Demonstration of the Reproducibility Challenges in the Sintering Behavior of Lithium‐Stuffed Garnets in Scaling up Synthesis

ABSTRACT Lithium‐stuffed garnets, such as Li ₇ La ₃ Zr ₂ O ₁₂ (LLZO), are promising candidates for next‐generation solid‐state batteries because of their high room‐temperature ionic conductivity and chemical stability against lithium metal anodes, which are crucial for achieving higher energy density. However, realizing LLZO's potential in practical devices requires synthesis methods that can be scaled reliably to large batch sizes for manufacturing. Herein, we investigate the sintering reproducibility of LLZO synthesized at larger scales using ultrasonic spray pyrolysis, a cost‐effective and scalable synthesis route. Two 100 g batches of Al‐doped LLZO are prepared and their sintering behavior is examined in detail. Both Al‐LLZO batches contain over 90 wt.% cubic‐phase LLZO, and both batches exhibit room temperature conductivities greater than 1 × 10 ⁻⁴ S cm ⁻¹ at a relative density above 0.8. However, variations in secondary phases and subtle differences in Al content lead to significant differences in densification and microstructure. These results demonstrate that LLZO's sintering behavior is highly sensitive to small changes in secondary phases and Al content, creating reproducibility challenges when moving from laboratory‐ to manufacturing‐scale synthesis.