新能源汽车动力电池组热失控的连锁反应机制、临界判据及液氮抑制机理

Lithium-ion battery thermal stability limits the development of new energy vehicles. Vehicle lithium-ion battery sometimes exists in confined space, with high temperature and high rate charge and discharge. Under this condition thermal runaway of the battery pack might occur, leading to serious leakage, fire and explosion accidents. This is due to thermal runaway propagation of lithium-ion battery pack. Chain reaction mechanism and inhibition mechanism for thermal runaway of battery pack are very important scientific problems. In this project, the research idea of "mechanism revealing, modeling and simulation, methods presenting" is put forward to study thermal runaway propagation of lithium-ion battery pack. The field investigation, theoretical modeling, experimental research, image processing, theory analysis and case analysis and validation are used to carry out the following research: (1) To study the hazards and the characteristics of thermal runaway propagation for battery pack, and to study the influencing factors and occurrence conditions, and then to reveal the chain reaction mechanism; (2) To investigate the critical criterion of thermal runaway spreading for the battery pack, and to find out the rule of energy transmission during the thermal runaway process, and then to build the energy transfer calculation model and the prediction method for the thermal runaway propagation of battery pack; (3) To research on the effect of liquid nitrogen on the thermal runaway propagation for battery pack, and to find out the inhibition mechanism, and then present an effective way to inhibit the spread of the thermal runaway by using liquid nitrogen. Cooling and smothering effect for lithium-ion battery thermal runaway propagation is studied. The research results can provide theoretical basis and technical support for the design, storage, use and management for the power battery pack of new energy vehicle.

锂离子电池组热稳定性是制约新能源汽车发展的瓶颈，汽车动力电池出现在受限空间、高温和高倍率充放电等条件下的几率越来越大，极易导致电池组热失控传播引发泄漏、燃烧甚至爆炸事故。针对热失控连锁反应机制和抑制机理的关键科学问题，开拓性地提出电池组热失控“机理认识—模型建立—方法构建”的研究思路。本课题采用现场调研、理论建模、实验研究、图像处理、理论分析、案例分析和验证等多种手段开展以下研究：（1）研究电池组热失控危险特性、热失控传播影响因素及其发生条件，揭示连锁反应机制；（2）研究电池组热失控传播的临界判据，寻找能量传递规律，建立热失控能量传递计算模型和热失控传播预测模型；（3）研究液氮对电池组热失控传播的影响规律及其抑制机理，构建冷却和窒息作用较强的液氮抑制方法。研究结果为新能源汽车动力电池组的设计、储存、使用和管理提供理论依据和技术支撑。

随着国家对新能源产业的重视，锂离子电池应用愈加广泛，新能源汽车正式步入高速发展时代。但近年来，因锂离子电池组在受限空间、高温和高倍率充放电等条件下极易导致热失控传播引发泄漏、燃烧甚至爆炸事故，成为了新能源汽车发展的瓶颈。因此，项目基于电池组热失控“机理认识—模型建立—方法构建”的研究思路，研究了新能源汽车动力电池组热失控的连锁反应机制、临界判据及液氮抑制机理。开展了电池组热失控危险特性、热失控传播影响因素及其发生条件；电池组热失控传播的临界判据，能量传递规律，热失控能量传递计算模型和热失控传播预测模型；液氮对电池组热失控传播的影响规律及其抑制机理等方面的研究工作。最终，揭示了锂离子电池热失控及传播机理和抑制规律。建立了50℃、100℃、120℃三级热失控预警温度；研究了热失控产气过程及其气体成分变化规律；探索了液氮对热失控的影响机制，提出了电池组内过热单电池定位及报警方法，建立了热失控过程的温度和气体安全预警方法。研发了热失控主动防控技术，自主研制了的石蜡、膨胀石墨、活性炭质量比率为20：4：1的一级复合相变材料和聚乙二醇1500、甲基纤维素质量比率为1.5：1的二级复合相变材料，实现了电池热失控初期的温升抑制；并提出了相变材料用量计算方法。开发了液氮降温灭火技术，明确了以0.04MPa出口压力对锂离子电池进行喷淋液氮降温或灭火，可迅速降温或灭火并抑制复燃。基于上述成果，结合红外温度监控、视频监控、火焰报警、微信报警等技术，集成开发了热失控预测预警与主动防控系统，研究结果为新能源汽车动力电池组的设计、储存、使用和管理提供理论依据和技术支撑，项目成果具有较好的应用推广前景。