Study Of Water Spray On The Thermal Runaway Suppression And Performance Impact Of Ternary Power Lithium-ion Battery

As a new type of energy storage medium,lithium-ion batteries(LIBs)are favored because of their high energy density,excellent performance and other advantages.They are widely used in emerging fields such as new energy vehicles and become a key link in the new energy industry chain.However,LIBs are easy to cause fire and release toxic gases under abuse conditions,which pose a serious threat to human life and property safety.However,LIBs storage warehouse,electric bicycle charging shed,new energy vehicle charging station and other places still lack effective fire fighting measures.In order to ensure the healthy development of the industry,it is urgent to carry out relevant research on fire fighting of LIBs.Main researches are as follows:Firstly,the suppression efficiency of common fire extinguishing agents for thermal runaway propagation(TRP)of ternary power LIBs is compared to selected the better fire suppression agent.The results show that the cooling efficiency of fire extinguishing agent is very important to suppress TRP.Compatison from the cooling efficiency and TRP inhibition efficiency,the order is water spay,C6F12O and heptafluoropropane.Thus,water spray is identified as the proper extinguishing agent for ternary power LIBs fires under low voltage system.Secondly,the suppression efficiency of water spray with different parameters on LIBs fire is studied,and the cooling efficiency is quantified.The selection model of critical water volume to suppress LIBs fire is established,and the effect of water spray on gas toxicity of LIBs fire is evaluated.Water spray has excellent fire suppression and cooling capacity,but the cooling efficiency is lower(close to 15%).When the volume is constant,the cooling efficiency decreases with the increase of spray intensity.Based on the cooling mechanism dominated by the latent heat of evaporation,this paper establishes a selection model of critical water volume to suppress LIBs fire.The critical volume of water spray in cooling and suppressing TRP is 2.34 kg/kWh and 1.45 kg/kWh,respectively.During the water spray application,the gas toxicity will be increased in a short time,making it reach the dangerous critical value earlier,but the maximum value is reduced.With good ventilation measures,it can not exceed the dangerous critical value.Thirdly,the enhanced cooling strategy of water spray to suppress LIBs fire is proposed and optimized,and the cooling mechanism of intermittent spray on LIBs fire is revealed.The results show that the intermittent spray enhances the convective and evaporation heat transfer of the liquid film,which improves the cooling efficiency.Meanwhile,the cooling efficiency increases with decreasing intermittent period,and initially increases and then decreases with decreasing duty cycle.The cooling efficiency with an optimal duty cycle in this paper is up to 62.48%.The suppression capability of TRP is closely related to the total heat absorption and cooling power.An inhibition factor(fc)during TRP is proposed.When fc is positive,the cooling effect dominates the process of TRP inhibition.In addition,the suppression strategy is optimized.Firstly,a spray method with better suppression ability is used to extinguish the flame and eliminate the threat of TRP in the initial stage.After the flame is extinguished,the spray method with high cooling efficiency is used to accelerate the cooling process.Finally,the aging mechanism of immersion cell was revealed,and the thermal runaway critical condition model was established based on the thermal spontaneous theory.The self-accelerating decomposition temperature(SADT)of the immersion cell was calculated,and the applicable scope of water spray was defined.The corrosion degree of immersion cell increases with increasing voltage,solution conductivity and immersion time.When the conductivity exceeds 39.3 ms/cm,the capacity of the immersion cell decreases and aging speed increases.The aging mechanism of immersion cell is analyzed by electrochemical impedance spectroscopy,and it is clarified that the loss of active material caused by the corrosion of safety valve which destroys the material structure of the cell is the main aging mode.The thermal stability and SADT of the immersion cell also decreases.Meanwhile,the thermal stability and SADT of immersion cell decrease with increasing immersion time.When the safety valve is corroded,the SADT of immersion cell is lower and the risk of spontaneous ignition is higher with the situation of poor heat dissipation.While improve ventilation conditions can significantly increase the SADT of immersion cell.In fresh water,with increase of voltage,the impact of electrical energy consumption is dominant,and the thermal stability and SADT increase.Therefore,water spray has limited impact on the system when extinguishing the battery fire within the system voltage of 200 V.