| Under the background of global low-carbon development,lithium-ion batteries are gradually becoming an important cornerstone of the new energy industry with their advantages of high energy density and long cycle life,and are widely used in new energy vehicles,energy storage power stations,aerospace and other fields.However,in recent years,fire accidents caused by the thermal runaway problem of lithium-ion batteries have occurred frequently,especially in the fields of new energy vehicles and energy storage power stations,which have brought great harm to people’s lives and property safety.The safety issue of thermal runaway has become a technical bottleneck that restricts the development of the lithium-ion battery industry,and it is also one of the problems that need to be overcome urgently in the field of lithium-ion safety.This doctrol thesis systematically studied the thermal runaway and thermal runaway prevention and control problems of lithium-ion batteries from the battery to module level.Firstly,the thermal runaway heat-gas production characteristics of lithium-ion battery batteries were studied through thermal runaway experiments triggered by local overheating.The effects of state of charge and heating power on thermal runaway heat-gas production of lithium-ion batteries were revealed,and some typical behavioral characteristics such as thermal runaway jet fire and intense combustion of lithium-ion batteries were summarized.The change relationship between the energy required to trigger thermal runaway,the total heat production of thermal runaway and the stored electrical energy of the battery were clarified.The characteristics of thermal runaway propagation time inside single batteries were found to be extended with the decrease of state of charge and the increase of heating power,which lays a foundation for the subsequent research on the internal thermal runaway spread characteristics of single batteries.Secondly,the dynamic evolution law and the master control mechanism of the lithium-ion battery batteries’ thermal runaway fire was studied.Based on the image recognition algorithm and nonlinear fitting method,the Richardson number reflecting the combustion master control mechanism was obtained,which was used to reveal the master control mechanism of thermal runaway fire of ternary and lithium iron phosphate batteries.The influence of electrode materials and state of charge on the dominant mechanism of thermal runaway fire was quantified,and the geometric characteristics of thermal runaway turbulent diffusion flame were summarized.Then,the spread law and mechanism of local thermal runaway reaction inside the lithium-ion battery were studied by experimental and numerical method.Firstly,the spread characteristics of local thermal runaway reaction in different directions inside the battery and the corresponding voltage response were revealed through thermal runaway experiments under different heating positions.The mechanism of thermal runaway propagation inside the battery dominated by heat conduction was discovered,and a theoretical formula was proposed to qualitatively describe the propagation speed of thermal runaway inside the battery.A three-dimensional thermal runaway dynamic propagation model of a single battery with good agreement with the experiment was established,and the influence mechanism of heating power and battery thermal conductivity on the internal thermal runaway spread of the battery was systematically analyzed.It was found that the width of the thermal runaway region along the thickness direction widens with the decrease of heating power and the increase of thermal conductivity when the battery was in a critical thermal runaway state.It was verified that the battery with faster internal thermal runaway propagation had a higher peak gas injection speed.Furthermore,the thermal runaway propagation characteristics and mechanism of lithium-ion battery modules were studied.By introducing a failed battery without self-generated heat into the module,the self-generated heat of the battery during thermal runaway propagation was quantified for the first time.A new mechanism of thermal runaway propagation of modules under the combined action of battery self-generated heat and external heat transfer was revealed.The influence characteristics of electrical connection mode,trigger mode,electrode material,capacity and other factors on the thermal runaway propagation behavior of the module were studied,and the characteristic parameters such as temperature,voltage response,thermal runaway propagation time,heating power and other characteristic parameters during the thermal runaway propagation of the module were clarified.A three-dimensional dynamic of thermal runaway propagation model of modules was established,and the effects of local heating power on the module’s thermal runaway propagation were studied.Finally,aiming at the thermal runaway fire hazard of lithium-ion batteries and modules,a novel thermal runaway suppression strategy based on liquid nitrogen was proposed.The effectiveness of liquid nitrogen in inhibiting thermal runaway and its propagation was verified experimentally.By carrying out the experiment of inhibiting thermal runaway of small-format batterys by liquid nitrogen,the critical suppression temperature of liquid nitrogen to suppress battery thermal runaway was proposed.The delay performance and cooling performance of liquid nitrogen against irreversible thermal runaway were quantified,and the liquid nitrogen cooling mechanism dominated by membrane boiling heat transfer and radiant heat transfer was revealed.Furthermore,the effectiveness of liquid nitrogen in inhibiting thermal runaway propagation of large and small format battery modules was verified experimentally.The critical suppression temperature of liquid nitrogen to suppress thermal runaway propagation of modules was proposed,and the typical scenarios of liquid nitrogen suppressing module’s thermal runaway propagation were discussed. |
PDF Full Text Request