Study On Fire Suppression Mechanism Of Lithium Ion Batteries By Water Mist Containing Additives

Lithium ion batteries have been widely used in many fields.However,thermal runaway in the storage and use of lithium batteries poses a great threat to users,especially after repeated charging and discharging,the battery continues to age,and the risk of thermal runaway of lithium batteries increases.In this paper,the self-designed experimental platform was used to study the inhibitory effect of water mist pressure,additive concentration and type on thermal runaway of different aged batteries.The main conclusions are as follows:The thermal failure process of 18650 lithium battery generally includes four stages:heating,initial explosion,ignition explosion and cooling.With the increase of the number of battery cycles,the quality of lithium battery becomes worse and worse,and the trigger time of ignition and explosion gradually decreases.After the ignition and explosion,the battery surface temperature and flame temperature decrease.In addition,the number of cycles up to 20 lithium battery combustion is the most intense,the largest flame area.An experimental platform built with existing equipment was used to carry out an experimental study on the detonation inhibition effect of water mist under different pressures on the 0-cycle and 20-cycle 18650 lithium battery.It is found that for new lithium batteries,the comprehensive inhibition effect of 0.2-0.25MPa pressure water mist is better than that of 0.1-0.15MPa,0.3MPa water mist.For 20 cycles lithium battery,the comprehensive inhibition effect of 0.25-0.3MPa fine water mist is better than that of 0.1-0.2MPa fine water mist,and the suppression effect of 0.25MPa fine water mist droplets with SMD particle size of 71.3μm is the best for 18650 lithium battery.Different additives have different inhibitory effects on the thermal failure behavior of lithium batteries with different cycle times.Sodium dodecylbenzene sulfonate（SDBS）can improve the heat absorption capacity of water mist,and1.5%SDBS can obviously enhance the inhibition effect of water mist on the flame of0-cycle and 20-cycle lithium battery.The ions dissociated by sodium chloride will bind to free radicals in the combustion reaction chain,thus inhibiting the chain reaction.Adding 1.0%sodium chloride can obviously enhance the flame suppression effect of water mist on 0-cycle and 20-cycle lithium batteries.Protein generates inert gas through endothermic thermal decomposition,and generates carbonized layer through high-temperature decomposition,oxidation and dehydration to isolate air,together with fine water mist,to inhibit the combustion and explosion of lithium battery.1.5%protein content can obviously enhance the suppression effect of fine water mist on 0-cycle and 20-cycle lithium-ion batteries.Different additives have different inhibitory effects on the ignition and explosion of the same lithium battery.For the lithium battery with 20 cycles,the battery has a certain degree of aging,and the most severe ignition and explosion occurred.The chemical action of 1.0%sodium chloride water mist and cooling endothermic action were synergistic and the chemical action of sodium chloride played a dominant role,effectively inhibiting the battery flame combustion and internal chemical exothermic reaction.Lithium battery for 40 cycles,the increase of aging degree,combustion occurs flame area is relatively small,relatively low flame temperature,then water mist cooling heat absorption effect of the main inhibition,the addition of 1.5%SDBS makes the water mist droplets size and infiltrating effect to strengthen at the same time,makes the water mist can give full play to its cooling endothermic effect best inhibition effect.For the new battery with 0 cycles,the three additives all showed good synergistic effect,and 1.5%protein water mist had obvious inhibitory effect on the flame of the new battery.Fluent software was used to simulate the thermal failure experiments of different inhibitors to suppress the thermal failure of lithium batteries.The inhibition effects of different inhibitors on the temperature of single and multi-cell lithium batteries were as follows:CO₂-fine water mist>N₂-fine water mist>fine water mist>CO₂>N₂,and the inhibition effect for single cell and multi-cell battery CO₂-fine water mist was the best.For the thermal failure process of multi-section lithium battery,fine water mist,CO₂-fine water mist and N₂-fine water mist can inhibit the heat transfer in the thermal failure process of battery,and reduce the thermal failure transmission.