Phase evolution, structure, and electrochemical performance of Al-, Ga- and Ta- substituted Li7La3Zr2O12 ceramic electrolytes by a modified wet chemical route

Abstract

Garnet-type Li7La3Zr2O12 (LLZO) is one of the most promising solid-state electrolytes (SSEs) for advanced solid-state lithium batteries (SSLBs). In this work, Li6.25Al0.25La3Zr2O12, Li6.4Ga0.2La3Zr2O12, and Li6.4La3Zr1.4Ta0.6O12 ceramics are prepared by a modified wet chemical route. The composition of the black mixtures derived from the precursors is ascertained. The phase evolution and structural properties from the ceramic mother powders to the final ceramic electrolytes are discussed in detail. The characteristic of cubic LLZO with the space group I-43d arises in the Li6.4Ga0.2La3Zr2O12 ceramic electrolyte pellet after the secondary higher-temperature (1200 °C) sintering. The Rietveld refinement reveals the roles of Al3+ substitution at the Li+ sites and Ta5+ substitution at the Zr4+ sites to adjust crystal structure. In addition, the electrochemical performance of the ceramic pellets is also investigated. Remarkably, the Li6.4La3Zr1.4Ta0.6O12 ceramic electrolyte has the most outstanding electrochemical performance, showing the high ionic conductivity of 6.88 × 10−4 S cm−1 (25 °C), the low activation energy of 0.42 eV and an extremely low electronic conductivity of 1.77 × 10−8 S cm−1 (25 °C). Overall, it is supposed that this work may help to achieve high-quality modified LLZO ceramic electrolytes, especially using the wet chemical strategy.