Facile Preparation of a Lithium-Ion Battery Separator with Thermal Shutdown Function Based on Polypropylene/Polyethylene Microsphere Composites

With the continuous development of energy density and charge–discharge rates of lithium-ion batteries in recent years, safety function has become the most concerning issue. In this work, a polypropylene (PP)/polyethylene (PE) composited separator with shutdown function is prepared by a facile dry process with biaxial stretching. Owing to the thermodynamic incompatibility between PP and PE, PE crystallizes initially upon cooling and separates from PP melt, forming ample nanoscale PE microspheres within the PP matrix. The weak interfaces between PE microspheres and PP debond during biaxial stretching to create numerous micropores directly. More importantly, as the temperature rises to 135 °C, PE within the separator melts to block the channels for Li-ion transport; meanwhile, the PP matrix maintains the overall dimensional stability of the separator to prevent the internal short circuiting. Compared with the commercial PP/PE/PP trilayer separator manufacturing technique, this approach has advantages of simple techniques, environmental friendliness, continuous fabrication, and low manufacturing cost, which can offer practical guidance for large-scale low-cost manufacturing of high-performance separators.