Application Of Phase Change And Thermochemical Heat Storage Of A Salt Hydrate For Battery Thermal Management And Thermal Runaway Prevention

The performance and safety of lithium-ion batteries are significantly affected by temperature.Under the normal operation and extreme abuse condition,the temperature of battery pack cannot exceed 55℃and 120℃,respectively.Otherwise,a high temperature will cause the performance degradation,and even trigger battery thermal runaway with serious accidents such as fire and explosion.Therefore,the batteries have a demand for thermal management in a large temperature range.Inorganic salt hydrate is a kind of phase change material with low cost,environmental friendliness and non-flammability.More importantly,it has both phase change heat storage capacity and thermochemical heat storage capacity,which makes it become a promising heat storage material in the phase change battery thermal management system.In this paper,a sodium acetate trihydrate-urea/expanded graphite（called SAT-Urea/EG for short）thermal storage material meeting the battery thermal management requirements was prepared.This material has a phase transition enthalpy of 181.0 J/g and a thermal decomposition enthalpy of 567.3 J/g at 58℃and 114℃,respectively.It can meet the battery thermal storage requirements in the working temperature range of-20℃～60℃and in the thermal runaway section of 90℃～120℃,respectively.The super-cooling degree of this material is reduced to 1.4℃,and the thermal conductivity is as high as 4.96 W·m^-1·K^-1,which is conducive to improving the temperature uniformity in the batteries pack.In addition,this salt hydrate phase change material exhibits an excellent flame retardancy which can improve the safety of the battery thermal management system.At a heat flux of 35 k W/m²,its total heat release is only 0.79 MJ/m².After the microporous sealing of expanded graphite and the macroscopic sealing of potting adhesive,the stability of this composite has been greatly improved.After 100 thermal cycles,the latent heat only decreases by 6.9%,which is beneficial to the long-term use of the material in battery thermal management.The SAT-Urea/EG composite material exhibits good thermal management effects and cycling temperature control performance.Under the normal charge and discharge conditions,thanks to the phase change thermal storage capacity of SAT-Urea/EG,the temperature of the pack with 20 batteries even at 2C discharge rate were successfully controlled within safe operating range.In the extreme case of battery external short circuit,the composite can reduce the risk of thermal runaway.In the battery thermal runaway situation,thanks to the thermochemical heat storage capacity of SAT-Urea/EG,the time to reach the thermal runaway trigger temperature of 120℃is successfully delayed by 2～3 min,which significantly slows down the occurrence of thermal runaway.Therefore,the dual-temperature thermal storage capacity of the salt hydrate composite phase change material has great research significance and value of popularization and application in battery thermal management.