| Lithium ion batteries have the advantages of high charging efficiency,high energy density,long cycle life,green environmental protection,etc.,and become the most widely used energy storage in electrochemical energy storage.Among them,the lithium iron phosphate battery has become the most competitive battery technology in the electrochemical energy storage power station in China at present due to its excellent safety,excellent cycle life and low cost.However,the chemical characteristics inherent in lithium-ion batteries have led to frequent fire safety accidents,endangering the safety of people’s lives and property,and hindering their safe and efficient development.Therefore,it is particularly necessary to carry out research on the suppression methods of thermal runaway of lithium iron phosphate battery for energy storage.Based on the thermal runaway characteristics of lithium iron phosphate battery,experiments on thermal runaway and propagation characteristics of single battery and battery module were carried out,and the inhibition effects of different nitrogen injection parameters on thermal runaway of single battery and battery module were analyzed,which provided a theoretical basis for the engineering application of liquid nitrogen in the field of energy storage.The main work is as follows:(1)Research on thermal runaway characteristics of different SOC single cell batteries.With the increase of SOC,the scale of thermal runaway fires in batteries increases,resulting in more mass loss and higher CO content.The triggering temperature and time of thermal runaway decrease,and the maximum temperature of thermal runaway increases.The rapid accumulation of thermal runaway heat in batteries mainly occurs during the self heating explosion stage.The larger the SOC,the more heat accumulates during the thermal runaway process.At 100% SOC,the maximum heat accumulated is 663.79 k J,and the fastest heat accumulation speed is 20.39 k W.(2)Research on thermal runaway and propagation characteristics of battery modules at different heating positions.The one-sided heating condition only triggered the thermal runaway of two batteries and the opening of one battery safety valve,while the intermediate heating method caused the thermal runaway of six batteries,and all the safety valves of the first row of batteries were opened.The propagation path of thermal runaway has been determined: the thermal runaway propagation path of the unilateral heating battery module is 1#→2#→3#,and the thermal runaway propagation direction of the intermediate heating battery module is 3#→2#→1#.The thermal runaway generated by the 1# battery is transferred back to the 2# battery,and the propagation path on the other side of the heating plate is 4#→5#→6#.The thermal runaway generated by the 6# battery continues to transfer heat to the 7# battery,while the other part is transferred back to the 5# battery.Under unilateral heating conditions,the thermal runaway module has no significant impact on the battery cluster.Under intermediate heating conditions,the thermal runaway module has a significant impact on the upper and lower modules in the battery cluster,and there is a risk of chain reaction and thermal runaway in the upper and lower modules.(3)Research on the inhibitory effect of liquid nitrogen on thermal runaway of single cell batteries under different nitrogen injection parameters.Injecting a small amount of liquid nitrogen before the safety valve of the battery is opened can prevent the occurrence of thermal runaway.Injecting at the highest temperature of thermal runaway can extinguish the battery fire within 8 seconds.The intermittent nitrogen injection method is superior to continuous nitrogen injection;If the nitrogen injection amount is too much,the cooling efficiency will decrease.The best effect is when the nitrogen injection amount is 8kg,with an actual temperature drop of 98.5 ℃ and a cooling efficiency of 0.040;When the nitrogen injection pipe diameter is 20 mm,the suppression effect is better,and there is an optimal pipe diameter,which can achieve the optimal cooling efficiency and actual cooling.(4)The study on the suppression effect of liquid nitrogen on thermal runaway of battery modules in energy storage prefabricated cabins under different nitrogen injection parameters shows that liquid nitrogen can extinguish battery module fires within 10 seconds.The larger the nitrogen injection amount,the greater the actual cooling,but the cooling efficiency decreases.When the nitrogen injection amount is13 kg,the highest efficiency is 0.061.Considering the economy,a nitrogen injection amount of 13 kg is more suitable for suppressing the thermal runaway of the battery module in this experiment;When the nitrogen injection position is above the battery module,only one battery experiences thermal runaway.When the nitrogen injection position is behind and to the left,two batteries experience thermal runaway.The nitrogen injection position above is more helpful in suppressing the thermal runaway of the battery module;The smaller the diameter of the nitrogen injection pipe,the faster the outlet flow rate,and the stronger the impact on the battery.However,the contact area with the battery surface decreases.The larger the diameter of the nitrogen injection pipe,the slower the outlet flow rate,and the inability to cool the battery in a timely manner,resulting in lower cooling capacity and efficiency.When the diameter of the nitrogen injection pipe is 20 mm,the inhibitory effect is optimal.This thesis has 70 images,24 tables,and 70 references. |
