Electrochemical studies in non-aqueous solvents. I - Acetonitrile
Electrochemical studies in nonaqueous nitrile solvent acetonitrile
ACETONITRILE↗
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Mixed solvent electrolytes for ambient temperature secondary lithium cells
The present invention comprises an improved electrolyte for secondary lithium-based cells as well as batteries fabricated using this electrolyte. The electrolyte is a lithium containing salt dissolved in a non-aqueous solvent, which is made from a mixture of ethylene carbonate, ethylene propylene diene terpolymer, 2-methylfuran, and 2-methyltetrahydrofuran. This improved, mixed solvent electrolyte is more conductive than prior electrolytes and much less corrosive to lithium anodes. Batteries constructed with this improved electrolyte utilize lithium or lithium alloy anodes and cathodes made of metal chalcogenides or oxides, such as TiS.sub.2, NbSe.sub.3, V.sub.6 O.sub.13, V.sub.2 O.sub.5, MoS.sub.2, MoS.sub.3, CoO.sub.2, or CrO.sub.2, dissolved in a supporting polymer matrix, like EPDM. The preferred non-aqueous solvent mixture comprises approximately 5 to 30 volume percent ethylene carbonate, approximately 0.01 to 0.1 weight percent ethylene propylene diene terpolymer, and approximately 0.2 to 2 percent 2-methylfuran, with the balance being 2-methyltetrahydrofuran. The most preferred solvent comprises approximately 10 to 20 volume percent ethylene carbonate, about 0.05 weight percent ethylene propylene diene terpolymer, and about 1.0 percent 2-methylfuran, with the balance being 2-methyltetrahydrofuran. The concentration of lithium arsenic hexafluoride can range from about 1.0 to 1.8 M; a concentration 1.5 M is most preferred. Secondary batteries made with the improved electrolyte of this invention have lower internal impedance, longer cycle life, higher energy density, low self-discharge, and longer shelf life.
Shen, David H.↗
Non-aqueous cleaning solvent substitution
A variety of environmental, safety, and health concerns exist over use of chlorinated and fluorinated cleaning solvents. Sandia National Laboratories, Lawrence Livermore National Laboratories, and the Kansas City Division of AlliedSignal have combined efforts to focus on finding alternative cleaning solvents and processes which are effective, environmentally safe, and compliant with local, state, and federal regulations. An alternative solvent has been identified, qualified, and implemented into production of complex electronic assemblies, where aqueous and semi-aqueous cleaning processes are not allowed. Extensive compatibility studies were performed with components, piece-parts, and materials. Electrical testing and accelerated aging were used to screen for detrimental, long-term effects. A terpene, d-limonene, was selected as the solvent of choice, and it was found to be compatible with the components and materials tested. A brief history of the overall project will be presented, along with representative cleaning efficiency results, compatibility results, and residual solvent data. The electronics industry is constantly searching for proven methods and environmentally-safe materials to use in manufacturing processes. The information in this presentation will provide another option to consider on future projects for applications requiring high levels of quality, reliability, and cleanliness from non-aqueous cleaning processes.
Meier, Gerald J.↗
Additive for Low-Temperature Operation of Li-(CF)n Cells
Some progress has been reported in continuing research on the use of anion-receptor compounds as electrolyte additives to increase the sustainable rates of discharge and, hence, the discharge capacities, of lithium-poly(carbon monofluoride) [Li-(CF)n, where n >1] primary electrochemical power cells. Some results of this research at a prior stage were summarized in Increasing Discharge Capacities of Li(CF)n Cells (NPO-42346), NASA Tech Briefs, Vol. 32, No. 2 (February 2008), page 37. A major difference between the present and previously reported results is that now there is some additional focus on improving performance at temperatures from ambient down to as low as 40 C. To recapitulate from the cited prior article: During the discharge of a Li-(CF)n cell, one of the electrochemical reactions causes LiF to precipitate at the cathode. LiF is almost completely insoluble in most non-aqueous solvents, including those used in the electrolyte solutions of Li- (CF)n cells. LiF is electrochemically inactive and can block the desired transport of electrons at the cathode, and, hence, the precipitation of LiF can form an ever-thickening film on the cathode that limits the rate of discharge. An anion-receptor electrolyte additive helps to increase the discharge capacity in two ways: It renders LiF somewhat soluble in the non-aqueous electrolyte solution, thereby delaying precipitation until a high concentration of LiF in solution has been reached. When precipitation occurs, it promotes the formation of large LiF grains that do not conformally coat the cathode. The net effect is to reduce the blockage caused by precipitation of LiF, thereby maintaining a greater degree of access of electrolyte to the cathode and greater electronic conductivity.
West, William↗
Corrosion of metals by hydrazine
The mechanism of corrosion of metals by hydrazine has been studied by means of coupons in sealed ampoules and by electrochemical techniques. The variables considered were temperature, CO2 impurity level, alloy composition and microcrystalline structure. The coupon studies, to date, verify that increasng temperature and the presence of CO2 does increase the corrosion rate as expected. The presence of molybdenum in stainless steels to the 3 percent level is not necessarily deleterious, contrary to published reports. The influence of microcrystalline structure and surface characteristics are more dominant effects. However, with Ti-6Al-4V, two different microcrystalline structures showed no significant differences. Corrosion rates of CRES 304 L in hydrazine have also been measured by several electrochemical techniques such as Tafel plots, polarization resistance and A. C. Impedance. This is the first documented work to show that A. C. Impedance can be used with non-aqueous solvents. Preliminary data correlated satisfactorily with the results of the coupon studies.
Lawton, E. A.↗
Microcapsules and Methods for Making
Methods of forming multi-lamellar microcapsules having alternating layers of hydrophilic and hydrophobic immiscible liquid phases have been developed using different polymer/solvent systems. The methods use liquid-liquid diffusion and simultaneous lateral phase separation, controlled by proper timed-sequence exposures of immiscible phases and low shear mixing, to form narrow size distributions of spherical, multilamellar microcapsules. The use of special formulations of solubilized drugs, surfactants, and polymeric co-surfactants in aqueous vehicles which are dispersed in hydrocarbon solvents containing small quantities of oil, low molecular weight co-surfactants and glycerides that are aqueous insoluble enables the formation of unique microcapsules which can carry large amounts of pharmaceuticals in both aqueous and non-aqueous solvent compartments. The liquid microcapsules are quickly formed in a single step and can include a polymeric outer 'skin' which protects the microcapsules during physical manipulation or exposure to high shear forces. Water-in-oil and oil-in-water microcapsules have been formed both in 1 x g and in microgravity, which contain several types of drugs co-encapsulated within different fluid compartments inside the same microcapsule. Large, spherical multi-lamellar microcapsules have been formed including a cytotoxic drug co-encapsulated with a radiocontrast medium which has advantages for chemoembolization of vascular tumors. In certain cases, crystals of the drug form inside the microcapsules providing zero-order and first order, sustained drug release kinetics.
Morrison, Dennis R.↗
Increasing Discharge Capacities of Li-(CF)(sub n) Cells
An electrolyte additive has shown promise as a means of increasing the sustainable rates of discharge and, hence, the discharge capacities, of lithiumpoly(carbon monofluoride) electrochemical power cells. Lithium-poly(carbon monofluoride) [Li-(CF)n] cells and batteries offer very high specific energies practical values of about 600 W.h/g and a theoretical maximum value of 2,180 W.h/kg. However, because Li-(CF)n cells and batteries cannot withstand discharge at high rates, they have been relegated to niche applications that involve very low discharge currents over times of the order of hundreds to thousands of hours. Increasing the discharge capacities of Li- (CF)n batteries while maintaining high practical levels of specific energy would open new applications for these batteries. During the discharge of a Li-(CF)n cell, one of the electrochemical reactions causes LiF to precipitate at the cathode. LiF is almost completely insoluble in most non-aqueous solvents, including those used in the electrolyte solutions of Li-(CF)n cells. LiF is electrochemically inactive and can block the desired transport of ions at the cathode, and, hence, the precipitation of LiF can form an ever-thickening film on the cathode that limits the rate of discharge.
Whitacre, Jay↗
ExCALiBR: An Instrument for Uncovering the Origin of the Moon’s Organics.
Lipids are organic molecules of great astrobiological interest for future NASA missions to the Moon, Mars and Icy Worlds. Lipids are essential for life as we know it, and likely also required for putative extraterrestrial organisms. These robust organics can be synthesized abiotically and survive for long periods of geological time. Laboratory characterization techniques are well established but are laborious, operator dependent, and require large volumes of consumables, precluding in situ analysis. We are developing an autonomous, miniaturized fluidic system, integrating lab techniques for lipid analysis while minimizing rea-gent volumes and concentrating organics for analysis, thereby increasing signal-to-noise ratios by orders of magnitude. This system, the Extractor for Chemical Analysis of Lipid Biomarkers in Regolith (ExCALiBR), will enable future organic surveys by extracting and concentrating lipids from approximately 50 grams of regolith using a fluidic and microfluidic sample processor made of materials compatible with non-aqueous solvents required for extraction. ExCAL-iBR can be deployed on a lander or used on a crewed mission.
M B Wilhelm↗
Solutions Remediate Contaminated Groundwater
During the Apollo Program, NASA workers used chlorinated solvents to clean rocket engine components at launch sites. These solvents, known as dense non-aqueous phase liquids, had contaminated launch facilities to the point of near-irreparability. Dr. Jacqueline Quinn and Dr. Kathleen Brooks Loftin of Kennedy Space Center partnered with researchers from the University of Central Florida's chemistry and engineering programs to develop technology capable of remediating the area without great cost or further environmental damage. They called the new invention Emulsified Zero-Valent Iron (EZVI). The groundwater remediation compound is cleaning up polluted areas all around the world and is, to date, NASA's most licensed technology.
Source record↗
Zero-Valent Metal Emulsion for Reductive Dehalogenation of DNAPLS
A zero-valent metal emulsion is used to dehalogenate solvents, such as pooled dense non-aqueous phase liquids (DNAPLs), including trichloroethylene (TCE). The zero-valent metal emulsion contains zero-valent metal particles, a surfactant, oil and water. The preferred zero-valent metal particles are nanoscale and microscale zero-valent iron particles
Debra R Reinhart↗
Zero-Valent Metal Emulsion for Reductive Dehalogenation of DNAPLs
A zero-valent metal emulsion is used to dehalogenate solvents, such as pooled dense non-aqueous phase liquids (DNAPLs), including trichloroethylene (TCE). The zero-valent metal emulsion contains zero-valent metal particles, a surfactant, oil and water, The preferred zero-valent metal particles are nanoscale and microscale zero-valent iron particles.
Reinhart, Debra R.↗
Application of Emulsified Zero-Valent Iron to Marine Environments
Contamination of marine waters and sediments with heavy metals and dense non-aqueous phase liquids (DNAPLs) including chlorinated solvents, pesticides and PCBs pose ecological and human health risks through the contaminant's potential bioaccumulation in fish, shellfish and avian populations. The contaminants enter marine environments through improper disposal techniques and storm water run-off. Current remediation technologies for application to marine environments include costly dredging and off-site treatment of the contaminated media. Emulsified zero-valent iron (EZVI) has been proven to effectively degrade dissolved-phase and DNAPL-phase contaminants in freshwater environments on both the laboratory and field-scale level. However, the application to marine environments is only just being explored. This paper discusses the potential use of EZVI in brackish and saltwater environments, with supporting laboratory data detailed. Laboratory studies were performed in 2005 to establish the effectiveness of EZVI to degrade trichloroethylene (TCE) in saltwater. Headspace vials were setup to determine the kinetic rate of TCE degradation using EZVI in seawater. The reaction vials were analyzed by Gas Chromatographic/Flame Ionization Detection (GC/FID) for ethene production after a 48 day period using a GC/FID Purge and Trap system. Analytical results showed that EZVI was very effective at degrading TCE. The reaction by-products (ethene, acetylene and ethane) were produced at 71% of the rate in seawater as in the fresh water controls. Additionally, iron within the EZVI particles was protected from oxidation of the corrosive seawater, allowing EZVI to perform in an environment where zero-valent iron alone could not compete. Laboratory studies were also performed to establish the effectiveness of emulsified zero-valent metal (EZVM) to remove dissolved-phase cadmium and lead found in seawater. EZVM is comprised of a combination of magnesium and iron metal surrounded by the same oil/surfactant membrane used in EZVI. The removal of cadmium and lead from a seawater matrix is a unique challenge. It requires a system that is resistant to the corrosive nature of seawater while removing specific ions that are in a relatively low concentration compared to naturally occurring seawater salts. Laboratory studies conducted show greater than 99% removal of lead and 96% removal of cadmium from a seawater solution spiked at 5 mg/L that was treated with an Emulsified Zero-Valent Metal (EZVM). The cadmium and lead are removed from the solution as they transport across the emulsion membrane and plate out onto the zero-valent metal surface.
Brooks, Kathleen B.↗
Application of Emulsified Zero-Valent Iron to Marine Environments
Contamination of marine waters and sediments with heavy metals and dense non-aqueous phase liquids (DNAPLs) including chlorinated solvents, pesticides and PCBs pose ecological and human health risks through the potential of the contaminant to bioaccumulate in fish, shellfish and avian populations. The contaminants enter marine environments through improper disposal techniques and storm water runoff. Current remediation technologies for application to marine environments include costly dredging and off-site treatment of the contaminated media. Emulsified zero-valent iron (EZVI) has been proven to effectively degrade dissolved-phase and DNAPL-phase contaminants in freshwater environments on both the laboratory and field-scale level. Emulsified Zero-Valent Metal (EZVM) using metals such as iron and/or magnesium have been shown in the laboratory and on the bench scale to be effective at removing metals contamination in freshwater environments. The application to marine environments, however, is only just being explored. This paper discusses. the potential use of EZVI or EZVM in brackish and saltwater environments, with supporting laboratory data detailing its effectiveness on trichloroethylene, lead, copper, nickel and cadmium.
Quinn, Jacqueline W.↗
Redox chemistry at liquid/liquid interfaces
The interface between two immiscible liquids with immobilized photosynthetic pigments can serve as the simplest model of a biological membrane convenient for the investigation of photoprocesses accompanied by spatial separation of charges. As it follows from thermodynamics, if the resolvation energies of substrates and products are very different, the interface between two immiscible liquids may act as a catalyst. Theoretical aspects of charge transfer reactions at oil/water interfaces are discussed. Conditions under which the free energy of activation of the interfacial reaction of electron transfer decreases are established. The activation energy of electron transfer depends on the charges of the reactants and dielectric permittivity of the non-aqueous phase. This can be useful when choosing a pair of immiscible solvents to decrease the activation energy of the reaction in question or to inhibit an undesired process. Experimental interfacial catalytic systems are discussed. Amphiphilic molecules such as chlorophyll or porphyrins were studied as catalysts of electron transfer reactions at the oil/water interface.
Non-NASA Center↗
Supercapacitor Electrolyte Solvents with Liquid Range Below -80 C
A previous NASA Tech Brief ["Low-Temperature Supercapacitors" (NPO-44386) NASA Tech Briefs, Vol. 32, No 7 (July 2008), page 32] detailed ongoing efforts to develop non-aqueous supercapacitor electrolytes capable of supporting operation at temperatures below commercially available cells (which are typically limited to charging and discharging at > or equal to -40 C). These electrolyte systems may enable energy storage and power delivery for systems operating in extreme environments, such as those encountered in the Polar regions on Earth or in the exploration of space. Supercapacitors using these electrolytes may also offer improved power delivery performance at moderately low temperatures (e.g. -40 to 0 C) relative to currently available cells, offering improved cold-cranking and cold-weather acceleration capabilities for electrical or hybrid vehicles. Supercapacitors store charge at the electrochemical double-layer, formed at the interface between a high surface area electrode material and a liquid electrolyte. The current approach to extending the low-temperature limit of the electrolyte focuses on using binary solvent systems comprising a high-dielectric-constant component (such as acetonitrile) in conjunction with a low-melting-point co-solvent (such as organic formates, esters, and ethers) to depress the freezing point of the system, while maintaining sufficient solubility of the salt. Recent efforts in this area have led to the identification of an electrolyte solvent formulation with a freezing point of -85.7 C, which is achieved by using a 1:1 by volume ratio of acetonitrile to 1,3-dioxolane
Brandon, Erik↗
Lithium Dinitramide as an Additive in Lithium Power Cells
Lithium dinitramide, LiN(NO2)2 has shown promise as an additive to nonaqueous electrolytes in rechargeable and non-rechargeable lithium-ion-based electrochemical power cells. Such non-aqueous electrolytes consist of lithium salts dissolved in mixtures of organic ethers, esters, carbonates, or acetals. The benefits of adding lithium dinitramide (which is also a lithium salt) include lower irreversible loss of capacity on the first charge/discharge cycle, higher cycle life, lower self-discharge, greater flexibility in selection of electrolyte solvents, and greater charge capacity. The need for a suitable electrolyte additive arises as follows: The metallic lithium in the anode of a lithium-ion-based power cell is so highly reactive that in addition to the desired main electrochemical reaction, it engages in side reactions that cause formation of resistive films and dendrites, which degrade performance as quantified in terms of charge capacity, cycle life, shelf life, first-cycle irreversible capacity loss, specific power, and specific energy. The incidence of side reactions can be reduced through the formation of a solid-electrolyte interface (SEI) a thin film that prevents direct contact between the lithium anode material and the electrolyte. Ideally, an SEI should chemically protect the anode and the electrolyte from each other while exhibiting high conductivity for lithium ions and little or no conductivity for electrons. A suitable additive can act as an SEI promoter. Heretofore, most SEI promotion was thought to derive from organic molecules in electrolyte solutions. In contrast, lithium dinitramide is inorganic. Dinitramide compounds are known as oxidizers in rocket-fuel chemistry and until now, were not known as SEI promoters in battery chemistry. Although the exact reason for the improvement afforded by the addition of lithium dinitramide is not clear, it has been hypothesized that lithium dinitramide competes with other electrolyte constituents to react with lithium on the surface of the anode to form a beneficial SEI. Apparently, nitrides and oxides that result from reduction of lithium dinitramide on the anode produce a thin, robust SEI different from the SEIs formed from organic SEI promoters. The SEI formed from lithium dinitramide is more electronically insulating than is the film formed in the presence of an otherwise identical electrolyte that does not include lithium dinitramide. SEI promotion with lithium dinitramide is useful in batteries with metallic lithium and lithium alloy anodes.
Gorkovenko, Alexander A.↗
Valiant 'Zero-Valent' Effort Restores Contaminated Grounds
Dense non-aqueous phase liquids (DNAPLs) are chemical compounds that can contaminate soil and groundwater to the point of irreparability. These substances are only slightly soluble in water, and are much denser than water. Because of their solubility, DNAPLs form separate liquid phases in groundwater, and because of their density, DNAPLs sink in aquifers instead of floating at the water table, making it extremely difficult to detect their presence. If left untreated in the ground, they can taint fresh water sources. Common DNAPLs include chlorinated hydrocarbon compounds such as carbon tetrachloride, chloroform, tetrachloroethylene, and trichloroethylene. Trichloroethylene was used during the early days of the Space Program, as a solvent for flushing rocket engines, and for metal cleaning and degreasing of equipment, electronics, and heavy machinery. As a result, areas of Cape Canaveral s Launch Complex 34, the site of several historic Saturn rocket launches occurring from 1959 to 1968, were polluted with chlorinated DNAPLs. Through the direction and guidance of Dr. Jacqueline Quinn, an environmental engineer in the Spaceport Engineering and Technology Directorate at NASA s Kennedy Space Center, a biodegradable environmental cleanup technology was developed to reductively dechlorinate DNAPL sources in polluted water at Launch Complex 34. It was important for Kennedy to nip this problem in the bud, in light of the fact that the Space Center is also a National Wildlife Refuge, home to thousands of shorebirds, endangered sea turtles and eagles, manatees, alligators, and diverse habitats that include brackish marshes and salt water estuaries. The success in remediating this historic launch site has led to numerous commercial applications that are restoring the health of our environmental surroundings.
Source record↗