高热稳定性锂电池复合隔膜的制备及表征

发布时间：2018-04-02 09:06

  本文选题：锂离子电池　切入点：隔膜　出处：《武汉理工大学》2014年硕士论文

【摘要】：锂离子电池具有能量密度高和循环寿命长等优点，，被大量应用于移动电子设备和动力装置当中，但是频繁发生的安全事故引起了广泛关注。隔膜对锂离子电池的安全性具有非常重要的影响，本文制备了两种高稳定性的复合隔膜。 首先是对聚烯烃隔膜进行表面改性，聚烯烃隔膜是目前使用最广泛的锂电池隔膜，但是聚烯烃隔膜存在热收缩率太高和电解液浸润性不足的问题。本文通过简单的浸渍和萃取步骤，在聚烯烃隔膜上涂覆高孔隙率的乙基纤维素涂层。研究了乙基纤维素涂层对隔膜热收缩率、电解液浸润性、拉伸强度和电化学性能的影响。利用纤维素较高的热稳定性，使涂覆后聚烯烃隔膜的热收缩率明显降低，减少了锂离子电池因隔膜热缩导致内部短路的可能，提高其热安全性。同时因为乙基纤维素涂层带有较多的极性基团和具有互相贯通的孔结构，可以被电解液快速浸润，解决了聚烯烃隔膜因电解液浸润性差而导致的循环性能下降的问题。单层PE隔膜在涂覆后，热闭孔时（132℃）的收缩率从20％降低到9％，最大热收缩率从42％降低到23％，升温测试发现开路电压降为0的温度从130℃推迟到160℃。不仅如此，因为乙基纤维素具有更好的电解液亲合力，涂覆后PP/PE/PP隔膜的电解液浸润性显著提高，使循环后的容量保持率从28%提升至99%。 其次，本文制备了一种高孔隙率的PVDF-HFP/ePTFE复合锂离子电池隔膜。其中，多孔的PVDF-HFP可以吸纳大量的电解液，并且在温度达到其熔点时发生热闭孔而切断电流，防止因温度进一步上升而发生热失控反应。同时以耐高温的ePTFE作为骨架，不但能够提高机械强度，还能够在隔膜热闭孔后保持结构稳定，避免发生熔化短路。该复合隔膜不仅具有良好的离子电导率和电解液浸润性，还可以在升温时保持较低的热收缩率，防止因为热收缩导致正负极接触短路。实验显示，该隔膜在室温下的离子电导率为1.29mS· cm-1，在162℃时的热收缩率为8.8％。隔膜在162℃时发生热闭孔并迅速切断电流，在温度升至329℃之前依然可以保持结构完整。使用该复合隔膜的扣式电池表现出了良好的倍率和循环性能。
[Abstract]:Li-ion batteries are widely used in mobile electronic devices and power devices because of their high energy density and long cycle life. However, frequent safety accidents have aroused widespread concern. Diaphragm has a very important impact on the safety of lithium-ion batteries. In this paper, two kinds of composite membranes with high stability have been prepared. The first is to modify the surface of polyolefin separator, which is the most widely used lithium battery membrane. However, the polyolefin membrane has the problems of too high thermal shrinkage and insufficient electrolyte wettability. The effects of ethylcellulose coating with high porosity on thermal shrinkage, electrolyte wettability, tensile strength and electrochemical properties of polyolefin membranes were studied. The thermal shrinkage rate of the coated polyolefin membrane was obviously reduced, and the possibility of short circuit caused by the thermal shrinkage of the membrane was reduced. Improve its thermal safety. Also because the ethylcellulose coating has more polar groups and interpenetrating pore structures, it can be rapidly infiltrated by the electrolyte, It solves the problem that the cycle performance of polyolefin separator is decreased due to poor electrolyte wettability. The shrinkage rate decreased from 20% to 9%, the maximum thermal shrinkage rate decreased from 42% to 23%, and the temperature at which the open circuit voltage dropped to 0 was delayed from 130 鈩

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