THIN NA-BETA-ALUMINA ELECTROLYTES BY ELECTROCHEMICAL VAPOR DEPOSITION (EVD) FOR SODIUM-SULFUR BATTERIES

NA-BETA-ALUMINA IS THE SOLID ELECTROLYTE MEMBRANE USED IN SODIUM-SULFUR BATTERIES WITH APPLICATIONS IN LOAD LEVELING, ELECTRIC AUTOMOBILES, AND SATELLITE COMMUNICATIONS. THE STATE-OF-THE-ART ELECTROLYTES ARE FABRICATED BY GREEN-FORMING FOLLOWED BY SINTERING AT ~1540 DEGREES CENTIGRADE. ENCAPSULATION IN PLATINUM CONTAINERS OR MAGNESIA CRUCIBLES IS NECESSARY TO PREVENT LOSS OF SODA. TYPICAL THICKNESS IS ~1.5 MM WITH THE ELECTROLYTE SPECIFIC RESISTANCE ~0.6 OMEGA CM(2) WHICH CONSTITUTES ~40 OR 50 PERCENT OF THE NET CELL SPECIFIC RESISTANCE. TO ACHIEVE HIGH CHARGE/DISCHARGE CURRENT DENSITIES AND HIGH ENERGY EFFICIENCY, ELECTROLYTE MEMBRANES OF MUCH SMALLER THICKNESS ARE NECESSARY. RESEARCHERS ARE INVESTIGATING A NOVEL METHOD FOR THE FABRICATION OF THIN (20 TO 50) UM) NA-BETA-ALUMINA SOLID ELECTROLYTES. THIS METHOD, KNOWN AS ELECTROCHEMICAL VAPOR DEPOSITION (EVD) HAS BEEN USED SUCCESSFULLY TO DEPOSIT ZIRCONIA, PEROVSKITES, AND CERIA FOR APPLICATIONS IN SOLID OXIDE FUEL CELLS. THE METHOD CONSISTS OF REACTING GASEOUS SPECIES TO FORM A THIN MEMBRANE OF NA-BETA-ALUMINA OVER A POROUS SUPPORT, FURTHER GROWTH OF WHICH OCCURS BY EVD. AN EVD REACTOR IS BEING BUILD. NA-BETA-ALUMINA MEMBRANES ARE DEPOSITED USING A ONE STEP AND A TWO STEP PROCESS. THE MEMBRANES ARE CHRACTERIZED WITH REGARDS TO MICROSTRUCTURE, CRYSTAL STRUCTURE, AND CONDUCTIVITY.