Developing Preparation Craft Platform for Solid Electrolytes Containing Volatile Components: Experimental Study of Competition between Lithium Loss and Densification in Li7La3Zr2O12

Li7La3Zr2O12 (LLZO) is one of the most promising candidate solid electrolytes for high-safety solid-state batteries. However, similar to other solid electrolytes containing volatile components during high-temperature sintering, the preparation of densified LLZO with high conductivity is challenging involving the complicated gas–liquid–solid sintering mechanism. Further attention on establishing low-cost laborastory-scale preparation craft platform of LLZO ceramic is also required. This work demonstrates a "pellet on gravel" sintering strategy, which is performed in a MgO crucible and box furnace under ambient air without any special equipment or expensive consumables. In addition, the competition between lithium loss from the sintering system and internal grain densification is critically studied, whereas the influences of particle surface energy, Li-loss amount, and initial excess Li2O amount are uncovered. Based on the sintering behavior and mechanism, optimized craft platform for preparing dense LLZO solid electrolytes including mixing, calcination, particle tailoring and sintering is provided. Finally, exemplary Ta-doped LLZO pellets with 2 wt % La2Zr2O7 additives sintered at 1260–1320 °C for 20 min deliver Li+ conductivities of ∼9 × 10–4 S cm–1 at 25 °C, relative densities of >96%, and a dense cross-sectional microstructure. As a practical demonstration, LLZO solid electrolyte with optimized performance is applied in both Li–Li symmetric cells and Li–S batteries. This work sheds light on the practical production of high-quality LLZO ceramics and provides inspiration for sintering ceramics containing volatile compounds.