Beta-alumina electrolyte for use in sodium/sulphur batteries Part 2. Manufacture and use

Abstract

Part 1 of this two-part review was concerned with the fundamental chemical and physical properties of sodium beta-alumina. In Part 2 we consider the ceramic science and technology involved in the manufacture of electrolyte tubes and their use in sodium/sulphur batteries. The specification set for β-alumina tubes is first outlined, followed by a review of the fabrication procedures which have been employed. The problems of quality control and the elimination of flaws are emphasised. Mechanical and thermal expansion data which have been measured for β-alumina ceramics are discussed. The surface interaction effects between the electrolyte and the electrode materials (sodium and sulphur) are considered, and it is suggested that wetting effects are important in determining both the cell resistance and the life span of the electrolyte in use. The failure modes of β-alumina electrolyte tubes fall into three categories — electrical breakdown, mechanical shock, and thermo-mechanical failure — but in a real situation these may be interactive. Electrical breakdown may be either a result of localised high current densities during recharge or a consequence of too high an imposed voltage at top of charge (dielectric breakdown). Published work on these failure modes is reviewed. Finally, the present state-of-the-art in manufacturing β-alumina electrolyte tubes is summarised, and the need for further research and development on improving their durability is noted. As one component of a system — the Na/S cell — the electrolyte cannot be viewed in isolation and its durability is a function both of its perfection of manufacture and the conditions of use in the cell.