| Due to high energy density,low environmental effects and excellent cycling capability,lithium-ion batteries are gradually developing into an important cornerstone of the new energy industry,which are widely used in emerging fields such as electric vehicles.However,due to the active material nature of lithium-ion batteries,abuse based thermal runaway trends to occur,and then easily develops into large-scale fire and explosion accidents,which seriously threatens the safety of life and property of the users,and is a technical bottleneck that urgently needs to be broken.The existing safety protection measures and technologies cannot effectively block the thermal runaway and suppress the lithium ion battery fire.Therefore,this paper focuses on the new clean fire extinguishment agent dodecafluoro-2-methylpentan-3-one(C6F12O),studies its fire extinguishing efficiency and mechanism for NCM ternary power lithium-ion batteries,and proposes a dose selection empirical method and new extinguishment strategy,which is of great significance for the development and improvement of relevant regulations and new technologies.Firstly,the fire suppression efficiency of various fire suppression agent for ternary power lithium-ion batteries is investigated,and the flame suppression effect and cooling effect of various fire suppression agent are explored to reveal the better fire suppression agent for ternary power lithium-ion battery fires.The results show that the existing extinguishing agent cannot fundamentally cut off the thermal runaway chain reaction inside the battery,but the fire and thermal hazard of the system can be reduced by chemical inhibition and physical cooling.The experimental results show that C6F12O,heptafluoropropane,water spray and ABC dry powder can efficiently extinguish the battery fire without reignition,CO2 can extinguish battery fire but reignition occurs.Comparing the cooling effects of abovementioned agents,the order is water spay,C6F12O,heptafluoropropane,ABC dry powder and CO2.Considering suppression efficiency,cooling efficiency and application feasibility,C6F12O was identified as the most appropriate extinguishing agent for ternary power lithium-ion battery fires.Secondly,the fire suppression efficiency of various doses of C6F12O on ternary power lithium-ion battery is further investigated and revealed,and the selection empirical model and method of the optimal dose for C6F12O are proposed.The results show that C6F12O with all tested doses can efficiently extinguish the open flame within 3 s.When the dose is less,the deep smoldering still occurs inside the battery.As the dose of C6F12O increases,the peak temperature of the long surface and the bottom surface of the cell increases slowly at fist and then decreases rapidly,and there is a critical inhibition dose in the suppression system.In this work,the proper dose selection model of C6F12O in extinguishing battery fire is established by coupling the critical inhibition dose of several characteristic surface,and with tight constrained and suppressed when thermal runaway,the optimal dose of C6F12O in suppressing 100%state of charge(SOC)ternary power battery fire is 9.42g/Wh.Thirdly,the reaction potential energy surface between C6F12O and combustion radicals is established,and the pressure and temperature-dependent rate coefficients are calculated to reveal the suppression mechanism of C6F12O.The results show that the reaction between C6F12O and combustion radicals mainly comes from the carbonyl,and the addition and subsequent bond-breaking reactions between C6F12O and combustion radicals are the main reaction channels.The abstraction and substitution contribute less to the reaction mechanism.The suppression effect of C6F12O mainly comes from the reaction between the C6F12O and subsequent products with H and OH radicals.The effect of C6F12O on the system toxicity is mainly related to the reaction between C6F12O and H radicals.In addition,the cooling enhancement strategy in C6F12O suppression for ternary power lithium-ion battery fire is proposed,and the challenge of continuous high temperature in the cell after suppression is optimized.The application of water mist effectively cools the batteries extinguished with C6F12O,and for the battery with 100%SOC,with tight pretightening and suppressed when thermal runaway occurred,the average cooling efficiency in test with C6F12O&water mist increases by 147.9%,141.7%and 204.9%compared to C6F12O only,water mist only and without suppression.The cooling efficiency increases with the decreasing of the delay time between the application of C6F12O and water mist.As the working pressure increases,the spray momentum of droplets increases,the boiling heat transfer is enhanced,thus the water mist exerts better cooling effect for the extinguished battery.In addition,the additives can effectively enhance the cooling effect of water mist,water mist with salt additives shows better cooling effect compared to surfactants.Finally,the extinguishment efficiency of C6F12O for high energy density(HED)ternary battery and module are investigated,and the effect of system flow rate and different thermal runaway trigger position on the suppression effect are analyzed.The results show that C6F12O can efficiently extinguish the HED battery and its module fire,and the optional dose selection method and empirical model are still applicable in HED battery fire suppression.As the flow rate increases,the extinguishment time decreases and the battery peak temperature reduces,but the agent loss increases and the spray time shortens,then the cooling efficiency for the long-term process is decreased.In addition,when the C6F12O spray can completely cover the thermal runaway area,its extinguishing and cooling effect for the battery is the best.For the thermal runaway and suppression of battery module,the application of C6F12O effectively increases the thermal runaway trigger temperature,reduces the thermal runaway peak temperature,and decreases the heat production of battery module.The application of water mist system enhances the cooling of extinguished batteries,and the combination of C6F12O and water mist extend the thermal runaway propagation time of fully charged battery module to 1.4 times compared to those without suppression,and the total thermal runaway heat production was reduced by 1703.9kJ. |
PDF Full Text Request