Ronald A. Guidotti

Study of Sn-Coated Graphite as Anode Material for Secondary Lithium-Ion Batteries

Tin-graphite composites have been developed as an alternate anode material for Li-ion batteries using an autocatalytic deposition technique. The specific discharge capacity, coulombic efficiency, rate capability behavior, and cycle life of Sn-C composites has been studied using a variety of electrochemical methods. The amount of tin loading and the heating temperature have a significant effect on the composite performance. The synthesis conditions and Sn loading on graphite have been optimized to obtain the maximum reversible capacity for the composite electrode. Heating the composite converts it from amorphous to crystalline form. Apart from higher capacity, Sn-graphite composites possesses higher coulombic efficiency, better rate capability, and longer cycle life than the bare synthetic graphite. Current studies are focused on reducing the first cycle irreversible capacity loss of this material.

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.

Structural and Electrochemical Characterization of Glassy Carbon Prepared from Silicon‐Doped Polymethacrylonitrile/Divinylbenzene Copolymer

There has been a great deal of discussion on the potential role of heteroatoms in carbons intended for lithium ion intercalation. Previous observations have been mixed, ranging from beneficial to detrimental effects on intercalation capacity, irreversible losses, and charge efficiencies. The introduction or substitution of silicon into a carbon matrix prepared by chemical vapor deposition has demonstrated a positive effect. The present study concerns substitutional effects in disordered carbons synthesized from polymer precursors. Solid‐state nuclear magnetic resonance, photoacoustic IR spectroscopy, X‐ray fluorescence, and high‐resolution transmission electron microscopy were used to follow the modified carbon synthesis. Silicon is successfully incorporated into the polymer matrix by copolymerizing the precursors with tetravinylsilane. On oxidative stabilization and pyrolysis, however, the Si‐C connectivity is replaced by Si‐O coordination. These silicon species appear to be discrete, and no evidence for either a crystalline or amorphous secondary phase is seen. These silicon species have a profound effect on the electrochemical performance. Irreversible loss processes are greatly increased, and charge efficiencies are decreased when compared to nonsubstituted controls.

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.

Electrochemical and spectroscopic evaluation of lithium intercalation in tailored polymethacrylonitrile carbons

Disordered polymethacrylonitrile (PMAN) carbon monoliths have been studied as potential tailored electrodes for lithium ion batteries. A combination of electrochemical and surface spectroscopic probes have been used to investigate irreversible loss mechanisms. Voltammetric measurements show that Li intercalates readily into the carbon at potentials 1V positive of the reversible Li potential. The coulometric efficiency rises rapidly from 50% for the first potential cycle to greater than 85% for the third cycle, indicating that solvent decomposition is a self-limiting process. Surface film composition and thickness, as measured by x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS), does not vary substantially when compared to more ordered carbon surfaces. Li{sup +} profiles are particularly useful in discriminating between the bound states of Li at the surface of solution permeable PMAN carbons.

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.

High-temperature batteries for geothermal and oil/gas borehole applications

A literature survey and technical evaluation was carried out of past and present battery technologies with the goal of identifying appropriate candidates for use in geothermal borehole and, to a lesser extent, oil/gas boreholes. The various constraints that are posed by such an environment are discussed. The promise as well as the limitations of various candidate technologies are presented. Data for limited testing of a number of candidate systems are presented and the areas for additional future work are detailed. The use of low-temperature molten salts shows the most promise for such applications and includes those that are liquid at room temperature. The greatest challenges are to develop an appropriate electrochemical couple that is kinetically stable with the most promising electrolytes-both organic as well as inorganic-over the wide operating window that spans both borehole environments.

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.