Reuse of the surrounding powder used as a Na-source in the fabrication of sodium-beta–alumina solid electrolyte by vapor-phase conversion method

While Na/NiCl₂ secondary batteries offer high safety and excellent performance, their high price inhibits their commercialization. Two approaches are proposed to solve this problem: (1) automatic production by making cells of a flat plate structure and (2) lowering the price of sodium-beta-alumina solid electrolyte (BASE), a key component. In general, a thin and wide disk-type BASE for a planar Na/NiCl₂ battery is prepared from zirconia-toughened alumina (ZTA) by a vapor-phase conversion (VPC) process. In the process, Na-β″-Al₂O₃ powder, which is usually used as surrounding powder to supply sodium, is used once, then discarded. In this study, two methods were attempted to reduce the BASE cost fabricated by the VPC process. The first is the reuse of the surrounding powder in the VPC. The number of reuses has been up to three times. The second is that the surrounding powder is used as-is by mixing raw material powders, that is α-Al₂O₃, Na₂₋CO₃, and Li₂CO₃, instead of Na-β″-Al₂O₃ powder. This allows omission of the calcination process required for Na-β″-Al₂O₃ synthesis. Furthermore, the properties of the BASE prepared by VPC with the reused surrounding powder were analyzed, and their changes were investigated.