Porous papers and felts fabricated from BN and Y20~ fibers have been evaluated as electrode separators for Li-A1/LiC1-KC1/FeSx cells. The physical and mechanical properties were determined, and in-cell tests exceeding 1000 hr were conducted. The papers and felts had adequate strength and flexibility for cell assembly and performed well during cell testing. Results from the property measurements are presented and the performance of these materials in the cell tests is discussed.High temperature, molten salt Li-A1/LiC1-KC1/FeSx (x ~ 1 or 2) cells are being developed by Argonne National Laboratory (ANL) for electric vehicle propulsion and for energy storage on electric utility systems (1). One of the requirements for the successful development of cells for commercial applications is the identification of a low cost, porous electrode separator. The primary function of the electrode separator is to prevent direct electron flow between the electrodes without unduly restricting ionic flow through the electrolyte. In addition, separators for Li-A1/LiC1-KC1/ FeSx cells must retain the Li-A1 and FeSx active materials within the electrodes. This requirement is significant because the Li-A1 and FeSx are in the form of powders, and penetration of the separator by these fine particles may lead to a loss in cell capacity or electrical short circuits between the electrodes. The optimum structure and properties desired in the electrode separator have not been fully determined; however, the following general requirements must be satisfied: (i) The separator must be a good electrical insulator to prevent direct electron flow between the electrodes.(ii) It should be <2 mm thick to permit close electrode spacing, and it must contain a large volume of open porosity, probably >50%. These factors minimize the cell weight and the resistance to ionic flow between the electrodes. (iii) The pore channels should be <20 ~m diam to prevent penetration of the separator by the active powders in the electrodes. (iv) The separator must be chemically stable in the cell environment at the operating temperature (about 450~(v) The meChanical strength and flexibility must be sufficient to allow easy cell assembly, and to withstand the forces exerted on the separator by the volume changes which occur in the electrodes during cycling. (vi) The separator must have a potential cost of <$22/m 2 if the cost goals for a commercial cell are to be achieved.A flexible, fibrous ceramic appears to have the greatest potential for satisfying these requirements. At present, interest is centered on two ceramics, BN and Y203; both of these have proved to be compatible with the cell environment and are available in the form of fibers * Electrochemical Society Active Member. Key words: electrode separator, boron nitride, yttrium oxide, molten salt cell.(2). Boron nitride fabric is currently being used as a separator material, and engineering test cells with BN separators have been operated for periods up to 7800 hr (1, 3, 4). However, it does not appear that the cost goa...

The feasibility of using ceramic powders for electrode separators in lithium-aluminum/iron sulfide cells was evaluated. Test cells of two different designs were constructed and operated for periods of 1000 and 2000 hr. Thus, the powder separator appears to be a good candidate for use in commercial cells. The advantages and limitations of this type of separator are discussed, and a comparison is made with fibrous separators which are also being developed for these cells.Lithium-aluminum/iron sulfide batteries are being developed for stationary energy storage on electric utility systems and for electric-vehicle propulsion. Cells for this battery consist of a lithium-aluminum alloy negative electrode, an FeS or FeS2 positive electrode, and a molten LiC1-KC1 electrolyte (mp 352~ which requires an operating temperature of 400 ~ 450~ (1). An important factor in the successful development of these cells is the identification of an electrode separator which satisfies both the technical and economical requirements of the cell. In lithiumaluminum/iron sulfide cells the separator has two functions: (i) preventing electrical contact between the electrodes without unduly restricting ionic flow, and (if) providing a barrier which will retain the active materials of the cell within the electrodes. The latter is important because the active materials are generally in the form of fine powders. The optimum structure and properties desired in the electrode separator have not been fully determined; however, the following general requirements can be stated: (i) The separator must be a good electrical insulator to prevent direct electron flow between the electrodes. (if)The materials used in the separator must be chemically stable in the cell environment for the lifetime of the cell (5-10 yr). (iii) The separator should be <2 mm thick and contain a large volume of open porosity to minimize the cell weight and the resistance to ionic flow between the electrodes. (iv) The pore channels should be <20 ~m in diameter to prevent penetration of the separator by the active materials in the electrodes. (v) The integrity of the separator must be maintained during any dimensional changes which occur in the electrodes during cell operation. (vi) If commercialization of the cell is to be achieved, the separator must have a potential cost of <$22/m 2 and must permit rapid cell assembly.The requirement for a good electrical insulator precludes the use of metals in the separator. Most organic or polymeric materials are not stable at the cell operating temperature, and none of the polymers which have been tested in cells at ANL appear promising. Therefore, the choice of materials for the separator appears to be limited to ceramics. Chemical reaction with lithium in the cell environment severely limits the number of ceramics which can be used in the cell. A comparison of the free energies of formation of various oxide and nitride ceramics with the free energy of formation of Li20 and Li2N indicates that the following ceramics should be stable in the pr...

Die Eignung pulverförmiger keramischer Materialien wie z.B. BN, Si3N4, MgO oder CaO als Elektrodenseparatoren in Ketten des Typs A wird untersucht, indem Testzellen unterschiedlicher Konstruktion gebaut und für Perioden von 1000 und 2000 h betrieben werden.