“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.