基于膨胀石墨/石蜡相变复合材料的锂离子电池热管理系统研究

The vast heat produced during the operation of lithium ion batteries will rise the internal temperature of batteries, induce the uneven distribution of heat, shorten the cycle life of batteries and even cause thermal runaway. Therefore, the research of thermal management of lithium-ion batteries has an important significance. Expanded graphite/ paraffin composite phase change materials (EG/PCM) has been the research hotspot of lithium-ion battery thermal management (BTM). In view of the insufficiency of existing research situation, the following research work will be scheduled to be carried out. Firstly, researches about heat generation rate and thermophysical properties of lithium-ion battery will be carried out. These researches will reveal the connection between lithium-ion battery heat generation rate and battery temperature, state of charge (SOC) under different charging and discharging rate conditions. Secondly, integration and experiment research of lithium-ion BTM using EG/PCM composites will be carried out. The effect of single BTM performance and content of EG will be revealed. The EG/PCM with peak heat dispersion will also planned to be carried out with battery module experiment research. The impact of phase change cooling on uniformity of battery heat dispersion will be studied. The experiment and simulation results will be compared with each other to support the simulation model of estimation. Lastly, in according with test results of heat generation rate, simulation of lithium-ion BTM based on EG/PCM will be carried out. A mathematic model based on flow and heat transfer in porous media will be established for simulation of phase change heat transfer process. This research will reveal the phase change heat transfer mechanism, heat transfer in porous media mechanism, and coupling mechanism of fluid flow and phase change heat transfer.

锂电池在使用时会产生大量热量，导致电池温度升高及电池组内温度不均匀，降低其循环寿命，甚至会引起热失控。因此对其进行热管理非常重要。膨胀石墨/石蜡(EG/PCM) 相变冷却是锂电池热管理(BTM)的研究热点。针对目前研究不足，本项研究拟开展以下工作。首先开展锂电池生热功率和热物性研究，揭示不同充放电工况下锂电池生热功率随电池温度、荷电状态变化的规律。其次开展EG/PCM锂电池BTM的集成及实验研究，针对单体电池开展不同膨胀石墨含量PCM对锂电池BTM性能的影响规律，最佳散热性能膨胀石墨比例的EG/PCM再开展电池模块实验研究，考察相变冷却对电池组散热均匀性的影响；实验结果与模拟结果进行对比、分析，为模拟模型的建立提供支持。最后根据生热功率测试结果开展EG/PCM锂电池BTM模拟研究，采用相变物质在多孔介质中流动传热模型，揭示相变传热机理、多孔介质传热机理、流体流动和相变传热耦合机理。

锂电池在使用时会产生大量热量，导致电池温度升高及电池组内温度不均匀，降低其循环寿命，甚至会引起热失控。因此对其进行热管理非常重要。膨胀石墨/石蜡(EG/PCM)相变冷却是锂电池热管理(BTM)的研究热点。针对目前研究不足，本项研究开展了以下工作。首先开展了锂电池和相变复合材料的热物性研究，其次集中电池模型用来生成适当的热源，然后将这些热源与多孔介质传热，相变传热进行耦合。集总电池模型，需要锂离子电池的容量，锂离子电池不同荷电状态的开路电压，不同荷电状态下的电池的温度导数，电池的欧姆过电位，浓度过电位及活化过电位等参数。相变复合材料热导率与纯的相变材料相比，提高了17-88倍。根据锂离子电池生热模型耦合相变传热模型研究得出，经过两个充放电循环，用相变复合材料来对锂离子电池进行热管理，能显著降低锂离子电池温度。与空气冷却相比，相变复合材料冷却下的锂离子电池温升能降低至少6℃左右。相变复合材料用于锂离子电池系统的冷却系统，特别是瞬态的大功率散热都具有很大的优势，而且不用设置额外的主动冷却系统来增加额外的动力消耗。该项目揭示了锂离子电池生热机理、相变传热机理、多孔介质传热机理、以及它们的耦合传热机理。