Lithium metal batteries (LMBs) are a key product for sustainable and efficient electric transport. Long-life and safe LMBs require the development of solid or semisolid (e.g., gel polymer) electrolytes capable of blocking lithium dendrites. In this context, Janus double-faced membranes (JMs) offer interesting perspectives, as they allow for modulating the properties of each side according to specific requests. In this paper, we report on facile fabrication via the solvent casting of JMs based on poly(vinylidene fluoride hexafluoropropylene) (PVDF-HFP). Here, an electronically insulating layer containing Al2O3 is in contact with the anode, whereas a mixed ionically–electronically conducting layer containing Al2O3, carbon nanotubes, and Super P carbon black is in contact with the cathode. We also investigate the role of the JM thickness and show that a 40 μm membrane allows for ~45% of the specific nominal capacity at 2C with Coulombic efficiency of ~100%. The proposed JMs are very promising for LMBs.