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Synthesis of nano-scale fast ion conducting cubic Li Report Title A solution-based process was investigated for synthesizing cubic Li7La3Zr2O12 (LLZO), which is known to exhibit the unprecedented combination of fast ionic conductivity, and stability in air and against Li. Sol–gel chemistry was developed to prepare solid metal–oxide networks consisting of 10 nm cross-links that formed the cubic LLZO phase at 600 degrees C. Sol–gel LLZO powders were sintered into 96% dense pellets using an induction hot press that applied pressure while heating. After sintering, the average LLZO grain size was 260 nm, which is 13 times smaller compared to LLZO prepared using a solid-state technique. The total ionic conductivity was 0:4 mS cm1 at 298 K, which is the same as solid-state synthesized LLZO. Interestingly, despite the same room temperature conductivity, the sol–gel LLZO total activation energy is 0.41 eV, which 1.6 times higher than that observed in solid-state LLZO (0.26 eV). We believe the nano-scale grain boundaries give rise to unique transport phenomena that are more sensitive to temperature when compared to the conventional solid-state LLZO. Synthesis of nano-scale fast ion conducting cubic Li Approved for public release; distribution is unlimited. 64834.2-CH REPORT DOCUMENTATION PAGE (SF298) (Continuation Sheet) Continuation for Block 13