Abstract: An electrochemical cell having a composite alkali ion-conductive electrolyte membrane. Generally, the cell includes a catholyte compartment and an anolyte compartment that are separated by the composite alkali ion-conductive electrolyte membrane. The composite electrolyte membrane includes a layer of alkali ion-conductive material and one or more layers of alkali intercalation compound which is chemically stable upon exposure to a chemically reactive anolyte solution or catholyte solution thereby protecting the layer of alkali ion-conductive material from unwanted chemical reaction. The layer of alkali intercalation compound conducts alkali ions. The cell may operate and protect the alkali ion-conductive material under conditions that would be adverse to the material if the intercalation compound were not present. The composite membrane may include a cation conductor layer having additional capability to protect the composite electrolyte membrane from adverse conditions.