Exploring the origin of ZrO2 phase in Na3Zr2Si2PO12 ceramic electrolyte

The development of solid-state batteries based on NASICON-type Na3Zr2Si2PO12 (NZSP) ceramic electrolytes is critically hampered by their unfavorable room temperature ionic conductivity. Moreover, the inadvertent appearance of ionic insulator ZrO2 phase within NZSP matrix constantly bothers these relevant researches. In this work, via utilizing different kinds of starting materials, it is found that the kinds of Zr source and sintering temperature can regularly affect the relative content of ZrO2 in the NASICON matrix. More significantly, it reveals that there is no direct correlation between the ZrO2 content and the room temperature ionic conductivity of NZSP. Moreover, NZSP obtained at 1150 °C via solid-state reaction with Na2CO3, ZrO2, SiO2, and NH4H2PO4 as starting materials can achieve a room temperature conductivity of 9.1 × 10−4 S cm−1, which is a relatively high value. The work here offers a thorough understanding of the origin of ZrO2 phase in NASICON as well as guidance for the mass production of NASICON-type ceramic electrolytes via conventional solid-sate reaction.