锂离子二次电池无机有机复合隔膜的改性研究

发布时间：2018-03-02 21:20

  本文选题：锂离子二次电池　切入点：隔膜　出处：《南京大学》2014年硕士论文　论文类型：学位论文

【摘要】：当今世界,能源问题和环境问题已经成为人类发展所必须面临的重要问题。随着传统一次能源的不断消耗,可再生清洁能源的开发和利用显得十分重要。由于锂离子二次电池具有能量密度大、工作电压高、无记忆效应、环境友好、自放电率低、循环性能好等优点,锂离子二次电池正成为目前研究热点之一。组成锂离子二次电池的关键材料有正极、负极、隔膜和电解液四种材料,本文以隔膜材料作为研究对象。传统的隔膜制备方法主要有干法湿法两种,干法制得的孔径多为狭长孔,且孔径和孔隙率难以控制,孔径不均匀,对锂离子二次电池一致性无明显帮助；湿法包含相分离过程,需要用到溶剂,对环境污染严重。隔膜作为锂离子二次电池的重要组成部分,在锂离子二次电池中发挥着重要的作用。商业的聚烯烃隔膜虽然能满足大部分锂离子二次电池的使用,但是其材料本身特有的性质导致其亲液性差、热稳定性能差等缺点制约了它在锂离子二次电池特别是电动汽车领域的发展。本文发展了一种新型的制膜方法,通过管道受限湿法腐蚀制备了SiO2尖针阵列模板,然后在聚烯烃熔融温度下对其进行热压,制得了均匀的圆形孔洞。研究了不同热压压力对孔洞的影响,发现孔径大小同热压压力呈正比关系。本文分别采用原子层沉积法和涂布法在商业聚丙烯膜表面涂覆了氧化铝无机涂层和聚偏氟乙烯-六氟丙烯有机涂层,有效的改善了隔膜的亲液性和热稳定性能,从而提高了锂离子二次电池的安全性。利用原子层沉积技术制备了氧化铝无机涂层和聚丙烯的复合隔膜,分别研究了不同涂层厚度、单双面涂层对隔膜性能的影响。研究得到双面涂层在各个方面的性能都优于单面涂层。随着涂层厚度的增加,隔膜的热稳定性能和机械性能、亲液性、保液性均有所提高,组装而成的电池相比原始隔膜表现出了更优异的倍率性能和循环性能。研究表明10nm厚度的双面氧化铝涂层对隔膜的性能提升最大,吸液率、保液率均有一倍以上的提高,在160℃环境下,复合隔膜没有任何热收缩,电池在0.1 C倍率下充放电,其放电比容量达到了136.68 mAh/g和137.71 mAh/g,1C、2C倍率快速充放电下,其比容量分别为114.48 mAh/g、 95.90 mAh/g和119.77 mAh/g、107.56 mAh/g。在0.5C和1C分别进行50次充放电后,容量保持率高达96.05%和96.92%。采用倒相法制备了聚偏氟乙烯-六氟丙烯／聚丙烯有机涂层复合隔膜,研究了聚合物本体不同质量分数对其孔洞结构的影响,不同铸膜液配比对孔洞的影响以及不同凝固浴对膜形貌的影响。选取了几种结构优异的复合隔膜对其进行吸液率、保液率、热收缩性能以及电化学性能的测试,复合隔膜表现出了更加优异的性能。
[Abstract]:In today's world, energy and environmental problems have become an important issue for human development. With the continuous consumption of traditional primary energy, The development and utilization of renewable clean energy is very important. Because of the advantages of high energy density, high working voltage, no memory effect, friendly environment, low self-discharge rate and good cycling performance, lithium ion secondary battery has many advantages, such as high energy density, high working voltage, no memory effect, etc. Lithium ion secondary battery is becoming one of the research hotspots at present. The key materials of lithium ion secondary battery are positive electrode, negative electrode, diaphragm and electrolyte. In this paper, the membrane material is taken as the research object. The traditional preparation methods of diaphragm are mainly dry and wet process. The pore size obtained by dry method is mostly long and narrow, and the pore size and porosity are difficult to control, and the pore size is not uniform. It has no obvious help to the consistency of lithium ion secondary battery; the wet process includes phase separation process, which requires solvent, which pollutes the environment seriously. Diaphragm is an important part of lithium ion secondary battery. Although commercial polyolefin separators can satisfy most of the use of lithium ion secondary batteries, the unique properties of the materials lead to poor hydrophilicity. The development of lithium ion secondary battery, especially electric vehicle, is restricted by its poor thermal stability. In this paper, a new film making method is developed, and the SiO2 tip needle array template is prepared by pipe limited wet etching. Then the polyolefin was hot-pressed at the melting temperature, and a uniform circular cavity was prepared. The effect of different hot pressing pressure on the pore was studied. It is found that the pore size is proportional to the hot pressing pressure. In this paper, alumina inorganic coating and polyvinylidene fluoride hexafluoropropylene organic coating were coated on commercial polypropylene film by atomic layer deposition and coating method, respectively. The liquid lipophilic and thermal stability of the membrane was improved effectively, and the safety of lithium ion secondary battery was improved. The composite film of alumina inorganic coating and polypropylene was prepared by atomic layer deposition, and the thickness of different coating was studied. The effect of single and double coating on the performance of diaphragm. The results show that the properties of double-sided coating are better than that of single-sided coating in every aspect. With the increase of coating thickness, the thermal stability, mechanical properties, hydrophilicity and liquid-preserving properties of the film are improved. Compared with the original membrane, the assembled battery has better performance of rate and cycle. The results show that the double-sided alumina coating with a thickness of 10 nm can improve the performance of the membrane by more than twice as much as that of the original membrane, and the absorbency and retention rate of the membrane can be increased by more than one time. At 160 鈩，

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