基于多层次聚集态结构演变的微孔薄膜流延拉伸成形机理与工艺调控研究

Microporous membranes is the key components of energy storage battery and power battery. Its properties directly influence the interface structure, cycling efficiency and security of the battery. However, the independence for key technology of microporous membranes manufacturing is currently difficult to be realized for the lack of theoretical basis for controlling of structure and performance. The technical barriers in high-performance microporous membranes manufacturing still can’t be broken. In the research, a method based on hierarchical aggregation structure evolution is proposed for the investigation of scientific problems in controlling of structure and performance in microporous membranes casting-stretching process. The forming of oriented lamellar structure, the transformation of crystal structure and hard elastic property in recrystallization process, the deformation behavior and microporous forming mechanism will be systematically studied based on rheology theory, condensed matter theory, crystallographic method and plastic mechanics theory. A multiscale theoretical model for the key transformation of aggregation structure will be established. Quantitative analysis of the forming and transformation process of oriented lamellar structure and microporous with effects of external field can be realized through combining molecular dynamics, non-equilibrium thermodynamics and micromechanics method. The combination optimization method based on controlling of structure and property in microporous membranes casting-stretching process will be proposed to provide technical support for practical processing control. The research is expected to make breakthrough both in the key technology of microporous membranes manufacturing and in the key fundamental problem of aggregation structure evolution. The research findings can be of important theoretical significance and also has a good prospect in engineering application.

微孔薄膜是储能电池和动力电池阻隔用关键内层组件，其性能直接影响电池界面结构、循环效率和安全性。因缺乏微孔薄膜结构性能调控理论基础，仍难以实现其关键技术自主化，无法突破高性能微孔薄膜制造技术壁垒。本项目针对微孔薄膜流延拉伸成形性能调控科学问题，提出一种基于多层次聚集态结构演变的研究方法，将高聚物流变学、凝聚态理论、晶体学方法和塑性力学理论相结合，研究微孔薄膜流延过程取向片晶结构形成、退火过程晶体结构与硬弹性能转变、拉伸过程变形力学行为与微孔形成机制关键问题，构建其聚集态结构关键物理转变过程的多尺度理论模型，通过分子动力学、非平衡热力学和微力学方法的结合，实现对复杂外场作用下取向片晶和孔隙结构形成与演化过程的量化分析，提出以结构性能为调控指标的多工艺因素组合优化方法，为实际工艺调控提供支撑。项目拟在微孔薄膜制造关键技术和聚集态结构演变关键基础问题两方面取得突破，具有重要理论意义和工程应用前景。

本项目基于流变学、凝聚态理论、晶体学和塑性力学理论对微孔薄膜流延拉伸聚集态结构演变及其性能调控关键问题开展了系统研究。采用挤出流延工艺制备α-iPP基体薄膜，通过弹性回复测试和二维广角X射线衍射分析，研究了挤出温度和流延比等对薄膜结晶取向和硬弹性的影响，分析了退火处理对晶区结构的影响机制，通过研究冷热拉伸行为并结合孔隙结构分析，探讨了微缺陷形成及其与架桥结构和片晶分离过程的关联，研究了β晶型成核剂对结晶行为的影响，分析比较了α-iPP和β-iPP薄膜拉伸行为，分析了β-iPP薄膜晶型转变和退火不稳定相形成与孔隙结构的关联；建立了挤出过程三维非等温有限元数值模型与算法，研究了模具温度和挤出速度等对熔体流速分布均匀性的影响，将厚度作为求解变量解决厚度方向网格划分问题，采用有限元方法对流延成形速度场、厚度场和自由边界进行数值求解，系统分析了各工艺因素对颈缩和哑铃边等成形缺陷的影响机理，建立了流延过程熔体、流延辊与冷却水换热过程的数值模型并进行了耦合数值求解，分析了冷却水温、流速和流延辊转速等对薄膜温度分布均匀性的影响；采用粗粒化映射和玻尔兹曼转换，获得了高聚物粗粒化模型与力场参数，实现了纳观到微观尺度的过渡，通过几何方法从粗粒化模型中提取原始路径，获得了均方末端距、原始路径长度、管直径和缠结数等关键参数，并基于仿射变形粘弹本构方程预测了粘弹性能参数，实现了微观到宏观尺度的过渡；采用Taguchi法对流延工艺参数进行优化，分析了熔体牵伸比、气隙、挤出温度和流延辊温度等对硬弹性能的影响机制，获得了最优工艺参数组合，研究了应力场中高聚物熔体取向片晶结构形成及其与薄膜性能的关联，分析了片晶分离机理及其对孔隙结构与分布的影响，建立了以退火温度和时间为变量，以弹性回复率为目标的退火过程二阶响应面模型，确定了最优退火条件，分析了退火二次晶体形成及其对薄膜拉伸行为的影响，研究了冷热拉伸条件对片晶分离、架桥结构形成和片晶形变行为的影响机理。