Improving ionic conductivity of von-Alpen-type NASICON ceramic electrolytes via magnesium doping
Il-Seop Jang, Wooseok Go, Bo-Ye Song, Hayoung Park, Yun Chan Kang, Jinyoung Chun
Abstract
NASICON (sodium (Na) superionic conductor) compounds have attracted considerable attention as promising solid electrolyte materials for advanced Na-based batteries. In this study, we investigated the improvement in ionic conductivities of von-Alpen-type NASICON (vA-NASICON) ceramic electrolytes by introducing a magnesium ion (Mg<sup>2+</sup>) as a heterogeneous element. The optimal Mg-doped vA-NASICON exhibited a high ionic conductivity of 3.64×10<sup>−3</sup> S·cm<sup>−1</sup>, which was almost 80% higher than that of un-doped vA-NASICON. The changes in physicochemical properties of the vA-NASICONs through the Mg introduction were systematically analyzed, and their effects on the ionic conductivities of the vA-NASICON were studied in detail. When the optimal ratio of Mg<sup>2+</sup> was used in a synthetic process, the relative density (96.6%) and grain boundary ionic conductivity (<i>σ</i><sub>gb</sub>) were maximized, which improved the total ionic conductivity (<i>σ</i><sub>t</sub>) of the vA-NASICON. However, when Mg<sup>2+</sup> was introduced in excess, the ionic conductivity decreased because of the formation of an undesired sodium magnesium phosphate (Na<sub><i>x</i></sub>Mg<sub><i>y</i></sub>PO<sub>4</sub>) secondary phase. The results of this study are expected to be effectively applied in the development of advanced sodium-based solid electrolytes with high ionic conductivities.