There is disclosed a polycrystalline lithium-ion conductive membrane for a lithium-air battery that comprises at least one surface, a polycrystalline lithium-ion conductive material comprising grain boundaries, and at least one modifying phase, wherein (a) the at least one modifying phase is incorporated into the grain boundaries to form a modified polycrystalline lithium-ion conductive material comprising modified grain boundaries, (b) the at least one modifying phase is incorporated into the at least one surface to form a modified surface, or both (a) and (b). Various lithium based batteries, including lithium ion, lithium-air, and lithium-water batteries are disclosed, as well as methods for modifying the polycrystalline lithium-ion conductive membrane to allow it to be used in such battery applications.