Thermal Runaway,Propagation And Deflagration Characteristics Of Ternary Lithium-ion Battery Under Different Air Pressure

Over the past few years,the development of lithium-ion batteries has rapidly progressed due to their exceptional properties such as high energy density and long cycle life.As a result,the applications of these batteries has expanded from electronic products,energy storage power stations and electric vehicles to the aerospace industry.Among them,the main power system of all-electric aircraft and battery transportation of civil aviation are the main application scenarios of lithium-ion batteries in the aviation field.However,due to the inherent property of lithium-ion battery’s own composition material is flammable,resulting in its thermal runaway under abusive conditions,fire accidents caused by thermal runaway in aircraft have occurred occasionally in recent years.In order to solve the problems affecting the development of the battery industry,extensive research has been conducted on the thermal runaway characteristics and the intrinsic mechanism of batteries.However,there is limited investigation on their behavior during high-altitude flights and the influence of environmental pressure on the thermal runaway process.Therefore,the master thesis systematically studied the thermal runaway and propagation characteristics of lithiumion batteries in aerospace scenarios are from the single battery to the module level through a combination of experiments and simulations.(1)The thermal runaway characteristics of lithium-ion battery under different initial pressures are revealed.Based on the self-made lithium-ion battery pressure test bench,the thermal runaway experiments of commercial 18650 type Li(NixCoyMnz)O2(NCM)ternary lithium-ion battery under four initial pressures of 20kPa,60kPa,80kPa and 101kPa were carried out to reveal the influence mechanism of the initial pressure on the thermal runaway hazard of lithium-ion battery.The results show that the thermal runaway hazard of lithium-ion battery is positively correlated with the initial pressure,and the maximum thermal runaway temperature,heat release,mass loss and thermal runaway gas generation overpressure of battery all increase with the increase of initial pressure.The main components of the battery thermal runaway gas production are not affected by the initial pressure,and the gas production explosion limit range increases with the increase of the initial pressure.The mechanism of the initial pressure on the thermal runaway characteristics of the battery is further analyzed.The change of pressure affects the opening time of the battery safety valve,which further affects the exothermic reactions with electrolyte participation,while the absolute oxygen concentration affects the redox reactions involving oxygen which includes combustion reactions during the thermal runaway process of the battery.(2)The thermal runaway propagation laws of lithium-ion battery modules under different environmental pressures are revealed.Based on the variable pressure and oxygen concentration simulation bench,thermal runaway propagation experiments of 2×3 module commercial 18650 type NCM ternary lithium-ion batteries were carried out to compare and analyze the thermal runaway propagation behavior of the battery modules under four environmental pressures,and to quantitatively analyze the heat transfer mode between cells in the thermal runaway modules.The results found that reduced environmental pressure inhibited the thermal runaway propagation speed,heat release and combustion phenomenon of the battery module.The main heat transfer modes of the the thermal runaway battery inside the module are different under different environmental pressures.Under the environmental pressure of 20kPa and 60kPa,convective heat transfer is the main source of heat before thermal runaway of the target battery,while direct heat conduction between batteries due to surface contact is the main source of heat before thermal runaway of the target battery under the environmental pressure of 80kPa and 101kPa.(3)A model was established to evaluate the explosion risk of gas produced by the batteries in the interior scenario of an aircraft cargo compartment.Based on the analysis of the gas production components of the single battery in the thermal runaway experiments,explosion model of gas production of the batteries in cargo compartment of a narrow-body aircraft is established using finite element software to compare the explosion characteristics parameters such as maximum explosion temperature and maximum explosion overpressure of the battery gas production under different working conditions,and to evaluate the explosion risk of the mixture gas at different initial pressures and different concentrations of the gas produced by batteries.The simulation results show that the mixture gas had the strongest explosive power at a concentration of 35%of the gas produced by batteries at an ambient pressure of 101kPa.