Sol-gel synthesis of Mg2+ stabilized Na-β"/β-Al2O3 solid electrolyte for sodium anode battery

Mg2+ stabilized Na-beta"/beta-Al2O3 powder was successfully synthesized by a sol-gel method using PVP-10000 as complexing agent and metal nitrates as corresponding metal sources. The thermal decomposition of the xerogel and the evolution of crystallization behavior of Na-beta"/beta-Al2O3 were studied. The obtained powders have been unambiguously characterized using X-ray diffraction (XRD), N-2 adsorption, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The Mg2+ stabilized Na-beta"/beta-Al2O3 crystallized gradually from amorphous phase to metastable intermediate phases and further formed the major phase at 1000 degrees C. The results showed that the large surface area of the amorphous intermediate phase with mesoporous structure followed by the generation of intermediate phases named as m-Al2O3 and MgAl2O4 with spinel structure to a great extent promoted the formation of Na-beta"/beta-Al2O3 phase. The Na-beta"/beta-Al2O3 nano-powders exhibited a plate-like two dimensional structure with clear crystallographic plane for Na+ diffusion. The transformation from m-Al2O3 only required the shift of Na+ from alternate layers of oxygen and the accommodation of every fifth layer since the structure of m-Al2O3 is only slightly different from that of Na-beta"/beta-Al2O3. The relative density of the sintered ceramic was approximately 98.8% and the ionic conductivity can reach 0.24 S cm(-1) at 350 degrees C. (C) 2014 Elsevier B.V. All rights reserved.