车用锂离子电池组机械应力特性分析及物理建模

Fast performance degradation of lithium-ion battery packages in pure electric vehicles occurs seriously. However, the current battery package design and battery management system can only represent battery performance characteristics based on the measurements of battery voltage, current, and temperature, not do the degradation mechanism of lithium-ion batteries. It is important for us to investigate and study the lithium intercalation diffusion induced stress characteristics and physics modeling of lithium-ion batteries. In this project, the life cycle mechanical stress behavior of battery package is the multi-factor coupling and significant nonlinear to be studied through three aspects. Firstly, through the life cycle test of the relation between mechanical stress and strain, how much the battery stress is influenced will be weighed by factors, and how it changes will be generalized. Secondly, through the visual microscope technology, the battery electrochemical features will be investigated and manifested in the mechanical stress to build the electrochemical, thermal, and mechanical multi-scale and multi-physics coupling cell model. Finally, through the combination of both multi-physics coupling model and lumped parameter surface stress model of the battery cell, a distributed parameter model of mechanical stress of the battery package will be constructed to be applied for the simulation and evaluation of stress transfer and distribution, the results of which will be used to develop the battery package. On the basis of our research foundation, our research team will complete the mechanical stress finding, model simulation, and validation, with numerical computation and life cycle test at environment warehouse. Our research objective is to propose a homogeneous design methodology of mechanical stress to develop vehicle battery packages and produce a mechanical stress model base of battery state estimation.

纯电动汽车锂离子电池组性能衰退快的问题突出。目前的电池组设计方法和电池管理系统以电压、电流和温度三个参数表征电池性能特性，缺乏对电池衰退机理性问题的表征。为此研究电极嵌锂扩散诱发的电池机械应力特性及其建模方法具有重要意义。课题拟从三个层面研究电池寿命循环过程中多耦合因素、严重非线性的车用电池组机械应力。① 基于寿命循环电池机械应力应变的测试，分析电池机械应力的影响因素和变化规律。②运用微观可视化技术，探索单体电池电化学行为的机械应力表征，建立单体电池电化学、热学和机械学多物理场耦合机理模型。③ 集成单体电池面应力集总参数模型和耦合机理模型为电池组机械应力分布参数模型，仿真评估电池组机械应力的传递与分布，用于电池组开发。课题组将通过数值计算和环境仓寿命循环实验等手段，完成锂离子电池组机械应力的规律发现、模型仿真与验证工作，建立电池组机械应力一致性设计方法，奠定电池状态估计的机械应力模型基础。

以纯电动汽车为主的新能源汽车在国内外快速市场化，然而车载锂离子电池组性能衰退快和热失控等问题突出。目前的电池组设计方法和电池管理系统以电压、电流和温度三个参数表征电池性能特性，缺乏对电池衰退机理性问题的全面表征。为此研究电极嵌锂扩散诱发的电池机械应力特性和多物理场建模方法具有重要意义。项目以方形三元材料锂离子电池为主研究其充放电过程中的机械、电气和热学耦合行为表征方法，主要研究内容包括：① 设计和开发了反应锂离子电池机械应力应变的面压力和厚度测量装置，分析电池机械应力的影响因素和变化规律。② 设计和开发了锂离子电池热物性参数测量装置，提出了可靠低成本的电池比热容和导热系数测量方法。③ 研究了集总粒子电化学模型，提出了适应倍率和温度变化的模型参数化方法。④ 采用集总粒子电化学模型和三维热模型，提出了基于均匀热源和表面温度反馈的热电耦合模型建模方法。⑤ 研究了基于等效电路的电池二维展向电流密度的分布式热源模型，与三维热模型耦合，提出了基于分布式热源的热电耦合模型建模方法。开发的装置成功测量了软包电池机械压力、方形电池厚度变化量、电极材料导热系数和电池比热容，结果表明所提出的热物性参数测量方法可靠、低成本。软包电池的机械压力受到倍率、容量变化、充电截止电压和静置时间的影响，而方形电池的厚度变化受到温度和容量变化影响，与温度出现正相关性。所提出的集总粒子电化学模型参数化方法，提高了模型的倍率和温度适应性，以恒流充放电实验验证表明，在30%-90%SOC的模型电压误差介于±35mV。所构建的三个热电耦合模型具有相同的电池表面温度变化趋势，表面温度误差介于±1.1℃。其中，基于卷绕体温度反馈的分布式热源热电耦合模型能够用来分析电池内部的电流密度、电极电势和温度场分布，计算量最大。基于表面温度反馈的均匀热源热电耦合模型仿真时间最少，可用来快速预测电池表面温度，为电池组一致性设计奠定了热电耦合分析基础。