由于受能源危机和环境污染的双重压力，电动汽车成为当今汽车产业发展的趋势。锂离子电池作为电动汽车的动力来源，其具有比能量高、输出功率大、倍率性能优异、循环寿命长、安全性好等特点，但是随着电动汽车的发展，动力电池的热安全性问题日益突出。锂离子电池长时间循环使用过程中内部会产生大量的热，如果无法及时散去而积聚在内部，会使电池工作温度逐渐升高，而高温容易导致电池工作性能急剧下降及电池寿命衰减，严重时会引起着火甚至爆炸等安全性问题。因此，关于动力电池使用过程发热及散热特性的研究已经成为电动汽车设计领域的重要研究课题。本文首先基于电化学-热耦合模型，首先对磷酸铁锂单体电池和电池模组进行热特性研究，分析了电池产热及散热基本特征及主要影响因素；在此基础上建立了电池容量衰减模型，分析了不同温度下电池容量衰减的特征及规律；最后基于磷酸铁锂发热及散热特征，设计了电池模组液冷散热结构，并分析其对电池组温度场的影响规律，优化了液冷散热的参数及结构。具体研究内容如下：

（1）基于电化学-热耦合模型，建立了磷酸铁锂单体电池热仿真模型，研究了放电倍率、环境温度和交流换热系数对单体电池及电池组热特性的影响，分析了其对电池温度场的影响。结果表明：电池放电倍率、对流换热系数和环境温度对单体电池及电池组的温度场具有重要的影响，放电倍率越高，对流换热系数越大，电池温差越大，温度均匀性越差，高温和低温环境使电池温差变大，温度均匀性变差。

（2）基于电池负极SEI生长理论建立了磷酸铁锂单体电池容量衰减模型，研究不同温度条件下放电倍率、负极粒径大小和充电截至电压对电池容量衰减的影响，分析了温度对电池容量衰减过程的影响规律，结果表明：放电倍率、负极粒径及充电最大截至电压对电池容量衰减具有明显的影响，放电倍率越高，充电截至电压越大，电池容量衰减速度越快，负极材料的粒径变小可减缓容量衰减速率。温度升高将加快电池内部副反应的发生，使电池活性锂的降低，正负极材料结构破坏，金属离子溶出，最终导致容量衰减过程加速，降低其使用寿命。

（3）针对6个软包磷酸铁锂电池组，设计了板式和蛇形弯管液冷结构，分析了流体流向、流体入口温度和流体流速对电池组温度场的影响，结果表明：蛇形弯管散热系统降温效果优于板式散热系统，这是因为弯管结构使流体曲折回旋，避免进出口温度冷却效果差异，提高了电池组温度均匀性。

综上，本文对锂离子电池单体及电池组的热特性、容量衰减及液冷散热等关键问题进行了研究，探讨了热行为及容量衰减的影响因素，采用液冷散热方式对电池组散热并进行液冷性能优化，本文研究结果为电池安全使用提供理论指导，液冷散热优化结果为电池热管理策略的开发提供一定的参考，以便进一步保证动力电池的使用性能以及提高电池的热安全性。

Due to the dual pressure of energy crisis and environmental pollution, electric vehicles have become the development trend of today's automobile industry. As the power source of electric vehicles, lithium-ion batteries have the characteristics of high specific energy, large output power, excellent rate performance, long cycle life, and good safety. However, with the development of electric vehicles, the thermal safety of power batteries has become increasingly problematic. prominent. Lithium-ion batteries will generate a lot of internal heat during long-term cycling. If they cannot be dissipated in time and accumulate inside, the battery's operating temperature will gradually rise, and high temperature will easily lead to a sharp decline in battery performance and degradation of battery life. Sometimes it will cause safety problems such as fire or even explosion. Therefore, the research on the heating and heat dissipation characteristics of power batteries during use has become an important research topic in the field of electric vehicle design. Based on the electrochemical-thermal coupling model, this paper first studies the thermal characteristics of lithium iron phosphate single cells and battery modules, and analyzes the basic characteristics and main influencing factors of battery heat generation and heat dissipation; on this basis, the battery capacity attenuation is established The model analyzes the characteristics and laws of battery capacity attenuation at different temperatures; finally, based on the heating and heat dissipation characteristics of lithium iron phosphate, the liquid cooling structure of the battery module is designed, and its influence on the temperature field of the battery pack is analyzed, and the liquid is optimized. Parameters and structure of cooling and heat dissipation. The specific research content is as follows:

(1) Based on the electrochemical-thermal coupling model, a thermal simulation model of lithium iron phosphate single battery was established, and the effects of discharge rate, ambient temperature and AC heat transfer coefficient on the thermal characteristics of single battery and battery pack were studied and analyzed The impact on the battery temperature field. The results show that the battery discharge rate, convective heat transfer coefficient and ambient temperature have an important influence on the temperature field of single cells and battery packs. The higher the discharge rate, the greater the convective heat transfer coefficient, the greater the battery temperature difference, and the greater the temperature uniformity. Poor, high temperature and low temperature environment make the temperature difference of the battery become larger, and the temperature uniformity becomes worse.

(2) Based on the SEI growth theory of the negative electrode of the battery, the capacity decay model of lithium iron phosphate single battery was established, and the influence of the discharge rate, the size of the negative electrode size and the charge cut-off voltage on the battery capacity decay under different temperature conditions was studied, and the temperature on the battery capacity was analyzed. The influence law of the decay process, the results show that: the discharge rate, the negative electrode particle size and the maximum charge cut-off voltage have obvious effects on the battery capacity attenuation. The higher the discharge rate, the greater the charge cut-off voltage, and the faster the battery capacity decays. A smaller particle size can slow down the rate of capacity decay. Increasing temperature will accelerate the occurrence of side reactions inside the battery, reduce the active lithium of the battery, destroy the structure of the positive and negative electrodes, and dissolve metal ions, which will eventually accelerate the capacity decay process and reduce its service life.

(3) For 6 soft-packed lithium iron phosphate battery packs, the plate and serpentine elbow liquid cooling structure was designed, and the influence of fluid flow direction, fluid inlet temperature and fluid velocity on the temperature field of the battery pack was analyzed. The results showed that: serpentine The cooling effect of the elbow cooling system is better than that of the plate cooling system. This is because the elbow structure causes the fluid to twist and turn, avoiding the difference in the cooling effect of the inlet and outlet temperature, and improving the temperature uniformity of the battery pack.

In summary, this paper studies the thermal characteristics, capacity attenuation and liquid cooling heat dissipation of lithium-ion battery cells and battery packs, and discusses the factors affecting thermal behavior and capacity attenuation, and uses liquid cooling to dissipate heat from the battery pack. And optimize the liquid cooling performance. The research results of this paper provide theoretical guidance for the safe use of batteries. The optimization results of liquid cooling heat dissipation provide a certain reference for the development of battery thermal management strategies, so as to further ensure the performance of the power battery and improve the thermal safety of the battery.

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