Hao Wenqian, Bo Xiqiao, Xie Jiamiao, Xu Tingting
The College of Mechatronic Engineering, North University of China, Taiyuan 030051, China.
Underground Target Damage Technology National Defense Key Discipline Laboratory, North University of China, Taiyuan 030051, China.
Polymers (Basel). 2022 Sep 3;14(17):3664. doi: 10.3390/polym14173664.
High tensile strength and toughness play an important role in improving the mechanical performance of separator films, such as resistance to external force, improving service life, etc. In this study, a nanoindentation experiment is performed to investigate the mechanical properties of two types of separators for LIBs based on the grid nanoindentation method. During the indentation experiment, the "sink-in" phenomenon is observed around the indenter when plastic deformation of the specimen occurs. The "sink-in" area of the polyethylene (PE) separator is larger than that of the polypropylene/polyethylene/polypropylene (PP/PE/PP) separator, i.e., the plastic area of the PE separator is larger than that of the PP/PE/PP separator. In order to select a suitable method to evaluate the hardness and elastic modulus of these separators for LIBs, three theoretical methods, including the Oliver-Pharr method, the indentation work method, and the fitting curve method, are used for analysis and comparison in this study. The results obtained by the fitting curve method are more reasonable and accurate, which not only avoids the problem of the large contact area obtained by the Oliver-Pharr method, but also avoids the influence caused by the large fitting data of the displacement-force curve and the inaccuracy of using the maximum displacement obtained by the indentation method. In addition, the obstruction ability of the PP/PE/PP separator to locally resist external load pressed into its surface and to resist micro particles, such as fine metal powder, that can enter the lithium-ion battery during the manufacturing process is greater than that of the PE separator. This research provides guidance for studying the mechanical properties and exploring the estimation method of macromolecular separators for LIBs.
高拉伸强度和韧性在提高隔膜的机械性能方面起着重要作用，例如抵抗外力、延长使用寿命等。在本研究中，基于网格纳米压痕法进行了纳米压痕实验，以研究两种锂离子电池隔膜的机械性能。在压痕实验过程中，当试样发生塑性变形时，在压头周围观察到“压入”现象。聚乙烯（PE）隔膜的“压入”面积大于聚丙烯/聚乙烯/聚丙烯（PP/PE/PP）隔膜，即PE隔膜的塑性区域大于PP/PE/PP隔膜。为了选择一种合适的方法来评估这些锂离子电池隔膜的硬度和弹性模量，本研究使用了三种理论方法，包括奥利弗-法尔法、压痕功法和拟合曲线法进行分析和比较。拟合曲线法得到的结果更合理、准确，既避免了奥利弗-法尔法得到的接触面积过大的问题，又避免了位移-力曲线拟合数据过大以及使用压痕法得到的最大位移不准确所带来的影响。此外，PP/PE/PP隔膜对局部抵抗压入其表面的外部载荷以及抵抗在制造过程中可能进入锂离子电池的微粒（如细金属粉末）的阻挡能力大于PE隔膜。本研究为研究锂离子电池高分子隔膜的机械性能和探索估算方法提供了指导。
