Ga-ion migration during co-sintering of heterogeneous Ta- and Ga-substituted LLZO solid-state electrolytes

Abstract

Li₇La₃Zr₂O₁₂ (LLZO) is an attractive solid-state electrolyte for next-generation lithium solid-state batteries (SSB) because of its high ionic conductivity, and safety properties. Only the cubic LLZO phase has sufficient ionic conductivity, which is stabilized by substitution with elements like Ta or Ga. Ga-substituted LLZO has the highest ionic conductivity but is not stable towards metallic Li anodes, while Ta-substituted LLZO has a slightly lower conductivity but excellent reduction stability towards Li anodes. The combination of LLZO:Ga as a catholyte and LLZO:Ta as a ceramic separator for Li anodes would significantly enhance the performance of SSBs, but both materials have different processing parameters. In this work, the possibility of co-sintering LLZO:Ga|LLZO:Ta components is investigated with varying Li-excess of the LLZO:Ta phase, while the results are compared with pure references. The experiments showed a changed sintering activity, secondary phase formation, Ta- and Ga-ion diffusion, and a changed ionic conductivity when co-sintering LLZO:Ga|LLZO:Ta.