Recent advances in the development of sodium-sulphur batteries for load levelling and motive power applications

This paper describes some recent progress in the design and development of sodium/sulphur batteries for motive power applications. The historical development of cell designs over the last 10 yr is reviewed, and includes a discussion of development problems such as the durability of beta-alumina, and corrosion of the sulphur electrode current collector. The tubular electrolyte is now widely adopted as the preferred development option, and a computer analysis shows that a volumetric energy density of about 200 Wh/litre can be obtained in an optimum design of a battery including thermal insulation. An advanced cell design has been adopted in which sodium is fed into the anodic reaction zone by capillary wick. This design is well suited to the demands of motive power applications in which the stored energy has to be supplied at about the 2 h rate. The design also permits the use of large electrolyte tubes, at least 30 mm dia × 500 mm in length, and this reduces the battery manufacturing costs. A large number of experimental cells have been tested, and over 85% utilization of the sodium and sulphur active materials has been achieved for repeated cycling of developed electrode constructions.