Enhanced electrochemical properties of NASICON-type Na3Zr2Si2PO12 solid electrolytes with Tb3+-ions-assisted sintering

Abstract

The new-type NZSP solid-state electrolytes with enhanced ion transport properties were synthesized by using lanthanide rare-earth Tb3+ ions assisted-sintering. The Na3+xZr2-xTbxSi2PO12 (x = 0, 0.1, 0.2, 0.3, 0.4) solid-state electrolytes were characterized by X-ray diffraction analysis, scanning electron microscopy, and AC impedance testing. The effects of different Tb3+ contents on the phase composition, microstructure morphology, and electrochemical performance were investigated. The results showed that both Na3Zr2Si2PO12 and Na3Tb(PO4)2 phases are formed in the solid electrolytes by Tb3+-ions-assisted sintering. The formation of a new phosphate phase regulates the Si/P ratio of the dominant electric phase, enhances the Na+ occupation, and helps to enhance the mobility of sodium ions. The introduction of an appropriate amount of Tb3+ ions has a soldering-like effect, which can effectively improve the densification of ceramics and further improve the ionic conductivity by promoting grain fusion and reducing the grain boundary concentration. At room temperature, the ceramic with the composition Na3.2Zr1.8Tb0.2Si2PO12 exhibits a high relative density of 97.03% and the highest ionic conductivity of 6.32 × 10−4 S·cm−1 and with a low activation energy of 0.22 eV. In addition, the Na3Tb(PO4)2 grain boundaries phase with low electronic conductivity can limit the transfer of electrons and reduce the electronic conductivity of the NASICON electrolytes, so that the tolerance of solid-state electrolytes against Na dendrite growth is strongly enhanced. The Tb3+-ion-assisted sintering strategy can provide a valuable reference for improving the electrochemical performance of fast ion conductors.