Factors contributing to the breakdown of sodium beta alumina solid electrolytes

Thesis/Dissertation · Fri Jan 01 04:00:00 EST 1982

OSTI ID:6215283

Buechele, A C

Clarification of the breakdown process occurring during charge transfer in sodium beta alumina solid electrolytes was derived from: (1) studying the effects of molten sodium contact at 350/sup 0/C on single crystal sodium beta alumina and polycrystalline sodium beta'' alumina; (2) determination of critical current density by monitoring acoustic emissions accompanying crack growth in sodium/sodium beta'' alumina/sodium cells subjected to linear current ramping at 1 mA cm/sup -2/ sec/sup -1/; (3) failure analysis conducted on cycled electrolytes, some from commercial sodium/sulfur cells, which had been subjected to up to 703 Ahr cm/sup -2/ of charge transfer. Gray coloration developing in beta aluminas in contact with molten sodium was found to be a consequence of formation, through reduction by sodium, of oxygen vacancies charge compensated by electrons. Electronic conductivity of the electrolyte increases as a result. No second phase formation was detected. Colored electrolytes from sodium/sulfur cells show evidence of a newly recognized degradation mechanism in which fracture occurs when sodium is reduced and deposited internally under pressure as metal in regions where an electronic conductivity gradient exists. Critical current densities determined here by acoustic emission methods were substantially lower than those reported by other investigators. Critical current density was found to bear an inverse relation to average electrolyte grain size. Evidence of enhanced degradation was frequently found at 00.1 faceted boundaries of very large grains in cycled electrolytes. Evidence was also found in the cycled electrolytes for a slow crack growth mechanism and a progressive mode of degradation advancing from the sulfur electrode interface.

• OSTI ID: 6215283
• Country of Publication: United States
• Language: English

Related Subjects

25 ENERGY STORAGE
250903* -- Energy Storage-- Batteries-- Materials
Components
& Auxiliaries
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
BREAKDOWN
CHALCOGENIDES
CRITICAL CURRENT
CURRENT DENSITY
CURRENTS
ELECTRIC BATTERIES
ELECTRIC CONDUCTIVITY
ELECTRIC CURRENTS
ELECTRICAL PROPERTIES
ELECTROCHEMICAL CELLS
ELECTRODES
ELECTROLYTES
METAL-NONMETAL BATTERIES
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
SODIUM-SULFUR BATTERIES
SOLID ELECTROLYTES