Frederick W. Reinhardt

Characterization of Fe/KClO4 Heat Powders and Pellets

Pellets of Fe/KClO4 mixtures are used as a heat source for thermally activated (“thermal”) batteries. They provide the energy necessary for melting the electrolyte and bringing the battery stack to operating temperature. The effects of morphology of the Fe and the heat-pellet density and composition on both the physical properties (flowability, pelletization, and pellet strength) and the pyrotechnic performance (burn rate and ignition sensitivity) were examined using several commercial sources of Fe.

Phase diagrams for the binary systems CaCl2-KCl and CaCl2-CaCrO4

Abstract Phase diagrams have been determined using differential thermal analysis for the binary systems CaCl 2 -KCl and CaCl 2 -CaCrO 4 . CaCl 2 -KCl phase diagrams have been previously reported but results were not consistent. No prior studies have been reported for the CaCl 2 -CaCrO 4 system. In the CaCl 2 -KCl binary system two eutectics have been located at 24.0 mole % KCl (m.p. 615°C) and 74.3 mole % KCl (m.p. 594°C). A double salt of composition CaKCl3 melting congruently at 741°C has been found. The CaCl 2 -CaCrO 4 system is a simple eutectic system with the eutectic occurring at 23.4 mole % CaCrO 4 and melting at 660°C.

Preparation and Characterization of Nanostructured FeS 2 and CoS 2 for High-Temperature Batteries

In this paper, we report on the preparation of synthetic FeS 2 and CoS 2 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 FeS 2 and CoS 2 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 FeS 2 (pyrite) and a commercial source of CoS 2 .

Novel Design and Fabrication of Thermal Battery Cathodes Using Thermal Spray

Li-Alloy/FeS 2 thermal batteries are the predominant thermal battery chemistry today. Conventional electrodes are fabricated by cold pressing of powders. A better means of providing thin electrodes would dramatically increase volumetric and gravimetric energy densities and cost efficiency of thermal batteries. In this study, experiments were conducted on fabricating the cathode via high-velocity oxygen-fuel (HVOF) and dc-arc plasma thermal spray technique. The deposited films were characterized by cross-section examination using Scanning Electron Microscopy (SEM) and X-ray Diffraction. The thermal decomposition of pyrite was suppressed by a proprietary additive. The electrochemical test results showed that pyrite cathodes prepared by dc-arc plasma spraying with additives demonstrated better performance compared traditional pressed-powder electrodes.

Thermal decomposition of zinc chromates

Abstract A study of the thermal decomposition in air of zinc chromates from several sources was conducted using thermogravimetry, chemical analysis, emission spectroscopy and X-ray diffraction analysis. Four zinc chromate samples were obtained from commercial suppliers and four others were prepared in this laboratory. The zinc chromates were identified as various materials depending on the method of preparation. Compounds either identified or postulated included 4ZnCrO4·K2O ·3H2O(I), 2ZnO  CrO3  H2(II), 4ZnO  CrO3·3H2O(III). ZnCrO4(IV), 5ZnO  5CrO3·Na2O  3H20(V) and 5ZnO·4CrQ3  Na2O·5H20(VI). Upon heating to 9OO°C, compound I underwent a four step decomposition to form ZnO, ZnCr2O4 and K2CrO4. Compounds II and III each decomposed in two steps to form ZnO and ZnCr2O4. The thermogram for compound IV showed only a single step with the final products also being ZnO and ZnCr2O4. The decomposition of compounds V and VI each involved two steps with the formation of ZnO, ZnCr2O4 and Na2CrO4. Chemical analyses gave assay values for the zinc chromates ranging from 40.2 to 96.9% ZnCrO4.

Thermal-sprayed, thin-film pyrite cathodes for thermal batteries-discharge-rate and temperature studies in single cells

Using an optimized thermal-spray process, coherent, dense deposits of pyrite (FeS/sub 2/) with good adhesion were formed on 304 stainless steel substrates (current collectors). After leaching with CS/sub 2/ to remove residual free sulfur, these served as cathodes in Li(Si)/FeS/sub 2/ thermal cells. The cells were tested over a temperature range of 450/spl deg/C to 550/spl deg/C under baseline loads of 125 and 250 mA/cm/sup 2/, to simulate conditions found in a thermal battery. Cells built with such cathodes outperformed standard cells made with pressed-powder parts. They showed lower interfacial resistance and polarization throughout discharge, with higher capacities per mass of pyrite. Post-treatment of the cathodes with Li/sub 2/O coatings at levels of >7% by weight of the pyrite was found to eliminate the voltage transient normally observed for these materials. Results equivalent to those of standard lithiated catholytes were obtained in this manner. The use of plasma-sprayed cathodes allows the use of much thinner cells for thermal batteries since only enough material needs to be deposited as the capacity requirements of a given application demand.

Advanced development issues related to plasma-sprayed pyrite electrodes for thermal batteries

The use of LiCI-KCl eutectic electrolyte as a co-spray additive for the plasma spraying of pyrite electrodes for thermal batteries has been demonstrated to provide greater mechanical strength and superior electrochemical performance relative to the use of elemental sulfur. However, higher electrolyte contents in the deposit relative to that of the feedstock are of concern, in that this results in lower energy densities and specific energies. A systematic study of the effect of the electrolyte concentration in the feedstock on the final physical and chemical properties of the final plasm-sprayed deposit was undertaken. The resulting deposits were then tested in single cells to characterize the resultant electrochemical properties. A study was also initiated to examine the effects of various lithiation agents at several concentrations on the initial voltage spike that occurs at the onset of discharge of such electrodes in Li(Si)/LiCl-KCl-(MgO)/FeS/sub 2/ single cells. The main technical issues that need to be resolved to make this a commercially viable processing technique are described.

Evaluation of the Li(Si)/FeS(2) and Li(Si)/CoS(2) Couples for a High-Voltage, High-Power Thermal Battery

A detailed evaluation of the Li(Si)/FeSz and Li(Si)/CoSz couples was undertaken to determine which was better suited for use in a thermal battery with challenging high-voltage and highpower requirements. The battery was to produce a minimum voltage of 205 V during pulses of 36 A superimposed on a 6-A background load. The final design called for two 96-cell batteries in series, with each providing 1.1 kW background load, with peak power levels of 6.7 kW. The battery lifetime was to be 5 min. Since it was not possible to duplicate the desired complex waveform exactly, an alternate approximating constant-current load profile was used. Single-cell tests were carried out at temperatures of 400°C – 5500C using the standard LiC1-KCl eutectic, the low-melting LiBr-KBr-LiF eutectic, and the all-lithium LiC1-LiBr-LiF minimummelting electrolyte. These screening studies were then extended to 10-cell and 25-cell batteries at the same equivalent load conditions. Both 1.25’’-dia. and 2.25’’-dia. stacks were tested. Based on these tests, the best overall results were obtained using the all-Li electrolyte with the COS2 cathode and flooded anodes. The next best electrolyte was the low-melting electrolyte. A preliminary test with a 95-cell battery showed better performance than what was expected based on results of 10and 25-cell tests, due to lower cell resistance.

Characterization of the Li(Si)/CoS(2) couple for a high-voltage, high-power thermal battery

In order to determined the capabilities of a thermal battery with high-voltage and high-power requirements, a detailed characterization of the candidate LiSi/LiCl-LiBr-LiF/CoS{sub 2} electrochemical couple was conducted. The rate capability of this system was investigated using 0.75 inch-dia. and 1.25 inch-dia. single and multiple cells under isothermal conditions, where the cells were regularly pulsed at increasingly higher currents. Limitations of the electronic loads and power supplies necessitated using batteries to obtain the desired maximum current densities possible for this system. Both 1.25 inch-dia. and 3 inch-dia. stacks were used with the number of cells ranging from 5 to 20. Initial tests involved 1.25 inch-dia. cells, where current densities in excess of 15 A/cm{sup 2} (>200 W/cm{sup 2}) were attained with 20-cell batteries during 1-s pulses. In subsequent follow-up tests with 3 inch-dia., 10-cell batteries, ten 400-A 1-s pulses were delivered over an operating period often minutes. These tests formed the foundation for subsequent full-sized battery tests with 125 cells with this chemistry.

Evaluation of Aerogel Materials for High-Temperature Batteries

Siiica aerogels have 1/3 the thermal conductivity of the best commercial composite insulations, or ~13 mW/m-K at 25°C. However, aerogels are transparent in the near IR region of 4-7 µm, which is where the radiation peak from a thermal-battery stack occurs. Titania and carbon- black powders were examined as thermal opacifiers, to reduce radiation at temperatures between 300°C and 600°C, which spans the range of operating temperature for most thermal batteries. The effectiveness of the various opacifiers depended on the loading, with the best overall results being obtained using aerogels filled with carbon black. Fabrication and strength issues still remain, however.