三元/硅碳锂电池热-电特性交互关系及液冷板/高导热界面材料耦合热管理模型中的传热规律研究

In this project, with the aim of enhancing the thermal safety performance of NCA/Si-C power batteries in practical loading application, the relevance of electrochemical-thermodynamic characteristic parameters and heat transfer rules of composite conductive models referring to NCA/Si-C system is systematically and thoroughly researched, which will promote the thermal-safety rapidly improvement and provide vital theoretical value for NCA/Si-C power battery system. Chemical-calorimetric combination technology was adopted for detecting the relation between voltage, current, heat flow signal and time during the electrode reaction process. Also the internal heat generation mechanism and temperature distribution rules of NCA/Si-C lithium-ion power batteries under various discharge rates and temperature conditions were explored, and the relevance of electrical/thermal properties and temperature were systematically evaluated. Furtherly, the formation pathways of reversible and irreversible heat were lucubrated for acquiring the interrelation of main thermodynamics parameters(△rHm、△rSm and △rGm）referring to the main and side electrochemical reactions and SOC（State of Charge）during the charge-discharge process. Meanwhile, the influence of the above thermodynamics parameters on SOH（State of Health）were conducted. In addition, the decay mechanism of electrode materials under the interaction of electrochemical and thermal effects was revealed from the microscopic perspective. On this basis, a compound liquid-cooling thermal management modeling coupling with excellent thermal conductive interface materials was constructed. Also the impact rules of flow and heat transfer methods, working medium properties and operating conditions on the heat dissipation efficiency are disclosed.

本项目以提高三元/硅碳锂电池实际装车应用中的热安全性为导向，系统深入研究其电化学-热力学特征参数之间相互关系及复合导热模型传热规律，对助力此体系电池热安全性快速提升，具有重要的理论指导价值。采用电化学-量热方法研究电极反应过程电压、电流、热流与时间关系，探索出不同温度/倍率条件下的电池内部产热机制及温度分布规律，系统评价其电学特性、热学性质及温度的相互关系，进一步探究可逆热及不可逆热生成途径，获得电池充放电过程主副反应的化学热力学状态函数（焓变△rHm、熵变△rSm、吉布斯自由能变△rGm）与SOC（State of Charge）相互关系，研究上述参数对电池SOH（State of Health）的影响规律，从微观角度逆向揭示电极材料在电化学-热效应相互作用下衰退机理。在此基础上，构建液冷板耦合高导热界面材料复合热管理模型，找出流动与传热方式、流体物性、操作条件等对模型传热效率影响规律。

本项目聚焦三元/硅碳锂电池实际装车应用中的热安全性，从“三元/硅碳锂电池的热-电化学行为研究-电池微观热电化学特性与宏观产热规律的相关性研究-模组产热研究-液冷板耦合导热界面材料复合热管理模型的构建及流动传热规律研究”这一研究思路”开展本课题的相关研究。. 对于目前此类化学体系动力锂电池产热特性和电化学性能独立研究存在的问题，尤其是热效应-电化学两者相关性更少涉及，本项目采用电化学-量热方法对三元/硅碳锂电芯在充/放电过程中的热-电特性相关性进行了系统研究，重点分析了过放电滥用对于此类化学体系电芯的基础电化学性能和产热行为的影响规律及机理。结果表明过放电滥用会引起电芯电化学性能衰退和产热加剧，增加了电池发生热失控的风险。宏观性能的衰退进一步引起电芯内部结构及形貌的不可逆损坏，导致导电活性物质与极片严重剥离、活性物质发生团聚。. 在以上研究的基础上，进一步探究可逆热及不可逆热生成途径，获得电池充放电过程主副反应的化学热力学状态函数随着SOC 的变化规律。结果表明在电池总产热里面，欧姆热占50%，极化热和熵热共占50%，并且随着电池状态变化。在此基础上，研究电绝缘型和阻燃型复合相变材料并进行性能表征和应用评价，构建液冷板耦合高导热界面材料复合热管理模型，找出流动与传热方式、流体物性、操作条件等对模型传热效率影响规律。结果表明此复合热管理系统可以实现电池模组内部的最大温差在5℃以内，具有良好的控制温升和均衡温度的能力。相关研究将对于提升高能量密度三元硅碳锂电池的热安全及产业化推广应用具有重要的指导意义和理论支撑。