NOVELTY - The assembly (C) has a porous membrane (A) provided with inorganic, electrically insulating and non-alkali-ion conducting material including through pores that are extended from a major surface of the porous membrane to an opposing major surface. An alkali-ion conducting film (B) is placed on the major surface of the porous membrane. The through pores of the porous membrane are sealed by the alkali-ion conducting film. The alkali-ion conducting film comprises inorganic material of predetermined equation. The porous membrane includes average thickness in range from 5 to 500 micrometer.    USE - Glass fiber alkali-ion conducting separator assembly for use in a rechargeable electrochemical cell e.g. lithium-sulfur cell and alkali metal-oxygen cell, of an alkali metal ion battery e.g. water-based secondary battery such as rechargeable alkali metal ion battery e.g. capacitor, accumulator, lithium battery, lithium ion battery, lithium-sulfur battery, alkali metal-oxygen battery, alkaline earth metal battery and air battery or sodium air battery, in a device (all claimed) e.g. mobile device such as vehicle e.g. automobile, bicycle, aircraft, and water vehicle such as boat or ship. Can also be used for a computer, laptop and a telephone for drills, battery-driven screwdrivers and battery-driven tackers.    ADVANTAGE - The assembly provides an inexpensive separator for the long-lived electrochemical cell e.g. lithium-sulfur cell, so that the assembly displays sufficient ion conductivity, high thermal stability and better mechanical properties. The assembly provides prolonged run time before recharging and smaller loss of capacity in course of prolonged run time.    DETAILED DESCRIPTION - The assembly is provided for a rechargeable electrochemical cell that includes a cathode made of electroactive chalcogen-containing material. INDEPENDENT CLAIMS are also included for the following:    (1) a process for producing an alkali-ion conducting separator assembly    (2) a rechargeable electrochemical cell.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross-sectional view of an alkali-ion conducting separator assembly.    Porous membrane (A)    Alkali-ion conducting film (B)    Glass fiber alkali-ion conducting separator assembly (C)    Anode (D)    Cathode (E)