微孔膜机械性能与热稳定性能的数值分析
发布时间：2019-05-21 19:47
【摘要】：带微纳孔洞结构的聚烯烃薄膜不仅具有良好的机械性能,还有较好的离子穿透能力,其中聚乙烯、聚丙烯微孔膜具有较高孔隙率、较低的电阻、较好的力学性能、较稳定的化学性能、良好的弹性,因此在锂离子电池隔膜领域得到广泛应用。隔膜在锂离子电池中起到的作用是既要分隔正负极又要保证锂离子的正常通过,隔膜的性能将直接影响电池的容量、安全与循环性能。当前大多数研究者都是从实验角度来观察隔膜孔洞形成情况,检测薄膜的力学性能,很少用计算机模拟来研究薄膜微孔结构的形成机制。本文采用计算机对聚乙烯薄膜进行分子动力学模拟,从微观尺度上探讨微孔薄膜的孔洞形成机制、结构特点、机械性能、热稳定性能、锂离子穿透率,同时研究微观结构与宏观特性之间的相互关系。主要研究内容分为以下三个部分：首先对纯聚乙烯薄膜进行分析,采用自回避随机游走的方法生成粒子的空间坐标位置,建立简化粗粒化模型,对该粗粒化模型进行熔融、降温结晶,得到更接近真实状态下的半晶态聚乙烯材料,用半结晶薄膜模型进行拉伸,研究此薄膜的成孔机制与力学性能。结果表明,纯聚乙烯薄膜具有良好的力学性能与成孔性能,在微观尺度上解释了薄膜孔洞生成的演变过程。然后是对含有2.8%纳米增强粒子二氧化硅聚乙烯薄膜的机械性能与热稳定能的研究。对SiO2/聚乙烯薄膜进行熔融、降温结晶,并对复合材料的力学性能与热稳定性能模拟分析。研究发现,2.8%SiO2纳米粒子的加入使聚乙烯的屈服强度与弹性模量分别提高了26.6%与19.9%,熔点提高了11℃。最后分析了聚乙烯薄膜孔洞结构对锂离子穿透力的影响。通过对比圆形孔洞与狭长型孔洞的锂离子穿透率,发现在相同孔隙率8.2%及相同孔洞个数下,椭圆形孔洞的锂离子穿透率48.3%大于圆形孔洞的锂离子穿透率39.5%,而且孔隙率越大锂离子的穿透率越大。
[Abstract]:The polyolefine films with microporous structure not only have good mechanical properties, but also have good ion penetration ability. Polyethylene and polypropylene microporous films have higher porosity, lower resistance and better mechanical properties. Because of its stable chemical properties and good elasticity, it has been widely used in the field of lithium ion battery diaphragm. The function of diaphragm in lithium ion battery is not only to separate positive and negative electrodes, but also to ensure the normal passage of lithium ion. The performance of diaphragm will directly affect the capacity, safety and cycle performance of lithium ion batteries. At present, most researchers observe the formation of diaphragm pores from the experimental point of view, detect the mechanical properties of the films, and rarely use computer simulation to study the formation mechanism of the micropores of the films. In this paper, the molecular dynamics simulation of polyethylene film is carried out by computer, and the pore formation mechanism, structural characteristics, mechanical properties, thermal stability and lithium ion penetration rate of microporous film are discussed from the micro scale. At the same time, the relationship between microstructure and macro characteristics is studied. The main research contents are divided into the following three parts: firstly, the pure polyethylene film is analyzed, the spatial coordinate position of particles is generated by self-avoiding random walk, the simplified coarse granulation model is established, and the coarse granulation model is melted. The semi-crystalline polyethylene material which is more close to the real state was obtained by cooling crystallization. The pore formation mechanism and mechanical properties of the film were studied by using the semi-crystalline film model. The results show that the pure polyethylene film has good mechanical properties and pore forming properties, and the evolution process of pore formation in the film is explained on the microscopic scale. Then the mechanical properties and thermal stability energy of silica polyethylene films containing 2.8% nano-reinforced particles were studied. The melting, cooling and crystallization of SiO2/ polyethylene film were carried out, and the mechanical properties and thermal stability of the composites were simulated and analyzed. It is found that the yield strength and elastic modulus of polyethylene are increased by 26.6% and 19.9%, and the melting point is increased by 11 鈩，
本文编号：2482341
[Abstract]:The polyolefine films with microporous structure not only have good mechanical properties, but also have good ion penetration ability. Polyethylene and polypropylene microporous films have higher porosity, lower resistance and better mechanical properties. Because of its stable chemical properties and good elasticity, it has been widely used in the field of lithium ion battery diaphragm. The function of diaphragm in lithium ion battery is not only to separate positive and negative electrodes, but also to ensure the normal passage of lithium ion. The performance of diaphragm will directly affect the capacity, safety and cycle performance of lithium ion batteries. At present, most researchers observe the formation of diaphragm pores from the experimental point of view, detect the mechanical properties of the films, and rarely use computer simulation to study the formation mechanism of the micropores of the films. In this paper, the molecular dynamics simulation of polyethylene film is carried out by computer, and the pore formation mechanism, structural characteristics, mechanical properties, thermal stability and lithium ion penetration rate of microporous film are discussed from the micro scale. At the same time, the relationship between microstructure and macro characteristics is studied. The main research contents are divided into the following three parts: firstly, the pure polyethylene film is analyzed, the spatial coordinate position of particles is generated by self-avoiding random walk, the simplified coarse granulation model is established, and the coarse granulation model is melted. The semi-crystalline polyethylene material which is more close to the real state was obtained by cooling crystallization. The pore formation mechanism and mechanical properties of the film were studied by using the semi-crystalline film model. The results show that the pure polyethylene film has good mechanical properties and pore forming properties, and the evolution process of pore formation in the film is explained on the microscopic scale. Then the mechanical properties and thermal stability energy of silica polyethylene films containing 2.8% nano-reinforced particles were studied. The melting, cooling and crystallization of SiO2/ polyethylene film were carried out, and the mechanical properties and thermal stability of the composites were simulated and analyzed. It is found that the yield strength and elastic modulus of polyethylene are increased by 26.6% and 19.9%, and the melting point is increased by 11 鈩，
本文编号：2482341
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