本文選題：高分子物理　切入點(diǎn)：聚乙烯微孔膜　出處：《中國科學(xué)技術(shù)大學(xué)》2017年博士論文　論文類型：學(xué)位論文

【摘要】：鋰離子電池廣泛應(yīng)用于3C產(chǎn)品,已經(jīng)成為人類不可或缺的消費(fèi)品。延長電池使用壽命、增強(qiáng)充放電穩(wěn)定性,無疑是消費(fèi)者對(duì)3C產(chǎn)品的普遍期待。微孔隔膜作為鋰離子電池非常重要的組成材料,其失效會(huì)導(dǎo)致鋰離子電池正負(fù)電極的直接接觸并引發(fā)短路。由此可見,微孔隔膜對(duì)于鋰離子電池的安全性、壽命以及充放電穩(wěn)定性具有重要的作用。而研究和明確鋰離子電池微孔隔膜制備過程中的基礎(chǔ)物理問題,才能有效地改善其性能。盡管針對(duì)鋰離子電池微孔隔膜的制備已經(jīng)有較多的研究,但是多數(shù)的研究還是基于干法聚丙烯(PP)和濕法聚乙烯(PE)微孔膜的研究,對(duì)干法PE微孔膜的系統(tǒng)研究還比較少,加工過程中存在的很多問題和難點(diǎn)還沒完全認(rèn)識(shí)清楚。本論文為了回答干法PE微孔膜制備過程中涉及的流動(dòng)場誘導(dǎo)結(jié)晶、機(jī)械能和熱效應(yīng)對(duì)微孔成核與生長的作用、高度取向片晶簇?zé)o定形區(qū)的變形模式、片晶簇在應(yīng)變-溫度空間的變形機(jī)理等物理問題,選取高密度聚乙烯(HDPE)為研究對(duì)象,結(jié)合高時(shí)間、空間分辨的同步輻射X射線散射、掃描電鏡(SEM)、透氣性測試等研究手段,從預(yù)制膜的制備到微孔膜后拉伸研究了微孔膜制備過程中的多尺度結(jié)構(gòu)演變,為高性能HDPE微孔膜的研究積累了基礎(chǔ)數(shù)據(jù)和產(chǎn)品開發(fā)思路。本論文的主要結(jié)果和結(jié)論總結(jié)如下:1)通過改變?nèi)垠w擠出-流延過程中口模溫度和流延拉伸比等工藝參數(shù)來改變?nèi)垠w結(jié)晶過程中的流動(dòng)場強(qiáng)度制備了含不同結(jié)構(gòu)的HDPE預(yù)制膜,預(yù)制膜通過一種新型拉伸方法——受限拉伸制備了微孔膜。通過X射線小角散射(SAXS)和X射線廣角散射(WAXS)測得了預(yù)制膜的結(jié)構(gòu)參數(shù)如長周期、片晶側(cè)向尺寸、取向度和纖維晶含量,微孔膜的形貌則通過SEM進(jìn)行表征。本論文發(fā)現(xiàn)纖維晶含量和取向度在預(yù)制膜制備及拉伸成孔過程中是矛盾的。平衡這一對(duì)矛盾的窗口為纖維晶含量為6.4%左右,此時(shí)微孔膜可實(shí)現(xiàn)最大孔隙率和最均勻的微孔結(jié)構(gòu)。本論文還提出了旋轉(zhuǎn)片晶、平行排列的取向片晶、纖維晶對(duì)于微孔的形成扮演的角色的模型,并構(gòu)建了 HDPE預(yù)制膜纖維晶含量-預(yù)制膜微觀結(jié)構(gòu)-成孔能力的關(guān)系。2)采用原位和離線SAXS跟蹤冷拉后的HDPE膜在低溫和升高溫度下兩步應(yīng)力松弛的結(jié)構(gòu)演變,應(yīng)力松弛過程中保持拉伸應(yīng)變恒定。研究發(fā)現(xiàn)冷拉誘導(dǎo)的片晶簇密度漲落在應(yīng)力撤去時(shí)能完全回復(fù),因此將冷拉誘導(dǎo)的密度漲落稱為微孔胚胎。低溫下機(jī)械能釋放使微孔胚胎演變成微孔核存在一段誘導(dǎo)期,并在機(jī)械能繼續(xù)釋放下非均勻生長,最終通過熱拉放大為連通性差的非均勻分布微孔結(jié)構(gòu)。而在升高溫度下的機(jī)械能釋放,微孔胚胎能夠轉(zhuǎn)化為均勻分布的微孔和纖維晶,可作為熱拉過程中連通孔的擴(kuò)展位點(diǎn),進(jìn)而通過熱拉放大的微孔膜不僅微孔分布和孔徑均勻而且透氣性好。本工作暗示低溫下機(jī)械能釋放導(dǎo)致的微孔成核實(shí)際上不利于微孔均勻生長,冷拉后通過熱效應(yīng)固定微孔結(jié)構(gòu)是制備窄孔徑分布和高透氣性的微孔膜的有利條件。3)采用時(shí)間分辨原位SAXS跟蹤跨越兩個(gè)數(shù)量級(jí)的拉伸速率下含高度取向片晶簇結(jié)構(gòu)的HDPE預(yù)制膜的結(jié)構(gòu)演變,發(fā)現(xiàn)不同速率對(duì)應(yīng)于不同的變形模式,與無定形區(qū)分子鏈的松弛響應(yīng)有關(guān)。低速率下,松弛時(shí)間短的結(jié)構(gòu),如纏結(jié)密度小、末端鏈等區(qū)域容易被拉開,拉開之后變形容易應(yīng)力集中,進(jìn)一步擴(kuò)展成非均勻形變,造成二階峰在整個(gè)形變過程中都較弱。高拉伸速率下,各級(jí)結(jié)構(gòu)對(duì)應(yīng)的松弛時(shí)間和拉伸速率都不匹配,不容易發(fā)生松弛,而容易使無定形區(qū)發(fā)生均勻形變,導(dǎo)致二階峰增強(qiáng),非均勻信號(hào)(Icav)減弱。本工作研究的區(qū)間Ⅰ(0.04 mm/s-0.4 mm/s)在拉伸過程中主要發(fā)生非均勻形變,產(chǎn)生空洞化;區(qū)間Ⅱ(0.4mm/s-2.4mm/s)是非均勻形變和均勻形變共存,且發(fā)展能力相當(dāng);區(qū)間Ⅲ(2.4 mm/s-4mm/s)主要發(fā)生拉伸誘導(dǎo)片晶簇分離引起密度漲落的均勻形變。本論文有望為無定形區(qū)松弛時(shí)間譜的分析提供新思路。4)選取含高度取向片晶簇的預(yù)制膜,通過改變冷拉參數(shù)制備了 HDPE微孔膜。制備過程中片晶簇的演化和微孔的形成用原位和離線SAXS、WAXS以及SEM進(jìn)行跟蹤。研究發(fā)現(xiàn)在25℃下冷拉,當(dāng)應(yīng)變低于60%時(shí),冷拉應(yīng)變主要影響片晶簇分離程度,更高應(yīng)變下則主要發(fā)生晶體滑移。冷拉溫度低于60℃能夠促進(jìn)片晶簇的分離,而在冷拉溫度高于60℃時(shí)片晶中的分子鏈容易被拉出形成微纖。此外,本論文揭示了最后微孔膜的透氣性和片晶的分離程度呈線性關(guān)系。
[Abstract]:Lithium ion batteries are widely used in 3C products, has become an indispensable consumer goods. Prolonging the service life of the battery charge and discharge, enhance the stability, is undoubtedly the common expectation of consumers 3C products. As an important component of lithium ion battery materials, microporous membrane, its failure will lead to direct contact with the negative electrode of lithium ion batteries and cause short circuit thus, safety of microporous membrane for lithium ion batteries, which plays an important role in life and discharge stability. And the research and preparation of microporous membrane for lithium ion batteries prepared clear basic material in the process of the problem and can effectively improve the performance of lithium ion battery. Although the microporous membrane preparation has been researched however, most research is based on the dry and wet polyethylene polypropylene (PP) (PE) of microporous membrane, system of dry PE microporous membrane research is still relatively Little, many problems and difficulties in the process is not fully understood. In this paper, in order to answer the preparation process of dry PE microporous membrane system involved in flow induced crystallization, mechanical and thermal effects on the pore nucleation and growth effect of deformation mode of highly oriented lamellar clusters of amorphous region, lamellae in the cluster temperature space strain deformation mechanism and other physical problems, selection of high density polyethylene (HDPE) as the research object, combined with the high time, synchrotron radiation X ray scattering spatial resolution, scanning electron microscopy (SEM), permeability test and other research methods, from the pre prepared membrane preparation to microporous membrane was studied after tensile microporous membrane system evolution of multiscale structure in the preparation process, to accumulate basic data and the product development research for high performance HDPE microporous membrane. The main results and conclusions are summarized as follows: 1) by changing the melt extrusion die flow extension process The temperature and the casting process parameters to change the ratio of melt crystallization in the process of flow field strength of prepared HDPE films containing different prefabricated structures, prefabricated film with a new drawing method of constraint were prepared by X microporous membrane. Small angle X-ray scattering (SAXS) and wide angle X ray scattering (WAXS) the structure parameters such as long cycle measured pre film, crystal lateral dimensions, orientation and content of Xian Weijing, morphology of microporous membranes were characterized by SEM. It is found in this paper are contradictory Xian Weijing content and degree of orientation in preformed membrane preparation and micro pore forming process. The balance of the contradiction between the window for Xian Weijing the content is about 6.4%, the microporous membrane can achieve maximum porosity and the uniform pore structure. This paper also puts forward rotation of lamellae, lamellae oriented parallel to the formation of microporous, Xian Weijing plays the role of the model, and the Construction of HDPE prefabricated fibrous membrane - membrane micro - structure content of prefabricated hole forming ability.2) HDPE membrane by in situ and off-line SAXS tracking after cold drawing should structure evolution of stress relaxation at low temperature and high temperature under the two step, should maintain a constant tensile strain relaxation process. The study found that cold induced crystal clusters the density fluctuation in the stress response can be completely removed, so the density fluctuation induced by cold called microporous embryos. Low temperature mechanical energy release of the porous embryo evolved into microporous nucleus there is a section of the induction period, and the mechanical energy to continue to release under non uniform growth, through thermal amplification for the poor connectivity of non uniform distribution the microporous structure at elevated temperatures. And the release of mechanical energy into uniform micropore and microporous fibrous embryos can be, can be used as the extension locus in the process of hot hole, then through thermal amplification Microporous membrane not only microporous distribution and uniform pore size and good permeability. This work suggests that low temperature mechanical energy release caused by microvoid nucleation in fact is not conducive to the uniform microporous growth, after the cold drawing of the thermal effect of fixed pore structure is prepared with narrow pore distribution and favorable conditions of high permeability microporous membrane of.3) by the time evolution of structure resolution in situ SAXS tracking across HDPE prefabricated membranes containing highly oriented lamellae cluster structure is two orders of magnitude of strain rate under the different rate corresponding to different modes of deformation, and no relaxation of the amorphous region of molecular chain response. Low rate, structural relaxation time is short, such as entanglement density is small, the terminal chain etc. area easily opened, opened after the easy deformation of stress concentration, and further extended into non homogeneous deformation, caused by the two order peak is weak in the whole deformation process. High tensile rate, the structure of the corresponding levels The relaxation time and stretching rate does not match, not prone to relaxation, and easy to make the amorphous region of uniform deformation, resulting in two order peak enhancement, inhomogeneous signal (Icav) decreased. In this work, the interval I (0.04 mm/s-0.4 mm/s) non homogeneous deformation mainly occurred during the stretching process, produce hollowing; section II (0.4mm/s-2.4mm/s) is a non uniform deformation and uniform deformation coexist, and development ability; section III (2.4 mm/s-4mm/s) occurred mainly stretch induced lamellar cluster separation caused by uniform deformation density fluctuation. This thesis is expected to provide new ideas for the analysis of.4 no area of the relaxation time spectrum) from prefabricated membranes containing highly oriented crystal clusters, by changing the parameters of cold drawn HDPE microporous membrane was prepared. The preparation process and the evolution of micro crystal clusters formed by in situ and offline SAXS, WAXS and SEM on track. Now 25 DEG C when drawn, Strain is less than 60%, the main effect of cold drawn strain lamellae cluster separation degree, higher strain is mainly crystal slip. Cold temperature lower than 60 DEG C can promote the separation of crystal clusters, and in the cold temperature higher than 60 DEG C when the molecular chains in crystalline form is easy to pull out micro fiber. In addition, this paper reveals there was a linear relationship between the final microporous membrane permeability and lamellar separation degree.

【學(xué)位授予單位】：中國科學(xué)技術(shù)大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2017
【分類號(hào)】：TM912;TB383.2

【參考文獻(xiàn)】

相關(guān)期刊論文 前6條

1 陳賢德;謝嘉宜;徐睿杰;雷彩紅;;擠出吹塑聚丙烯微孔膜的制備及性能[J];塑料;2016年05期

2 沈鵬;李娟;楊興成;劉晶如;俞強(qiáng);;硬彈性HDPE流延基膜冷拉過程中顯微結(jié)構(gòu)的變化[J];化工學(xué)報(bào);2016年07期

3 向明;蔡燎原;曹亞;亢健;吳桐;;干法雙拉鋰離子電池隔膜的制造與表征[J];高分子學(xué)報(bào);2015年11期

4 徐佳麗;孟令蒲;林元菲;陳曉偉;李薛宇;雷彩紅;王衛(wèi);李良彬;;熔融拉伸法制備聚丙烯微孔膜成孔機(jī)理的原位小角X射線散射研究[J];高分子學(xué)報(bào);2015年04期

5 趙錦成;楊固長;劉效疆;崔益秀;;鋰離子電池隔膜的研究概述[J];材料導(dǎo)報(bào);2012年S2期

6 丁治天;劉正英;劉葭;馮建民;楊偉;楊鳴波;;高分子量級(jí)分含量對(duì)熔體擠出拉伸法制備聚丙烯微孔膜的影響[J];高分子學(xué)報(bào);2012年04期

相關(guān)博士學(xué)位論文 前1條

1 劉棟;流動(dòng)場誘導(dǎo)交聯(lián)聚乙烯結(jié)晶：點(diǎn)核—串晶核轉(zhuǎn)變機(jī)理[D];中國科學(xué)技術(shù)大學(xué);2015年

，

本文編號(hào)：1618646