Disclosed are ionically conductive membranes for protection of active metal anodes and methods for their fabrication. The membranes may be incorporated in active metal negative electrode (anode) structures and battery cells. In accordance with the invention, the membrane has the desired properties of high overall ionic conductivity and chemical stability towards the anode, the cathode and ambient conditions encountered in battery manufacturing. The membrane is capable of protecting an active metal anode from deleterious reaction with other battery components or ambient conditions while providing a high level of ionic conductivity to facilitate manufacture and/or enhance performance of a battery cell in which the membrane is incorporated.