A Novel Cavity-Enhanced Polyethylene/Nanostructured-Alumina Separator with Long Cycle Life and High Rate Capability for Advanced Lithium-Ion Batteries

Traditional polyolefin separators cannot meet the increasing requirements of lithium-ion batteries (LIBs) for the high power density, high energy density, and high safety that the secondary battery market has expanded to electric vehicles. It is still a great challenge to reduce ion-transport resistance, promote thermal stability, and improve the mechanical properties of polymer-based separators. Herein, a novel composite separator with enhanced conductivity, good mechanical strength, and high thermo-dimensional stability is designed and demonstrated for the application of advanced LIBs. The flexible multiarm structure of nanostructured alumina nanoparticles (NPs) greatly promotes the orientation of high density polyethylene (HDPE) during the polymer processing, significantly enhancing the pore cavity during the separator formation process. The porosity, pore size distribution, thermo-dimensional stability, and mechanical strength of the resultant composite separator are significantly improved, leading to long cycle life and high rate capability. The orientation/crystallization development of HDPE by the introduction of alumina NPs has been examined via microstructure analysis. This demonstration not only shows the high impact on the separator manufacturing of LIBs with a high power density and high safety but also creates a new method in controlling the orientation and cavity design of polyolefin materials.