Enhanced ionic conductivity in Na3Zr2Si2PO12 NASICON-type solid electrolytes by adding Mg2+-ions

The unique NASICON-type 3D structure of Na3Zr2Si2PO12 (NZSP) material offers ideal Na+ conductivity at high temperatures, making it a subject of widespread interest among researchers in fields such as solid state batteries and solid state capacitors. However, the low-symmetry monoclinic phase structure and high grain boundary resistance of NZSP limit its ionic conductivity and application at room temperature. In this work, we optimize Na+ conductivity of NZSP by doping bivalent Mg2+ (~ 2.4 × 10-3 S/cm, when x = 0.25). The analysis reveals that this way increases the content of the R3c phase which has a higher ionic conductivity and reduces grain boundary resistance. Simultaneously, the internal voids of NZSP decrease along with the original square-like grain size. and the more spaces for Na+ transport are provided because the cell volume of NZSP can be effectively enhanced by doping Mg2+. In addition, the doped samples exhibit electronic conductivity 4 to 5 orders of magnitude lower than their ionic conductivity. This investigation provides some references for the mechanism of ionic conductivity regulation and the technical production of NASICON-type ceramic eletrolytes.