Investigation of High Temperature Battery Systems

Abstract : Hermetically sealed sodium-sulfur cells intended to operate at 300 C in atmospheric environment and to deliver 10 A for 2 hr above 1.0 V for 100 cycles with a specific power and specific energy of 110 W/kg and 110 W hr/kg, respectively, were designed and fabricated. The cells were to withstand five thermal cycles from operating temperature to room temperature without loss of electrical performance. These cells utilized a disk shaped magnesium oxide- enriched beta-alumina electrolyte with low cost materials for cell containers. The seals used in the cell were all based on state-of-the-art technology and comprised a glass sealant between the beta-alumina electrolyte and the alpha- alumina rings, copper braze between the alpha-alumina rings and the Kovar cell containers, and laser welds between the Kovar cell containers and the stainless steel cell cover. Chromium plasma coating was used to protect the copper braze and Kovar against corrosion by sulfur and/or sodium polysulfide. No catastrophic cell failure due to cell design or materials of construction has been observed during testing of a cell for over 800 hr.