β alumina, a typical solid electrolyte: Latest developments in fundamental approach and in battery utilization

In this article, the authors have concentrated on a typical material, β alumina, and they consider the various problems that are relevant to its utilization in advanced batteries. This involves the most recent developments in fundamental studies of this compound, mainly the connection between structure and conducting properties (ion correlation—vibrating and diffusing ions). However, the problems are now moving from research to engineering development, and in the second part of the article, a detailed consideration of β alumina and its behaviour in a sodium sulphur battery is given. Fundamental factors controlling the durability and viability of β alumina for this application are not properly understood yet, and some mechanisms are proposed to explain the failure or degradation of cells.