The Effect of Lithia Addition on the Sodium Ion Conductivity of Vapor Phase Converted Na-β"-alumina/YSZ Solid Electrolytes

Abstract

Na-β"-Al2O3 has been widely employed as a solid electrolyte for high-temperature sodium (Na) beta-alumina batteries (NBBs) thanks to its superb thermal stability and high ionic conductivity. Recently, a vapor phase conversion (VPC) method has been newly introduced to fabricate thin Na-β"-Al2O3 electrolytes by converting α-Al2O3 into β"-Al2O3 in α-Al2O3/yttriastabilized zirconia (YSZ) composites under Na+ and O2- dual percolation environments. One of the main challenges that need to be figured out is lowered conductivity due to the large volume fraction of the non-Na+-conducting YSZ. In this study, the effect of lithia addition in the β"-Al2O3 phase on the grain size and ionic conductivity of Na-β"-Al2O3/YSZ solid electrolytes have been investigated in order to enhance the conductivity of the electrolyte. The amount of pre-added lithia (Li2O) precursor as a phase stabilizer was varied at 0, 1, 2, 3, and 4 mol% against that of Al2O3. It turns out that ionic conductivity increases even with 1 mol% lithia addition and reaches 67 mS cm-1 at 350 oC of its maximum with 3 mol%, which is two times higher than that of the undoped composite.