Application of beta-alumina to Na-S storage batteries

Results of experimental work concerning the development of sintered beta-alumina for use as solid electrolytes and porous cathode current collectors in a sodium-sulfur storage battery are presented. Beta-alumina closed-end tubes for use in cells in which the Na electrode is centrally located were fabricated by various molding and sintering procedures with the addition of Ta2O5 to the original powder, and the conditions necessary for reaction sintering from alpha-alumina were determined. Evaluation of the properties of carbon cloth, carbon felt, graphite felt, a loose-stitch graphite braid tube and a knitted cloth of high elastic modulus carbon fibers as porous current collectors reveals that only knitted carbon fiber cloth maintained its capacity at the end of 100 cycles. This porous material was then used to investigate the lifetimes and capacities of the various ceramic tubes in three different cell designs and their failure modes. Results for the Na-centered cells indicate that the cycle life of beta-alumina ceramic solid electrolytes depends on the uniformity of ceramic microscopic density as well as its resistivity to sodium sulfide, which in turn depend on molding and sintering techniques.