Tape-Cast Water-Stable NASICON-Type High Lithium Ion Conducting Solid Electrolyte Films for Aqueous Lithium-Air Batteries

A Li1.4Al0.4Ge0.2Ti1.4 (PO4)3 (LAGTP) film was prepared by a tape-casting method using a fine LAGTP powder prepared by the sol-gel method. A LAGTP composite film formed with approximately 2 wt% epoxy resin was water-impermeable and had high mechanical strength. The highest lithium ion conductivity of 5.26 × 10−4 S cm−1 at 25°C was obtained for the LAGTP-epoxy resin composite film. The LAGTP-epoxy resin composite film was stable in an aqueous solution with a high content of lithium ions. The three-point bending strength of the 75 μm thick LAGTP-epoxy resin composite film was 125 N mm−2. The water-impermeable composite film with excellent mechanical properties is an attractive candidate for the water-stable lithium electrode in rechargeable aqueous lithium-air batteries.