SODIUM SULPHUR CELLS, CATHODE STRUCTURES THEREFOR, AND THE MANUFACTURE OF SUCH CELLS AND STRUCTURES

摘要

In a sodium sulphur cell, having a cathode structure 15 (Figure 1) between a cathode current collector 14 and a solid electrolyte 10, the cathode structure is formed of a fibre material with at least 90% of mesophase-pitch-based carbon fibre material with the fibres oriented in two dimensions parallel to the plane of a mat, the mat then being needle-punched to re-align fibres and so increase the electrical conductivity transverse to the plane of the mat. Preferably up to 10% of a material having a greater resistance to bending is incorporated before needling; these may be carbon fibres which are non-mesophase-pitch-based. Alumina or other electrically non-conductive fibres may alternatively or additionally be incorporated. These further fibres can be chosen to improve the resilience of the cathode structure. The mat is impregnated with the cathodic reactant, i.e. sulphur or sodium polysulphides, in liquid form and cooled while compressed to solidify the reactant and form a rigid unit for insertion in the cell, which unit will expand when the reactant is liquified at the operating temperature.