Microstructural and mechanical characterization of Na1+xHf2Si2.3P0.7O10.85+0.5x and Na1+xZr2P3-xSixO12 NASICON-type solid electrolytes

NASICON-type solid electrolytes are promising materials for novel solid-state-batteries aiming toward high energy densities. Na1+xHf2Si2.3P0.7O10.85+0.5x with varying sodium content as well as Sc- or Mg-doped and undoped Na1+xZr2P3-xSixO12 were synthesized by solution-assisted solid-state reaction. Microstructural and mechanical characteristics as well as conductivities were investigated. The electrochemical and microstructural properties of all studied materials appear to be highly affected by the sodium content glassy phase and secondary phase formation as well as bloating. The mechanical properties of the specimens depend mainly on microstructural characteristics. Our findings indicate improved mechanical behavior is achieved when bloating and secondary phase formation are inhibited. However, possible influences of glassy phase content on the material properties need to be further investigated.