Enhanced ionic conductivity of NASICON-type Na3Zr2Si2PO12 sodium-ion solid electrolyte via In doping

In-doped NZSP solid electrolytes were prepared via a modified solid-state reaction method. • The doping of In induces a monoclinic-to -rhombohedral phase transition. • In doping promotes the growth of grains, resulting in grain boundary reduction. • The Na 3.3 Zr 1.7 In 0.3 Si 2 PO 12 electrolyte shows the highest ionic conductivity of 1.24 mS/cm. NASICON-type Na 3 Zr 2 Si 2 PO 12 (NZSP) solid electrolytes are promising candidates for solid-state sodium-ion batteries (SSSIBs) owing to their high ionic conductivity, and excellent air stability. In this study, Na 3+x Zr 2-x In x Si 2 PO 12 (x = 0, 0.1, 0.2, 0.3, and 0.4) solid electrolytes were synthesized using a modified solid-state reaction method, and the effect of the In dopant content on the structure and properties of the NZSP electrolytes was investigated by XRD, SEM, and EIS. The introduction of In induces a monoclinic-to -rhombohedral phase transition. The rhombohedral phase has a large unit cell volume, which provides bigger channels for the conduction of Na ions. Moreover, In doping also promotes the growth of grains within the electrolyte, resulting in grain boundary reduction. The Na 3.3 Zr 1.7 In 0.3 Si 2 PO 12 electrolyte exhibits the highest ionic conductivity of 1.24 mS/cm at 30 °C, the lowest activation energy of 0.345 eV, and a negligible electronic conductivity of 1.81 × 10 −8  S/cm. A Na/Na 3.3 Zr 1.7 In 0.3 Si 2 PO 12 /Na symmetric cell shows an excellent cycling stability. These results demonstrate the good promise of Na 3.3 Zr 1.7 In 0.3 Si 2 PO 12 material as an alternative solid electrolyte for SSSIBs. Download: Download high-res image (446KB) Download: Download full-size image