Synthesis, structure and ionic conductivities of novel Li-ion conductor A3LixTa6 − xZrxSi4O26 (A = Sr and Ba)

The solid state oxide Li-ion conductors with high electrochemical stability as well as high ionic conductivity are needed for application to all-solid-state Li-ion battery. In this study, A3LixTa6 − xZrxSi4O26 (A = Sr and Ba) as the candidate solid electrolytes stable against Li metal were synthesized by a conventional solid state reaction, and their structure and ionic conductivities were investigated. Both the compounds with A = Sr and Ba crystallize in hexagonal structure with space group P6¯2m in the same as A3Ta6Si4O26 does. MEM analysis, first principles calculation, and NMR spectroscopy showed that Li ions reside in interstitial sites. The sample with A = Ba exhibits higher ionic conductivity (e.g. 6.9 × 10− 8 S cm− 1 at 500 K in x = 1.0) than that with A = Sr (e.g. 3.2 × 10− 8 S cm− 1 at 500 K in x = 1.0). Ionic conductivity was enhanced with an increase of the substitution of Li and Zr. Further enhancement of ionic conductivity was derived by making deficiencies at A site cation. Consequently, Ba2.75Li1.5Ta5ZrSi4O26 exhibits the highest total ionic conductivity of 4 × 10− 7 S/cm at 500 K and the lowest activation energy of 0.72 eV. The consideration of the size of bottlenecks and nudged elastic band calculations suggest that Li ions diffuse in the A-site deficient layer perpendicular to the c-axis.