Composite solid-state electrolytes, devices with composite solid-state electrolytes, and methods for fabrication thereof

A method comprising:

• (a) providing one or more precursors on a first surface of a porous support layer;
• (b) subjecting the porous support layer with one or more precursors to a first temperature for a first time so as to sinter the one or more precursors to form a porous scaffold, the first time being less than or equal to about 60 seconds, the porous scaffold comprising an ion-conducting oxide;
• (c) providing one or more filler materials on a second surface of the porous scaffold, the one or more filler materials having a melting point in a range of 500-1100 K, inclusive;
• and
• (d) subjecting the porous scaffold with the one or more filler materials to a second temperature for a second time so as to melt the one or more filler materials to form a non-porous composite solid-state electrolyte layer with the one or more filler materials infiltrating the porous scaffold, the second time being less than or equal to about 60 seconds.