A method for producing a waterproof and ion-conducting flexible membrane intended for protecting a metal electrode. It comprises a synthesis by electrically assisted extrusion of compact fibers forming an ion-conducting fiber array comprising a first material. The fiber array defines a first surface and a second surface opposite the first surface. Subsequently, the fiber array is impregnated with a polymer of a second material, to form a metal electrode protection membrane. The fiber array forms paths for conducting ions between the first surface and the second surface and through the second material. The first surface is intended to be in contact with the metal electrode.