NOVELTY - An electrochemical device comprises a first electrode comprising a lithium anode (1); a protective membrane architecture comprising a lithium ion conducting oxide having a garnet like structure; and a second electrode in ionic communication with the first electrode via the protective membrane architecture.    USE - As electrochemical device such as battery cell.    ADVANTAGE - The battery cells are capable of achieving high energy densities. The active species dissolved in the catholyte partake in the cell reaction, and discharge products form, that render the cathode compartment hygroscopic. By this expedient, the cathode compartment scavenges water from the ambient air during cell operation, and this facilitates a number of advantages, including: preventing dry out of the catholyte, prolonging the discharge, and enhancing the cell energy density (Wh/kg and Wh/l). Appropriate concentrations of active and non-active salts may impart a number of benefits to the cell, including rendering the cathode compartment hygroscopic during cell operation; effectuating, prior to initial discharge, a very low vapor pressure of water above the catholyte; enhancing or maintaining the conductivity of the catholyte at various stages of discharge, and stabilizing the protective membrane/catholyte interface during storage under open circuit conditions.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for battery cell (10) comprising a protected anode, comprising, a lithium anode having a first surface and a second surface, a protective membrane architecture on at least the first surface of the anode, a cathode compartment (4) comprising a cathode for reducing molecular oxygen and an aqueous catholyte comprising water and an active first substance material dissolved in it, where the catholyte, prior to initial discharge, has an equilibrium relative humidity of less than 50%; and, where the protective membrane architecture comprises at least one material configured to provide a first membrane surface chemically compatible with the alkali metal anode in contact with the anode, and a second membrane surface impervious to and chemically compatible with the components of the cathode compartment.    DESCRIPTION OF DRAWING(S) - The figures show Li/air battery cell in cross sectional and perspective depictions.    Lithium anode (1)    Electrolyte protective membrane (2)    Cathode compartment (4)    Lithium air battery cell (10)    Case (11)    Ports (12)