Research On Thermal Runaway Behavior Of Lithium-Ion Batteries

Lithium-ion batteries have excellent electrochemical performance and high energy density.As the power source of Electric Vehicles,its on research safety is very important,especially the thermal runaway problem of lithium ion batteries has been concerned.This dissertation uses battery adiabatic calorimeter to explore the thermal runaway of cylindrical high energy density 21700 lithium-ion batteries with different state of charge(SOC),Atom Layer Deposition(ALD)coating graphite anode batteries and polymer solid-state batteries.Using the differential scanning calorimetry and thermogravimetric analyzer to analyze the thermal stability of the internal materials of the battery.Scanning electron microscope was used to observe the microstructure of the separator and the cathode and the anode.besides the influence of the structure and properties of the material on the safety of the battery was analyzed.(1)The results of high energy density cylindrical 21700 lithium ion batteries show that the higher state of charge for the cylindrical lithium ion batteries,the lower the initial temperature point of side reaction,the lower the initial temperature of thermal runaway,and the higher the peak temperature of thermal runaway.The higher the charge,the higher the temperature rise rate,the more intense the reaction and the more mass loss.(2)The reaction between the anode interface and the electrolyte is slowed down by the coating layer on the surface of the anode graphite coated by ALD,which significantly reduces the side reactions of the battery during high temperature and greatly improves the cycle stability and thermal safety of the batteries.(3)Research on polymer solid-state batteries shows that : The coin batteries has less active substances,less self-heating,and the starting temperature of thermal runaway lags behind.The temperature–time(T–t)curve can clearly show the self-heating side reactions in the heating process of the battery.Separator melting is not the origin of thermal runaway,the heat released by battery short circuit will aggravate the occurrence of side reactions,The origin for thermal runaway is the reaction between electrode materials and electrolyte.The thermal runaway trigger mechanism of solid-state battery is that the cathode material releases oxygen at high temperature,and then reacts with the polymer and molten lithium for redox reaction.