干法双拉锂离子电池隔膜的制造与表征

Manufacturing and Characterization of Polypropylene Separators for Lithium Ion Battery via Biaxially Stretching Method

总结了对β-PP铸片晶片分布的均匀性进行快速评价,进而衡量隔膜的孔径分布、厚度分布均匀性的最新研究思路和进展.相关研究通过精确控制结晶温度制备了5组具有相似结晶度、高β晶含量但是不同晶片厚度分布的β-PP流延铸片,并对其β晶片的厚度分布情况进行分析.对其进行拉伸测试,发现了其应力应变曲线出现奇特的二次屈服现象.通过对β-PP在不同拉伸阶段的结构形态进行详细表征,得出二次屈服点是折叠链晶片拉直转化为无定型相的过渡点.同时发现β晶晶片分布越窄,二次屈服出现时的应变值就越大.另一方面,对铸片进行双向拉伸制备隔膜,发现晶片分布越窄的铸片生产的隔膜孔径分布就越窄.退火热处理后的拉伸测试也进一步验证了此规律.因此,可利用室温下的单轴拉伸测试对β-PP流延铸片内部晶片分布宽度,以及其所制备隔膜的孔径分布进行简单而有效地评价.

This manuscript reviews the latest progress to characterize the uniformity of lamellar thickness,the tensile behavior and the uniformity of cavitation during stretching of the casting film, and further to predict the pore size distribution and thickness distribution of the final separator. Five β-PP precursor films, which had similar crystallinity and extremely high contents of β-crystals,but different lamellar thickness distribution,were prepared through crystallizing at different temperatures. In the tensile test,we first discovered a peculiar double yield phenomenon in β-PP under tensile loading. Based on the detailed characterization of morphological evolution during stretching ,we concluded that the second yield point corresponds to the transition point where the lamellae began to transform into amorphous phase. Meanwhile, a narrower β-lamellar thickness distribution would result in a homogeneous deformation, delayed occurrence of second yield point and a more uniform pore size distribution in the porous membrane. In addition, the stress-strain behaviors of β-PP after annealing treatments also verified the trend above. Therefore, the uniaxial tensile testing can be used to evaluate the lamellar thickness distribution of β-PP cast films efficiently.