Evaluation of plasma-sprayed CoS2 cathodes for thermal batteries
Conventional electroactive stack components in thermal batteries are constructed from pressed-powder parts. These include the anode, separator, and cathode pellets (discs). Pressing parts that are less than 0.010" thick is difficult. The use of plasma spray to deposit thin CoS/sub 2/ cathode films onto a stainless steel substrate was examined as an alternative to pressed-powder cathodes. The plasma-sprayed electrodes were tested in single cells under isothermal conditions and constant-current discharge over a temperature range of 400/spl deg/C to 550/spl deg/C using standard LiSi anodes and separators based on the LiCl-KCl eutectic. Similar tests were conducted with cells built with conventional pressed-powder cathodes, which were tested under the same conditions for comparative purposes. This paper presents the results of those tests.
Electrode Fabrication Processes for Thermal Batteries
Electrodes for conventional thermally activated (“thermal”) batteries are made by pressing of powders into pellets or discs. A thermal cell consists of pellets of a cathode (typically based on FeS2), a separator (based on halide eutectics), and an anode. Each cell incorporates a pyrotechnic to melt the electrolyte to activate the cell and bring it to operating temperature (typically, 500 – 600C). The activation temperature will depend on the melting point of the electrolyte. (The standard LiCl-KCl eutectic, for example melts at 352C.) Pelletizing of powders is very capital and labor expensive, which makes the production of thermal batteries expensive. Processing of powders involves many blending, drying, and granulation steps prior to pelletization and all work must be done in a dryroom environment where the relative humidity is maintained at <3%. Other ways of electrode fabrication have been examined in the past. Varta, for example, developed a tapecasting process using an organic binder for electrode fabrication for the Li-alloy/FeS2 system for secondary battery applications. The binder is thermally removed prior to battery assembly. Plasma (thermal) spraying has been examined as an alternative. Cathodes based on both FeS2 and CoS2 were successfully plasma sprayed onto a graphite-paper substrate with a number of halide-eutectic salts. Cathodeseparator composites were also prepared by this technique. However, plasma spraying must be done an inert-gas atmosphere with equipment that is fairly expensive. More recently, work at Electro Energy, Inc. (EEI) has demonstrated that thermal-battery electrodes can be prepared by a painting (spraying) process or doctor blading. Cathodes were painted onto a graphite-paper substrate using a conventional air gun. An aqueous slurry is used for painting,, which avoids the need for doing this in a dry room. This paper will discuss the history of electrode fabrication and the advantages and disadvantages of each technology along with future directions of electrode-fabrication technology. Examples of preliminary cathode fabrication studies at EEI will be presented.
SR topography of plastically deformed Fe-Si bicrystals - observation in situ and post mortem
SR reflection topography was applied to study the interaction of slip dislocations with the grain boundaries in Fe-4at%Si bicrystals deformed by compression. Three experimental settings with either a white or monochromatic beam were used and the corresponding orientation contrast analysed. Dislocation transmission through the grain boundary was observed in bicrystals with favourable geometry of the slip systems.