The Experimental Study On Thermal Characteristics And Thermal Safty For Power Lithium-ion Batteries

With the rapid development of global economy,the environmental problem is becoming more and more serious.The energy demand has become higher and higher.Because of the advantages of high energy density,long service life,high voltage level,environmentally friendlyness of the lithium-ion battery,it has been widely used in many industries.However,the problems such as the thermal runaway and thermal safety hindered the large scale application,industrialization and commercialization of the lithium-ion battery.Thereby,the researches on the thermal characteristics and safety of the lithium-ion battery could help us adequately recognize the thermal mechanism and clearly understand the induced factors of thermal runaway of the lithium-ion battery at work.It will contribute to the improvement of the battery safety and provide the theoretical foundation for the optimal design of the battery pack.The thermotank and Adiabatic Accelerating Rate Calorimeter are used in this paper to analyze the thermal characteristics of the lithium-ion battery under the ambient and adiabatic conditions,respectively.The battery safety is compared at different capacities.The charging and discharging experiments of the lithium-ion battery are carried out in the thermotank to investigate the different factors affecting the thermal characteristics of the lithium ion battery.The results showed that the greater the charge and discharge rates were,the higher battery temperature and the greater heat generating capabilities could be obtained.The same conclusions were reached at the lower state of charge and environmental temperature conditions.Because of the cell in the middle of the battery pack is mostly at adiabatic condition,it has more thermal hazard.The charging and discharging experiments of the lithium-ion cell are investigated by using the Adiabatic Accelerating Rate Calorimeter.The results showed the greater the charge and discharge rates were,the faster the voltage and temperature rise rates would be.The lower the state of charge was,a higher charge temperature and a lower discharge temperature could be obtained,but a higher change rate of temperature in the discharge process could be found.The higher the initial temperature was,the higher the battery temperature could be,but a lower change rate of temperature could be found.The specific heat capacity test of a 20 Ah LFP battery was studied and then the quantity of heat release under the adiabatic condition in the charge and discharge process was calculated.In practice,battery capacity decreases and performance decays with the increase of service time.The characteristics such as voltage and temperature of the different spent batteries were compared at various service times with.The specific heat capacity test of a 83 Ah LFP battery was studied.The results showed that the residual capacity and specific heat capacity of the battery were decreased with the increased service time.It would lead to the decrease of the thermal runaway temperature and the deterioration of the battery safety.