The water-impermeable solid electrolyte is the key part to aqueous lithium secondary battery design at it serves as both separator and lithium-ion conducting pass way between the lithium metal anode and the aqueous electrolyte. Up to now, NASICON-type doped LiTi2(PO4)(3) solid lithium-ion conductors have been proved to be stable in an aqueous solution with a high content of lithium ions, but its relatively low robustness and high resistance is still a barrier towards fabricating high performance battery. Herein, a Li1.4Al0.4Ge0.2Ti1.4(PO4)(3) (LAGTP)-10 wt% TiO2 composite with a greatly reduced 90 mu m thickness was managed by the route of tape casting. The lithium-ion conductivity, bending strength and water penetration of the film were systematically investigated in this study. The electrical conduction of the film was 8.70 x 10(-4) s cm(-1) and the mechanical bending strength of the film was improved more than three times to 200 N mm(-2) measured at ambient temperature. Water impermeable function was realized by coupling a small amount of ca. 2 wt% epoxy resin into the open pores of the film. Finally, the assembled Li/Li(FSO2)(2)N in glyme/LAGTP-10 wt% TiO2-epoxy resin/10 M LiC1-1.5 M LiOH/MnO2, air cell presented a reduced total areal resistance to around 240 Omega cm(2) at 25 degrees C and was successfully cycled at 1.0 mA cm(-2) in air.