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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 Li 2 O 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 % La 2 Zr 2 O 7 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.

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Solid-state electrolytes are key materials for developing high-safety solid-state Li-ion batteries. The garnettype Li 7 La 3 Zr 2 O 12 (LLZO) solid electrolyte is one of the most promising solid electrolytes due to its high conductivity and feasible preparation in ambient air. Among several dopants, Tadoped LLZO (Ta-LLZO) delivers high stability against lithium metal and high conductivity, which attracts lots of researchers. However, production of Ta-LLZO ceramics is less problematic due to the complicated gas−liquid−solid sintering mechanism. This work aims to develop an efficient method to produce Ta-LLZO solid electrolyte ceramic pellets, including providing a stacking sintering method and optimizing the amount of excessive Li source, the wet milling duration, and the sintering temperature. First, a low-cost, efficient "gravel-separator" strategy is provided for multiple sintering of LLZO. Second, the Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 (Ta5) samples with different excessive Li levels (2, 4, 6, and 8%) are sintered at various sintering conditions of 1240 °C for 60 min, 1280 °C for 20 min, and 1320 °C for 2 min to search for the optimum excessive amount of Li. Third, Ta5 samples with optimized excessive Li (4, 6%) after milling for longer duration are sintered at 1280 °C for 30 min, 1300 °C for 10 min, 1320 °C for 10 min, 1320 °C for 30 min to finally optimize the preparation craft. After optimization, the Ta5 ceramics with excessive 4 and 6% Li sintered at 1320 °C for 10 min deliver homogeneous and dense crosssectional morphology, high conductivity of over 1 × 10 −3 S cm −1 at room temperature, and relative densities of above 96%. Furthermore, symmetric Li cells assembled with the Ta-LLZO solid electrolyte prepared with the optimized method deliver a critical current density of 1.28 mA cm −2 at 30 °C and over 1000 h of stable cycling at 0.2 mA cm −2 (0.2 mA h cm −2 ) at 30 °C.