【摘要】：帶微納孔洞結(jié)構(gòu)的聚烯烴薄膜不僅具有良好的機(jī)械性能,還有較好的離子穿透能力,其中聚乙烯、聚丙烯微孔膜具有較高孔隙率、較低的電阻、較好的力學(xué)性能、較穩(wěn)定的化學(xué)性能、良好的彈性,因此在鋰離子電池隔膜領(lǐng)域得到廣泛應(yīng)用。隔膜在鋰離子電池中起到的作用是既要分隔正負(fù)極又要保證鋰離子的正常通過,隔膜的性能將直接影響電池的容量、安全與循環(huán)性能。當(dāng)前大多數(shù)研究者都是從實(shí)驗(yàn)角度來觀察隔膜孔洞形成情況,檢測薄膜的力學(xué)性能,很少用計(jì)算機(jī)模擬來研究薄膜微孔結(jié)構(gòu)的形成機(jī)制。本文采用計(jì)算機(jī)對聚乙烯薄膜進(jìn)行分子動(dòng)力學(xué)模擬,從微觀尺度上探討微孔薄膜的孔洞形成機(jī)制、結(jié)構(gòu)特點(diǎn)、機(jī)械性能、熱穩(wěn)定性能、鋰離子穿透率,同時(shí)研究微觀結(jié)構(gòu)與宏觀特性之間的相互關(guān)系。主要研究內(nèi)容分為以下三個(gè)部分：首先對純聚乙烯薄膜進(jìn)行分析,采用自回避隨機(jī)游走的方法生成粒子的空間坐標(biāo)位置,建立簡化粗�；Ｐ�,對該粗�；Ｐ瓦M(jìn)行熔融、降溫結(jié)晶,得到更接近真實(shí)狀態(tài)下的半晶態(tài)聚乙烯材料,用半結(jié)晶薄膜模型進(jìn)行拉伸,研究此薄膜的成孔機(jī)制與力學(xué)性能。結(jié)果表明,純聚乙烯薄膜具有良好的力學(xué)性能與成孔性能,在微觀尺度上解釋了薄膜孔洞生成的演變過程。然后是對含有2.8%納米增強(qiáng)粒子二氧化硅聚乙烯薄膜的機(jī)械性能與熱穩(wěn)定能的研究。對SiO2/聚乙烯薄膜進(jìn)行熔融、降溫結(jié)晶,并對復(fù)合材料的力學(xué)性能與熱穩(wěn)定性能模擬分析。研究發(fā)現(xiàn),2.8%SiO2納米粒子的加入使聚乙烯的屈服強(qiáng)度與彈性模量分別提高了26.6%與19.9%,熔點(diǎn)提高了11℃。最后分析了聚乙烯薄膜孔洞結(jié)構(gòu)對鋰離子穿透力的影響。通過對比圓形孔洞與狹長型孔洞的鋰離子穿透率,發(fā)現(xiàn)在相同孔隙率8.2%及相同孔洞個(gè)數(shù)下,橢圓形孔洞的鋰離子穿透率48.3%大于圓形孔洞的鋰離子穿透率39.5%,而且孔隙率越大鋰離子的穿透率越大。
[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，

本文編號：2482341