Li7La3Zr0.5Nb0.5Ta0.5Hf0.5O12 High-Entropy Li-Garnet with Fine Microstructure and Promising Properties

Abstract

We demonstrated the processing of Li7La3Zr0.5Nb0.5Ta0.5Hf0.5O12 high-entropy Li-garnet with promising properties for lithium batteries. We first synthesized the LLZNTH Li-garnet powders which have a single cubic garnet phase without any secondary phases as well as uniform elements distributions. We further studied the formation, sintering, and mechanical properties of Li7La3Zr0.5Nb0.5Ta0.5Hf0.5O12 (LLZNTH) high-entropy Li-garnet with the comparison with Li6.75La3Zr1.75Ta0.25O12 (LLZT). The study indicates that the LLZNTH sample has a finer particle size after both calcination and ball mill than LLZT. Both samples can be densified to a relative density up to ~93-94% at a temperature of 1100°C, however, they show significant different sintering and grain growth behaviors. The LLZNTH sample takes 16 hours to reach the maximum relative density while the LLZT sample only needs 12 hours. LLZNTH sample has a significant lower grain growth parameter due to sluggish effects of high-entropy compounds so that it maintains fine microstructures (grain size ~10µm) than the LLZT sample (grain size over 100 µm). Due to the fine microstructures, the LLZNTH sample shows both higher flexural strength (84.8±6.9MPa compared with 47.9±10.1MPa) and hardness (8.5±0.8GPa compared with 7.7±0.4GPa) than the LLZT sample. Ionic conductivity characterizations indicate that the LLZNTH sample shows a moderate conductivity of 4.67×10-4 S cm-1 at room temperature and a low activation energy of 0.25eV. Figure 1