High lithium ion conductivity solid electrolyte of chromium and aluminum co-doped NASICON-type LiTi2(PO4)3

•NASICON-type solid electrolyte of Li1.4AlxCr0.4 − xTi1.6(PO4)3•Conductivity of 10− 3 S cm− 1 at room temperature•Stable in saturated LiOH with saturated LiCl aqueous solution•Electronic conduction is negligible small compared with ionic conductivity.

High lithium ion conductivity solid electrolytes of Li1 + xCrxTi2 − x(PO4)3 (x = 0–0.5) and Li1.4AlxCr0.4 − xTi1.6(PO4)3 (x = 0–0.4) with the NASICON-type structure were synthesized using a precursor prepared by the sol–gel method. The highest total electrical conductivity of 3.55 × 10− 4 S cm− 1 at 25 °C was obtained for x = 0.4 in Li1 + xCrxTi2 − x(PO4)3 (LACTP) sintered at 1120 °C for 6 h in air. Higher electrical conductivity was observed by the partial substitution of Cr3 + with Al3 +. The highest total electrical conductivity of 1.06 × 10− 3 S cm− 1 and bulk conductivity of 1.77 × 10− 3 S cm− 1 at 25 °C were obtained for x = 0.3 in Li1.4AlxCr0.4 − xTi1.6(PO4)3 sintered at 1070 °C for 6 h in air. The contribution of electronic conductivity to the total conductivity was negligibly small. Li1.4Al0.3Cr0.1Ti1.6(PO4)3 was unstable in water, but stable in saturated LiOH with saturated LiCl aqueous solution.