Effect of Nb and Ta Simultaneous Substitution on Self-Consolidation Sintering of Li7La3Zr2O12

Garnet Li7La3Zr2O12 (LLZO) has been a prospective solid electrolyte with high ionic conductivity and a wide electrochemical window. Different from conventional cold or hot isostatic pressing methods, a self-consolidation strategy without any pressing assistance was proposed to prepare dense LLZO. In this work, simultaneous substitution of Nb2O5 and Ta2O5 was attempted to further explore the mechanism of self-consolidation sintering. The influence of the Nb2O5 and Ta2O5 substitution amount on the crystalline phase, morphology, and ionic conductivity was investigated. Due to the different melting points and thermal behaviors of Nb2O5 and Ta2O5, the endothermic peak corresponding to sintering became weaker, which was associated with the self-consolidation process of LLZO. Accordingly, larger grain sizes and fewer grain boundaries were observed in LLZO when the amounts of Nb2O5 and Ta2O5 were both 0.25 mol. This indicates that the simultaneous substitution of different cations plays a vital role in self-consolidation sintering, which contributes to facilitating the grain growth and reducing the amount of grain boundaries. This work emphasizes the key role of the dopant melting point and thermal behavior in sintering, suggesting an alternative way of substitution for LLZO electrolyte preparation.