Effect of PPR on the pore formation behavior and pore performances of β-iPP microporous membrane used for Lithium-ion battery separator

In this article, six different PPR content samples were prepared to study the effect of PPR on the pore formation behavior and pore performances of β nucleated isotactic polypropylene microporous membranes used for lithium-ion battery separator. Different scanning calorimetry (DSC) and the wide angle X-ray diffraction (WXRD) results indicate that the PPR slightly inhibits the formation of β-crystal and significantly reduces the melting point of the sample. Furthermore, the morphological evolution of samples with different PPR contents during biaxial stretching is characterized by tensile testing and SEM. As the PPR content increases, the mechanical performance of the sample increases, but the deformation uniformity of the sample decreases. Especially, the deformation of samples with high PPR content is more inhomogeneous and denser regions are generated during the stretching process, which not only broadens the pore size distribution of the sample but also reduces the connectivity between the micropores. Interestingly, samples with low PPR content (less than 30%) and high PPR content (higher than 30%) have different effects on sample porosity and pore connectivity at elevated temperatures. In other words, the microporous membranes of different PPR components have completely different pore shutdown mechanisms at high temperatures.