Large Planar Na-β″-Al₂O₃ Solid Electrolytes for Next Generation Na-Batteries

Large diameter (> 100 mm) planar Na-β″-Al₂O₃ solid electrolytes (BASE) with thickness from 1.0 to 1.5 mm have been prepared. Na-β″-Al₂O₃ was processed as a slurry and cast to give several meters of tape. One hundred and forty mm diameter discs were punched from the tape, stacked, and laminated with a large hydraulic press. Binder burnout and sintering were performed in 150 mm diameter MgO spinel encapsulations to mitigate the loss of Na₂O vapor. Conductivity and flexural strength were measured on smaller Na-β″-Al₂O₃ samples produced via the same tape casting process followed by sintering and gave results consistent with BASE materials produced by uniaxial pressing of powders. Planar BASE membranes enable new cell designs, which are predicted to have higher power densities and better stacking efficiency compared to currently manufactured tubular cells.