Fire Risk And Thermal Analysis On The Overcharge Reaction Of Lithium Ion Battery

Due to its high voltage, high specific energy, long cycle life, no pollution to the environment and other excellent performance, Li-ion battery has become the dominant power in the field of consumer electronics. However, fire incidents caused by over charge of Li-ion battery have been reported recent years. Safety has become one of the most intractable barriers to the wide application of Li-ion battery in the above industry. Therefore, study on thermal runaway and fire hazard of Li-ion battery and high-safety battery system can improve understanding on the origins of thermal runaway and fire of the battery, clarify the main unsafe reason, determine the behavior and hazard of thermal runaway and fire quantitatively, and propose the safe battery system to reduce the possibility of the incidents, to provide data base and technical support for the battery safety and fire protection design.The work of this thesis are summarized as following:1)This thesis systematically introduced the development, working mechanism, and the composing of LIBs. In addition, it analyzed the essence of safety and thermal characteristics. The results can provide some guidance for the choice of good safety performance materials, and provide some theoretical advices to improve the stability of LIBs.2) Through the experiment of the overcharge reaction of LIBs, it can be obtained that the temperature change of the LIBs and the swelling, cracking of the LIBs, in these experiments FTIR and high-speed camera are be used to get related data and photo to analyze the fire and damage due to the overcharge reaction of LIBs3) On the actual analysis aspects, this thesis adopted ANSYS and computer simulation tools to construct a model on the hypothesis that the safety issues of LIBs can be indicated by heat generation to approach more accurate adiabatic thereto-characteristics of LIBs. Thesis explored inner temperature grad of cell by extending the research scale from small capacity portable communication power sources to medium capacity high power LIBs. Through rational module design and parameters input, the thesis got detailed results of thermal characteristics and comparisons. It also provides some guidance to improve safety performance of lithium ion batteries.4) Through using explosion theory and FTA, the thesis discussed the explosion mechanism, as well as providing safety using guidance and safety design. The fire behavior is studied systematically. On the basis of chemical dynamics and thermodynamics theory, thermal self-ignition theory, electrochemical theory, safety engineering theory and heat transportation theory. It also disclosed the heat-generating mechanism.