Sol-gel synthesis of Mg~(2+) stabilized Na-β'/β-Al_2O_3 solid electrolyte for sodium anode battery

摘要

Mg~(2+) stabilized Na-β"/β-Al_2O_3 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-β"/β-Al_2O_3 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 Mg~(2+) stabilized Na-β"/β-Al_2O_3 crystallized gradually from amorphous phase to metastable intermediate phases and further formed the major phase at 1000 °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-Al_2O_3 and MgAl_2O_4 with spinel structure to a great extent promoted the formation of Na-β"/β-Al_2O_3 phase. The Na-β"/β-Al_2O_3 nano-powders exhibited a plate-like two dimensional structure with clear crys-tallographic plane for Na~+ diffusion. The transformation from m-Al_2O_3 only required the shift of Na~+ from alternate layers of oxygen and the accommodation of every fifth layer since the structure of m-Al_2O_3 is only slightly different from that of Na-β"/β-Al_2O_3. The relative density of the sintered ceramic was approximately 98.8% and the ionic conductivity can reach 0.24 S cm~(-1) at 350 °C.