“Polymer-in-Ceramic” Membrane for Thermally Safe Separator Applications

In this work, a facile casting method was utilized to prepare “polymer-in-ceramic” microporous membranes for thermally safe battery separator applications; that is, a series of composite membranes composed of silicon dioxide (SiO₂) as a matrix and polyvinylidene fluoride (PVDF) as a binder were prepared. The effects of different SiO₂ contents on various physical properties of membranes such as the porosity, electrolyte absorption rate, electrochemical stability, and especially thermal stability of the SiO₂/PVDF composite membranes were systematically studied. Compared with a commercial polypropylene separator, the SiO₂/PVDF membrane has a higher porosity (66.0%), electrolyte absorption (239%), and ion conductivity (1.0 mS·cm^–1) and superior thermal stability (only 2.1% shrinkage at 200 °C for 2 h) and flame retardancy. When the content of SiO₂ in the membrane reached 60% (i.e., PS6), LiFePO₄/PS6/Li half-cells exhibited excellent cycle stability (138.2 mA h·g^–1 discharging capacity after 100 cycles at 1C) and Coulombic efficiency (99.1%). The above advantages coupled with the potential for rapid and large-scale production reveal that the “polymer-in-ceramic” SiO₂/PVDF membrane has prospective separator applications in secondary lithium-ion batteries.