The development of electrolytes with high ionic conductivity and stable electrode–electrolyte interfaces is crucial for the practical realization of solid-state sodium batteries. In this study, the effect of heteroatom doping in a von-Alpen-type Na super ionic conductor (NASICON) was investigated by substituting Zr⁴⁺ with Mg²⁺, Zn²⁺, and La³⁺ to enhance its material properties and evaluate its potential for solid-state sodium battery applications. Computational chemistry was employed to predict the thermodynamic stability influenced by dopant introduction and the changes in ionic conductivity arising from crystal structure distortion, with the predictions validated by experiments. The optimized Zn²⁺-doped NASICON (Zn-NZSP0.07) exhibited the highest total ionic conductivity of 2.74×10⁻³ S∙cm⁻¹, representing a 4.5-fold increase compared with undoped NASICON (6.00×10⁻⁴ S∙cm⁻¹). The material also showed a high relative density of 99.1%, indicating a compact and well-sintered microstructure, as confirmed by a three-point bending test. Furthermore, a high critical current density of 1.4 mA∙cm⁻² was achieved in symmetric cell testing. Additionally, a Na₃V₂(PO₄)₃||Zn-NZSP0.07||Na cell delivered an initial capacity of 103.9 mAh∙g⁻¹ at 0.1 A∙g⁻¹ and retained 73.4% of its capacity after 200 cycles. These results demonstrate that optimal heteroatom doping is crucial for enhancing the performance of NASICON.

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 (Mg²⁺) as a heterogeneous element. The optimal Mg-doped vA-NASICON exhibited a high ionic conductivity of 3.64×10⁻³ S·cm⁻¹, 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 Mg²⁺ was used in a synthetic process, the relative density (96.6%) and grain boundary ionic conductivity (σ_gb) were maximized, which improved the total ionic conductivity (σ_t) of the vA-NASICON. However, when Mg²⁺ was introduced in excess, the ionic conductivity decreased because of the formation of an undesired sodium magnesium phosphate (Na_xMg_yPO₄) 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.