Double influence of CaF2 addition on microstructure and conductivity of NASICON-type Na3Zr2Si2PO12 solid electrolytes

Abstract

The Na₃Zr₂Si₂PO₁₂-xCaF₂ (x = 0, 0.05, 0.10, 0.15, 0.20) solid electrolytes were synthesized using the conventional solid-state reaction method. The impact of CaF₂ content on the structure and properties of Na₃Zr₂Si₂PO₁₂ was examined through XRD, SEM, XPS, and EIS analyses. The test results show that Ca²⁺ ions replace Zr⁴⁺ sites during the sintering process, increasing the cell volume and Na⁺ ion concentration. Meanwhile, CaF₂ improves the sintering properties of Na₃Zr₂Si₂PO₁₂ and promotes grain growth, thus reducing defects such as grain boundaries, voids, and holes. In this study, the role of CaF₂ doping in regulating the electron distribution and the effect on the Na⁺ ions migration energy barrier were also analyzed by density functional theory, which provided theoretical support for the experimental results. Ultimately, the Na₃Zr₂Si₂PO₁₂–0.1CaF₂ solid electrolyte exhibited a high ionic conductivity of 0.68 mS cm⁻¹ at room temperature. This work offers a valuable reference for the development of the next generation of all-solid-state batteries.