Polypropylene/polyethylene multilayer separators with enhanced thermal stability for lithium-ion battery via multilayer coextrusion

Abstract

A facile and continuous method to prepare porous polypropylene (PP)/polyethylene (PE) multilayer membranes as separators for lithium-ion batteries via multilayer coextrusion and CaCO3 template method is proposed. Scanning electron microscopy (SEM) images indicate that the membrane exhibits abundant and well-connected sub-micron porous structure. Besides, the physical and electrochemical properties of the membranes, such as thickness, porosity, electrolyte uptake, ionic conductivity, electrochemical stability, thermal stability, and battery performance, are characterized and compared with the commercial separators with trilayer construction of PP and PE (e.g., Celgard® 2325). The results indicate that the multilayer PP/PE separators exhibit higher porosity as well as higher electrolyte uptake and retention than Celgard® 2325, which will definitely increase the ionic conductivity, and consequently improve the battery performances. More importantly, the PP/PE multilayer separators not only show effective thermal shutdown function, but also shows significant advantages of high thermal stability up to 160 °C. The thermal shutdown function of PP/PE multilayer membranes can be adjusted widely in the temperature range from 127 °C to 165 °C, which is wider than that of the commercial separators. The above results combined with the convenient and cost-effective preparation process makes porous PP/PE multilayer membranes a promising alternative to the commercialized trilayer lithium-ion battery separators.