Water-stable lithium ion conducting solid electrolyte of iron and aluminum doped NASICON-type LiTi2(PO4)3

•A high lithium ion conductivity was observed in Li1.4Fe0.25Al0.15Ti1.6(PO4)3.•The conductivity at room temperature was 10-3 S/cm.•This compound was stable in the saturated LiOH and LiCl aqueous solution.

High lithium ion conductivity solid electrolytes of Li1.4FexAl0.4 - xTi1.6(PO4)3 (x = 0−0.4) with the NASICON-type structure were synthesized by using a sol−gel precursor. The highest electrical conductivity was obtained for Li1.4Fe0.25Al0.15Ti1.6(PO4)3 sintered at 1040 °C for 7 h in air. The total, grain boundary, and bulk conductivities of the pellet were 1.01 × 10-3, 2.17 × 10-3 and 1.81 × 10-3 S cm-1 at 25 °C, respectively. The contribution of electron (or hole) conductivity to the total conductivity was negligibly small. Li1.4Fe0.25Al0.15Ti1.6(PO4)3 was unstable in water, but stable in saturated LiOH and LiCl aqueous solutions.