The lithium ion conducting solid lithium phosphorous nitride (UPON) has been sputtered on the water-stable NASICON-type lithium ion conducting solid electrolyte Li1+x+yAlxTi2-xP3-ySiyO12 (LATP). The stability and the interface resistance of the Li-Al/LiPON/LATP/LiPON/Li-Al cell have been examined. It is shown that the UPON film protects LATP from reacting with the Li-Al alloy. The impedance of the Li-Al/LiPON/LATP/LiPON/Li-Al cell has been measured in the temperature range 25-80 degrees C. The total cell resistance is about 8600 Omega cm(2) at room temperatureand 360 Omega cm(2) at 80 degrees C. The analysis of the impedance profiles suggests that the Li-Al/LiPON interface resistance is dominant at lower temperatures. The LATP plate immersed in water for I month shows only a slight degradation in the conductivity. (C) 2008 Elsevier B.V. All rights reserved.