On the structural integrity of the spinel block in the β"-alumina structure.
The β''-alumina structure is examined in detail and an analysis is presented of the three-dimensional integrity of the lattice. The layer structure that is responsible for the very high sodium conduction rate is the specific focus. Rigid layers that are derived from the cubic spinel structure are interleaved by more open honeycomb pathways where rapid ion diffusion takes place. The three-dimensional rigidity of the spinel block in this structure makes it possible to accurately quantify the conduction layer thickness based only on the hexagonal unit-cell dimensions, as suggested originally by Harbach [(1983), J. Mater. Sci. 18, 2437-2452]. His calculation is tested rigorously against the many single-crystal structure determinations that have been made on the β''-alumina family compounds and excellent correlation is found.
High temperature sodium batteries: status, challenges and future trends
The progress in the research and development of high temperature sodium batteries suggests that all-solid-state batteries with inorganic or polymer solid electrolytes are promising power sources for a wide range of applications due to their high thermal stability, reliability, long-cycle life and versatile geometries. The electrolytes play a fundamental role in terms of current (power) density, the time stability, and the safety of batteries and, as a result, their continuous improvement and innovation are indeed critical to success. In fact, inorganic solid electrolytes pave the way for improving the cost-effective development of rechargeable sodium batteries. This review describes a state-of-the-art overview of most of the Na+ conductors for use as electrolytes in sodium/sulphur and ZEBRA batteries. The emphasis of this article is on inorganic solid electrolytes, especially, ceramic and glass-ceramic electrolytes as promising alternatives applicable to all solid-state batteries. As part of a continuous effort to find new materials that operate at room temperature and moderate temperatures, NASICON electrolytes will also be considered. Polymer electrolytes based on poly(ethylene oxide) (PEO) are also very suitable for all solid-state batteries. Hence, the review focuses on ion transport based on the observed conductivity, electrolyte preparation, safety and environmental impact.
The effect of quenching on the Na+ ion distribution in Na+ β″-alumina
Abstract A large single-crystal of Na + β″-alumina grown in the normal way by slow evaporation at 1675°C, and allowed to cool slowly was divided into two roughly equivalent parts. Each was subjected to a careful single-crystal neutron diffraction study at ambient temperature: the one as grown; the other after slow reheating to 1350°C and quenching. Chemical analyses of Na, Mg and Al content were made on both crystals after data-collection. Structural differences were observed in the Mg 2+ /Al 3+ ordering and more dramatically, in the Na + ion arrangement which lost all trace of short-range-order, becoming completely randomized after quenching. These differences can be related to effects observed earlier of similar heat-treatments on ionic conductivity in Na + β″-alumina.