Ionic and Thermal Transport in Na-Ion-Conducting Ceramic Electrolytes

Abstract

AbstractWe have studied the ionic and thermal transport properties along with the thermodynamic key properties of a Na-ion-conducting phosphate ceramic. The system Na1+xAlxTi2−x(PO4)3 (NATP) with x = 0.3 was taken as a NASICON-structured model system which is a candidate material for solid electrolytes in post-Li energy storage. The commercially available powder (NEI Coorp., USA) was consolidated using cold isostatic pressing before sintering. In order to compare NATP with the “classical” NASICON system, Na1+xZr2(SiO4)x(PO4)3−x (NaZSiP) was synthesized with compositions of x = 1.7 and x = 2, respectively, and characterized with regard to their ionic and thermal transport behavior. While ionic conductivity of the NaZSiP compositions was about more than two orders of magnitude higher than in NATP, the thermal conductivity of the NASICON compound showed an opposite behavior. The room temperature value was about a factor two higher in NATP compared to NaZSiP. While the thermal conductivity decreases with increasing temperature in NATP, it increases with increasing temperature in NaZSiP. However, the overall change of this thermal transport parameter over the measured temperature range from room temperature up to 800 °C appeared to be relatively small.