Experimental Study On Heat Generation And Thermal Induced Runaway Of Lithium-ion Battery

Lithium ion battery is one of batteries,which storages energy to chemical energy,which has been used more and more widely using since its commercialization in 1991.It becomes the main power source of electric products,electric vehicles(EV),energy storage power stations,submarines,satellites,et al.The number of used batteries has shown an exponential growth tendency.Explosions and fire accidents of lithium ion battery are always reported as the increasing number of using batteries,which makes lithium-iqn battery safety has attracted more and more attention.The main point of this thesis is to study the characteristic of heat generation during working and thermal induced runaway of lithium ion battery with ternary cathode material.In first part,the heat generation of lithium ion battery was studied by using isothermal battery calorimeter(IBC)(THT Inc.,UK),which could provide a isothermal temperature under the range from-10 0C to 80 °C,and in situ measure the heat generation rate of battery during charge and discharge cycles.Effects of current and temperature on heat generation during charge and discharge processes were studied.The heat generation increases during both charge and discharge processes as the operating current increasing,and decreases during both processes as ambient temperature increase from 10 °C to 55 °C.The battery can work well under temperature no larger than 80°C.After temperature exceeding 80?,the internal material of the battery begins to decompose and the battery performance degrades,which may cause failure of the battery.The separator starts to melt as temperature increasing beyond the melting temperature of separator,which leads an internal short circuit,and follows hazardous exothermic reactions.The influences of the ambient t teperature and the state of charge(SOC)on the direct current resistance(DCR)of the battery were studied.It was found that internal resistance decreased as ambient temperature increased,and decreased as SOC.The maximum resistance appears at low SOC stage.A 100%SOC cell was used to study the effect of temperature on resistance and the voltage temperature parameter,which were used to calculate the heat generation.By comparing the calculated result and the measured one,the calculated method can match the measured results well.In the third part,the thermal stability of internal materials were studied.Effect of SOC on thermal stability of anode and cathode was tested by using C80 calorimeter.The reaction heat of both anode and cathode increases as SOC increasing.The existence of electrolyte make more heat generation of both cathode and anode.A new method was used to study the difference between internal temperature and surface temperature by inserting a thermal couple into the test battery.The maximum temperature difference between inside and surface of battery is 14 ?under thermal induced condition.The thermal runaway time,maximum temperature and induced hazard were increasing as the SOC increasing under same thermal induced conditions.The 18650 battery has a thermal return temperature,which decreases as SOC increasing.The thermal return temperature of 100%is 160?,while the value becomes to 185? under 25%case.The effect of SOC on return temperature is more than 25?.The heat generation during normal working and thermal induced failure were studied.The irreversible and reversible heats are dominant during normal working state,while the reaction heat is dominant during high temperature conditions.Thermal induced runaway of lithium ion battery includes decomposition of SEI,reaction of electrolyte,decomposition of cathode and anode.The heat generation of internal reaction between electrolyte and cathode/anode is dominant under large SOC case.