The synergistic effect of Zn2+ doping and NaF interfacial melting aid increases the ionic conductivity of Na3Zr2Si2.2P0.8O12

Abstract

All-solid-state sodium batteries, renowned for their leak-proof nature and enhanced safety profile, have become a pivotal focus of research. Their viability hinges on the development of robust solid electrolyte materials. Among these, Na3Zr2Si2PO12 (NZSP) stands out as a particularly promising candidate. However, the practical utility of NZSP has been limited by its relatively modest room temperature conductivity. This paper introduces a novel modification strategy aimed at significantly enhancing room temperature conductivity of NZSP. In the series of experiments, NSZP was synthesized by traditional sintering process with Zn2+ doping and NaF additives. Through the substitution of Zr4+ ions with Zn2+ ions, this innovative approach not only raises the sodium ion concentration but also expands the bottleneck regions within the Na ion transport pathways. This augmentation ultimately translates into heightened grain conductivity. Additionally, the incorporation of NaF during the sintering process induces crystal growth in NZSP, thereby reducing grain boundary concentration and further amplifying grain conductivity's contribution to the overall ionic conductivity. Employing conventional sintering techniques, we successfully synthesized Na3.3Zr1.95Zn0.05Si2.2P0.8O12-0.25NaF (−0.25 NaF indicates that 0.25 mol NaF was added during sintering) electrolyte samples, which demonstrated an impressive high room temperature conductivity of 2.2 × 10−3 S cm−1. This value surpasses the ionic conductivity of undoped NZSP electrolytes by approximately an order of magnitude. Moreover, the Na3.3Zr1.95Zn0.05Si2.2P0.8O12-0.25NaF electrolyte exhibits a remarkable electrochemical window extending up to 4.9 V, accompanied by exceptional cycling stability. These properties render it an ideal candidate for a diverse array of cathode materials.