Studies On Combustion Characteristics Of Lithium-ion Battery Components And Flame-retardant Improvement Measures Of Electrolytes

Lithium-ion batteries are favored for advantages such as high energy density,long cycle life,and no pollution to the environment.Now,they are widely used in many industries.Lithium-ion batteries are composed of a variety of active materials,including positive and negative electrodes,separators,and electrolytes.Due to the improper use of these components,it is easy to cause thermal runaway.Direct combustion or combustion will occur,resulting in fire and explosion accidents of lithium ion batteries,which pose a great threat to the safe use of lithium ion batteries.The research on the hazard of lithium-ion battery can master the combustion characteristics and the law of fire occurrence.The results can provide a reference for the safe design of lithium-ion batteries.Based on the experimental study on the mixed combustion of lithium ion battery components,the combustion characteristics of binary and ternary carbonate mixed solvents are analyzed,and the fire hazard differences of the mixed system formed by carbonate solvents,lithium salts and separators are studied.The results show that the combustion of carbonate mixed solvents is affected by the elemental components.Generally,the chain carbonate solvent is preferentially burned,and then undergoes the component conversion phase,and the cyclic carbonate solvent begins to dominate the combustion.The lithium salt will reduce the average effective heat of combustion of the mixed system due to the endothermic effect.At the same time,the decomposition of the lithium salt will produce the toxic gas hydrogen fluoride,which will increase the threat of the mixed system and lead to more serious accidents.The exothermic reaction of the separator will lead to a higher effective combustion heat of the mixed system,which inevitably increases the fire risk,and the separator has different effects on the combustion of different carbonate solvents.In addition,the effective combustion heat of the mixed system formed by the lithium salt,the separator and the carbonate solvents are small,indicating that there is a competition between the endothermic reaction of the lithium salt and the exothermic reaction of the separator.The endothermic effect of the lithium salt on the mixed system is greater than the exothermic effect of the separator.In view of the flammability characteristics of lithium-ion battery electrolytes,this paper studies the effect of three composite flame retardants used in the electrolyte and carbonate solvents.The effect of lithium salt on the flame-retardant effect of carbonate solvents is explored,and the combustion process of samples is analyzed in detail.The results show that the lithium salt has a greater influence on the flame-retardant effect of the carbonate solvent,changing the burning rate and flame shape of the carbonate solvents.The burning rate of carbonate solvents containing flame retardants was reduced to varying degrees,and the flame state of samples also changed greatly due to the addition of flame retardants.Phenoxycyclophosphazene greatly reduces the peak value of the burning rate of carbonate solvent,and reduces the height of the flame and the peak temperature of the fuel,but does not change the flame temperature.Melamine phosphate reduces the burning rate of the low-boiling component control stage,and reduces the height of the flame and the peak temperature of the fuel,but does not change the peak temperature of the carbonate solvents flame.Tris(2-chloropropyl)phosphate has the best effect,because it not only greatly reduces the burning rate of carbonate solvents,but also reduces the peak temperature of flame and fuel,which significantly improves the safety of carbonate solvents.