Study On Thermal Runaway Propagation And Early Warning Of Lithium Ion Power Batteries

As one of the strategic emerging industries vigorously cultivated and developed in China’s "13th five-year plan" and "made in China 2025",the safety of lithium ion power batteries,one of the "three power" systems of new energy vehicles,has attracted extensive attention from all sectors of society.Due to the change and guidance of national policies,the specific energy of power batteries is expected to reach 300wh/kg after 2020,At the same time,the battery safety performance has also encountered a severe test.Among the safety requirements of lithium ion batteries,the problem of heat runaway and diffusion is particularly prominent.Due to the complex out-of-control characteristics of lithium ion batteries,especially ternary lithium batteries,different structural design of different battery packs,research progress in the current stage is slow and usually limited to the study of monomer thermal out-of-control in the field of electrochemistry,and the problem of thermal out-of-control diffusion is rarely studied.In addition,poor reproducibility often exists in the heat loss control experiment triggered by acupuncture of battery packs,which makes it difficult to obtain repeated and representable experimental data and restricts the research on the mechanism and prediction warning.The research on the runaway diffusion mechanism and early warning of battery heat is not only the crux that the host manufacturers must overcome,but also the crucial issue in the research and development of domestic standards for electric vehicle energy storage devices.Under the background and premise mentioned above,this paper provides a method to evaluate and warn the thermal runaway and diffusion path of selected battery pack when the specific mechanism and theoretical research are not enough.The thermal safety performance of the battery pack and the battery module was analyzed by means of experiment and simulation.Finally,the diffusion mechanism was revealed by means of data processing and fault tree,and the warning of thermal runaway was given.The specific research and experimental work is as follows:1.Fault tree analysis(FTA)of thermal runaway diffusion in battery system.Through fault tree qualitative and quantitative research,this paper analyzed the structural importance of factors and given suggestions for improving thermal diffusion.After that,the key research contents of precise prevention and early warning are determined.2.Analyzed and selected the experimental methods of triggering thermal runaway.3.This paper was proposed a thermal runaway diffusion model in battery pack and makes a simulation study on it.In order to obtain the simulated loading data,an acupuncture thermal runaway experiment of lithium-ion battery module was designed and carried out.The order of thermal runaway transfer in the model was analyzed through simulation.This lays the foundation for the thermal runaway experiment of battery pack,and verifies the positive role of the barrier in preventing thermal diffusion and inhibiting thermal runaway chain reaction.4.Based on the above research,six experiments and data processing of acupuncture thermal runaway for battery pack were carried out.In many experiments,there is a big problem of randomness in the measured data.This paper is deduced an uncertainty calculation method based on statistical principle.On this basis,the expected and confidence intervals of thermal diffusion time of the battery system are estimated.This method is verified by experiments and the heat-transfer-time has great significance for early warning.