Lithium ion conducting solid electrolytes for aqueous lithium-air batteries

Abstract

This article summarizes our research on solid electrolytes for rechargeable aqueous lithium-air batteries. Aqueous lithium-air batteries have potential application as a power source for electric vehicles, because of their high specific energy density. A water-stable lithium ion conducting solid electrolyte is the key material for lithium-air batteries to use lithium metal in aqueous circumstance. In this article, two types of lithium ion conducting solid electrolytes, NASICON-type Li1+xAxTi2-x-yGey(PO4)3 (A = Al, Fe) and garnet-type Li7-xLa3Zr2-xAxO12 (A = Nb, Ta) are introduced, and the conductivity behavior of these solid electrolytes by elemental substitution, their chemical stabilities in water and electrochemical stabilities with lithium metal are discussed. Lithium ion conductivities of 1.3 × 10-3 and 5.2 × 10-4S cm-1 at 25°C were observed in Li1.4Al0.4Ti1.4Ge0.2(PO4)3 and Li6.75La3Zr1.75Ta0.25O12, respectively. These solid electrolytes are unstable in water, but stable in saturated LiOH with saturated LiCl aqueous solution. The former solid electrolyte is unstable in contact with lithium metal, while the latter electrolyte shows stability against lithium metal.