Preparation and Characterization of Nanostructured FeS 2 and CoS 2 for High-Temperature Batteries
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Preparation and Characterization of Nanostructured FeS2 and CoS2 for High-Temperature Batteries Ronald A. Guidotti1, Frederick W. Reinhardt1 Jinxiang Dai2, and David E. Reisner2 Sandia National Laboratories, P.O. Box 5800, Albuquerque, NM 87185-0614 2 US Nanocorp®, Inc., 74 Batterson Park Rd., Farmington, CT 06032
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ABSTRACT In this paper, we report on the preparation of synthetic FeS2 and CoS2 using a relatively inexpensive aqueous process. This avoids the material and handling difficulties associated with a high-temperature approach. An aqueous approach also allows ready scale-up to a pilot-plant size facility. The FeS2 and CoS2 were characterized with respect to their physical and chemical properties. The synthetic disulfides were incorporated into catholyte mixes for testing in single cells and batteries over a range of temperatures. The results of these tests are presented and compared to the performance of natural FeS2 (pyrite) and a commercial source of CoS2. INTRODUCTION Conventional thermally activated (“thermal”) batteries employ pyrite (FeS2) as the primary cathode material with Li(Si) and Li(Al) alloys as anodes. These batteries are ideal for power sources for many military applications (e.g., missiles) because of their long shelf life. Similar technology is also being considered for potential domestic applications such as power supplies for geothermal borehole data logging. Pyrite is a relatively abundant, inexpensive naturally occurring mineral. However, before it can be used for electrochemical applications, it must be ground, sized, and then purified to remove electroactive impurities and inert gangue material. The overall processing adds greatly to the cost of the final cathode material. Synthetic pyrite has a number of advantages over natural pyrite. This material is typically nanostructured, which results in a much higher surface area and a correspondingly higher current-carrying capability. It can be easily prepared in high purity in large scale from inexpensive precursors [1-4]. This avoids much of the nonhomogeneity associated with natural pyrite from various sources. The Co analogue to pyrite, CoS2, is preferred to pyrite for applications involving high current densities, due to its much higher electronic conductivity and thermal stability (650o vs. 550oC for FeS2). It is available commercially in kg quantities from Cerac, Inc. (Butler, WI). The particle size of the natural pyrite can be controlled by selective grinding. However, no particle-size control is presently possible with the commercial CoS2. Sandia has extensively characterized such disulfides in many thermal batteries over the years and has a large database as a reference point. We studied an aqueous route for the preparation of synthetic FeS2 and CoS2 with the goal of developing a viable large-scale (e.g., 1-kg batches) process that consistently produces quality material suitable for high-temperature batteries. Some control over product particle size was also desired. This report documents the results of that study. EXPER
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