporation of WM droplets has been identified as the dominating mechanism during cooling,and the maximum cooling rate of the LIB exceeds 100℃s-1.Considering the heat transfer,the Tc has been extended into the temperature range of(Tc1,Tc2)to guide the hazard control of the TR propagation.Fourthly,the TR propagation behaviors under various triggering conditions have been studied from the perspective of cooling control,and the method of developing the TR cooling control system has been further discussed.The variations of dynamic and thermal parameters during the TR propagation have been comprehensively analyzed under various conditions,and the effectiveness on characterizing the essence of TR hazard has been further discussed.The complex relationships among various parameters have been exhaustively combed,and critical parameters are identified,such as the maximum heating rate and the total heat accumulation.Accordingly,the minimum cooling rate and total heat absorption of the cooling system can be roughly determined.In addition,a more applicable and practical method of developing the TR cooling control system has been proposed.This study has confirmed the effectiveness and characteristic of the WM cooling on the TR suppression from the perspective of cell level and module level,respectively,which is beneficial for the practical engineering. |
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