Study On Aging Mechanism And Thermal Safety Of Lithium Cobalt Oxide Battery In Low Pressure

With the increasing demand for global energy and environmental protection,the research and commercialization of electric aircraft has attracted much attention,and the development of new and renewable energy is a key link.Among these new energy sources,lithium-ion batteries have been developed rapidly because of their good comprehensive performance.However,the further application of electric propulsion has been restricted by the recession of performance due to the problems of aging and thermal safety in its whole life with the improvement of energy density for power lithium-ion batteries.Therefore,it is of great significance to study the thermal safety of aging batteries in low pressure environment for the safety prevention and control of aviation lithium-ion batteries.In this thesis,the cyclic aging experiments and thermal runaway experiments of lithium cobalt oxide pouch lithium-ion battery under low pressure are carried out.The research mainly investigates the aging mechanism and thermal runaway characteristics of lithium-ion battery under different atmospheres,low pressure with different discharge multiplier and different cycle times coupled aging path.The experimental results show that:（1）The electrochemical performance of the aged battery decreased gradually under low pressure environment.Due to the change of the mechanical stress of the battery in the low pressure environment,the contact of the active material is deteriorated,the loss of active lithium ion is increased,and the side reaction in the inner layer of the battery is intensified.As the ambient pressure decreases from 96 k Pa to 30 k Pa,the reversible lithium decay increases by26.6%and the lithium plating side reactions advance by 25.0%in 50 cycles,and the battery health state declines sharply.The battery T_onset decreases by 14.5°C under adiabatic environment,and the aging battery material and safety stability declines significantly under low pressure.（2）The aging rate of the battery varies according to the stress type,and the aging rate increases with the increase of discharge multiplier and the decrease of pressure,but the low pressure accelerates the aging effect of the battery significantly.As the pressure decreases and the multiplicity increases,the battery under the coupled aging path decays faster due to the significant increase in the loss of active lithium ions and positive active material during the charging process,and the irreversible lithium plating side reactions intensify and occur earlier.The thermal runaway temperature T_TR decreases,the heat production decreases,the thermal runaway intensity increases and the thermal stability of the battery decreases under the coupled aging path.Battery safety state fades to 58.891%at 2.0 C aging condition at 30 k Pa.（3）The battery capacity decays with the increase of cycle times.As the ambient pressure decreases from 96 k Pa to 30 k Pa,the battery capacity decay increases between different cycle times,and the low pressure is the decisive stress for the increase of battery aging rate.As the pressure decreases and the cycle number increases,the loss of active lithium ions and anode active material increases during the charging process of the battery under the coupled aging path,and the irreversible lithium plating side reactions intensify and occur earlier.The battery thermal runaway time under the coupled aging path is advanced,the flame injection intensity increases,the thermal runaway heat production decreases,and the thermal stability decreases.50 and 100 cycles of aging conditions under 30 k Pa sharply decrease the battery thermal safety state to 35.01%and 21.02%,respectively.