动力电池热行为及其过热性分析

发布时间：2018-08-08 19:42

【摘要】：动力电池作为电动汽车的核心技术,其动力性与经济性的改善和提升一直都是研究重点,但是受冷却结构、材料以及布置空间与使用条件的限制,容易导致电池在工作中产热累积而引发热安全问题,显然,这已成为了限制动力电池可持续发展的技术瓶颈。因此,亟需开展关于动力电池在不同工况条件下的热力学—电化学特性行为的研究,从本质上了解和掌握电池的工作性能,有助于分析和预测电池的热行为,并为电池热管理设计与相关控制策略提供合理可靠的参考依据。本文分析了锂离子单体电池在正常放电条件下、内部短路以及高温环境下三种不同机制工况条件下的产热特性和荷电特性。首先基于电池电化学机理,建立了片状锂离子电池单体的物理模型,分析了电池温度场、内部电流分布、电化学热以及焦耳热的变化机理,建立了更加系统全面的锂电池仿真分析。锂电池单体正常放电条件下的仿真结果表明:在绝热环境下,电池放电倍率直接影响电池单体的平均温升速率和温匀性。随着放电倍率的增大,电池温升速率增加,温度均匀性变差。在绝热环境下,电池初始温度直接影响电池单体的温均性,初始温度越低,电池单体的温均性越差,当初始温度较高时,电池平均温升速率增加,电池工作温度很快超出合理的工作范围。荷电状态的不同也会影响电池平均温度的变化,荷电量较少的电池,其温度升高速率越快。通过分析与总结诸如短路深度、短路位置、短路截面积以及荷电状态等不同因素对锂离子电池单体工作特性的影响规律,得出如下结论:随着短路深度的增加以及短路截面积的增大,短路区域的最高温度以及最大电流会随之增大。相比于电池中心部位发生内部短路,当电池边缘区域发生内部短路时,短路区域的最高温度显著增加。另外,当电池发生内部短路时,随着电池的荷电量增加,电池短路区域最高温度随之升高。在内部短路发生过程中,放电倍率对电池短路区域最高温度影响作用较小。最后,本文建立了电池置于高温环境下的热滥用模型,分析了温度变化和表面对流传热系数变化对电池单体特性的影响。仿真结果表明:当电池在较低的环境温度下工作时,电池单体仅体现出温升特性,并不会触发电池内部各材料的分解副反应;当环境温度到达某一个高温点时,电池会出现急剧的温升现象,即触发了电池内部材料分解的热失控副反应;随着环境温度的升高,电池内部材料分解的热失控副反应的触发时间点会提前。另外,在高温环境下,电池表面等效传热系数较低时有利于抑制电池热失控反应的发生;而较高的电池表面等效传热系数,会使电池热失控状态提前触发。
[Abstract]:As the core technology of electric vehicles, the improvement and upgrading of power performance and economy is always the focus of research, but it is limited by cooling structure, materials, layout space and use conditions. It is easy to cause thermal safety problems due to the accumulation of heat in battery production. Obviously, this has become the technical bottleneck that limits the sustainable development of power battery. Therefore, there is an urgent need to study the thermodynamics and electrochemical characteristics of power batteries under different operating conditions, to understand and master the working performance of the batteries in essence, and to help to analyze and predict the thermal behavior of the batteries. It also provides reasonable and reliable reference for battery thermal management design and related control strategies. In this paper, the thermal and charging characteristics of Li-ion single cell under normal discharge, internal short circuit and three different operating conditions of high temperature mechanism are analyzed. Firstly, based on the electrochemical mechanism of the battery, the physical model of the single cell was established, and the variation mechanism of the cell temperature field, internal current distribution, electrochemical heat and joule heat was analyzed. A more systematic and comprehensive simulation analysis of lithium battery is established. The simulation results show that under adiabatic environment, the discharge rate of lithium battery directly affects the average temperature rise rate and temperature uniformity. With the increase of discharge rate, the temperature rise rate increases and the temperature uniformity becomes worse. In adiabatic environment, the initial temperature of the cell directly affects the temperature homogeneity of the cell. The lower the initial temperature, the worse the temperature uniformity of the cell. When the initial temperature is high, the average temperature rise rate of the cell increases. The battery temperature quickly exceeds the reasonable working range. The change of the average temperature of the battery is also affected by the different state of charge. The faster the increase rate of the temperature is when the charge is low. By analyzing and summarizing the influence of different factors such as short circuit depth, short circuit position, short circuit cross section and charge state on the performance of lithium ion battery, The conclusions are as follows: with the increase of the short circuit depth and the short circuit cross section, the maximum temperature and the maximum current in the short circuit region will increase. Compared with the inner short circuit in the center of the battery, the maximum temperature of the short circuit region increases significantly when the inner short circuit occurs in the edge region of the battery. In addition, the maximum temperature of the short circuit region increases with the increase of the battery charge. In the process of internal short circuit, the discharge rate has little effect on the maximum temperature in the short circuit region of the battery. Finally, the heat abuse model of the battery under high temperature is established, and the effects of temperature change and surface convection heat transfer coefficient on the cell characteristics are analyzed. The simulation results show that when the battery is working at a lower ambient temperature, the cell only exhibits the characteristics of temperature rise and does not trigger the decomposition side effects of various materials in the battery, and when the ambient temperature reaches a certain high temperature point, There will be a sharp temperature rise in the battery, that is, the thermal runaway side reaction of material decomposition in the battery will be triggered, and with the increase of the ambient temperature, the trigger time of the thermal runaway side reaction of the material decomposition in the battery will be advanced. In addition, at high temperature, the lower surface equivalent heat transfer coefficient of the battery is conducive to inhibit the occurrence of the thermal runaway reaction, and the higher surface equivalent heat transfer coefficient of the battery will trigger the heat runaway state of the battery ahead of time.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM912

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