Liquid sintering of garnet electrolytes by lithium germanate: Properties and interfacial performance with lithium anode

Garnet electrolytes have been approved widespread as one of the most competitive candidates in all solid state lithium batteries (ASSLBs). Herein, dense Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) ceramics were successfully produced via liquid sintering method by introducing 1 wt% 3Li₂O-2GeO₂ additive at reduced sintering temperatures for a shortened process period compared to solid method in air atmosphere. Relationships among sintering temperature, microstructure, densities, mechanical properties and electrical performance of the ceramics were explored concretely. The ceramics can be well densified and modified microstructurally at the appropriate sintering temperature, making the ionic conductivity significantly promoted. Mechanical properties would be enhanced as well, resulted to a compact and tough ceramic surface. Hence, a good-contacted, homogeneous and electrochemically stable electrolyte/Li interface can be fabricated. The LLZTO-1 wt% (3Li₂O-2GeO₂) composite electrolyte sintered at 1160 °C for 3 h exhibits the best comprehensive properties, the ionic conductivity and critical current density (CCD) of which reach 6.27 × 10⁻⁴ S·cm⁻¹ and 0.5 mA·cm⁻² at 25 °C. The improved interfacial performance enables the Li|LLZTO-1 wt% (3Li₂O-2GeO₂)|Li symmetrical cells and the LiFePO₄|LLZTO-1 wt% (3Li₂O-2GeO₂)|Li cells a good cycling performance at different current densities.