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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Solid State Electrolytes Prepared from PEO (360) Silanated Silica

All solid state composite electrolytes were prepared using fumed silica (SiO2) silanated with an oligomeric polyethylene oxide (PEO) silane containing 6-9 ethylene oxide repeat units, a PEO matrix and LiClO4 (8/1 O/Li). The PEO-silane covalently attached to the silica was amorphous, with a T(sub g) that increased from -90 C to -53 C after attachment. The conductivity of films prepared using the PEO-silanated silica increased to approx. 6 x 10(exp -5) S/cm at RT compared with approx. 1 x 10(-5) S/cm for films prepared with unsilanated SiO2.

Maitra, P.↗
NASA NTRS2002

Inter and Intra Molecular Phase Separation Environment Effects on PI-PEO Block Copolymers for Batteries and Fuel Cells

Rod-coil molecules have been introduced as a novel type of block copolymers with unique microstructure due to their ability to self-assemble to various ordered morphologies on a nanometer length scale. These molecules, comprised two homo polymers joined together at one end, microphase separate into ordered, periodic arrays of spheres, cylinders in the bulk state and or solution. To get ordered structure in a reasonable scale, additional force field are applied, such as mechanical shearing, electric field and magnetic field. Recently, progress has made it a possible to develop a new class of polyimides (PI)-Polyethylene oxide (PEO) that are soluble in polar organic solvents. The solvent-soluble PI-PEO has a wide variety of applications in microelectronics, since these PI-PEO films exhibit a high degree of thermal and chemical stability. In this paper, we report the self-assembled ordered structure of PI-PEO molecules formed from concentrate solution.

Xue, Chen-Chen↗
NASA NTRSDate not supplied

Manufacturing, Characterization and Terrestrial Passive Radiative Cooling Performance of Nanofibrous PTFR-PEO Composite Thermal Coatings

Passive heat management is desirable in many applications since it can reduce the energy expended for cooling, for example, in buildings and automobiles. Specifically, materials with wavelength-dependent reflectance and emittance can manage incident solar fluxes while enabling passive radiative cooling by thermal emission. This study demonstrates the use of polymeric nanofibers, specifically polytetrafluoroethylene (PTFE) and polyethylene oxide (PEO) composite, as thermal coatings for passive temperature control. Employing the electrospinning fabrication process, we engineer nano and micro-scale fibrous structures, studying the influence of fabrication parameters, such as precursor material concentration and rotating collector speed, on fiber geometry and optical properties. To understand the role of material and fiber geometry on optical performance, we characterize various samples' spectral reflectance, absorptance, and transmittance using spectrophotometers interfaced with integrating spheres. The results show the potential of nanofabricated PTFE-PEO coatings as promising candidates for passive thermal control. We highlight their competitive edge by comparing their solar reflectance and emittance values to existing passive radiative thermal control materials. In essence, this study contributes to advancing passive heat management technologies, offering insights into optimizing material composition and fabrication techniques for enhanced performance in various applications.

Chieloka Ibekwe↗
NASA NTRS2005

Homopolyrotaxanes and Homopolyrotaxane Networks of PEO

In order to identify the optimum size of macrocrown ether for threading, we first investigated the size and shape of simple crown ethers in the melt at 373 K, and their extent of threading with PEO in the melt using coarse-grained Monte Carlo simulations on the 2nnd (second nearest neighbor diamond) lattice, which is a high coordination lattice whose coarse-grained chains can be reverse mapped into fully atomistic models in continuous space.

Pugh, Coleen↗
NASA NTRS2024

Plasma Rapid Oxidation Technique for Extending Component Tenability (PROTECT)

Additive manufacturing (AM) is increasingly utilized in aerospace applications. However, post-processing is required for many applications, so intricate designs are limited. Plasma electrolytic oxidation (PEO) was investigated as a post-processing treatment on Ti-6-4 (or Ti-6Al-4V: Alpha-beta titanium alloy with a high specific strength and excellent corrosion resistance)additively manufactured specimens. The “Keronite Black” PEO treatment reduced the surface roughness (Ra) of test specimens by approximately 0.5 μm. This reduction in Ra compared to the as-printed sample was hypothesized to benefit corrosion and fatigue properties because increased Ra is known to negatively impact corrosion and fatigue characteristics. Up to a 101% improvement in the corrosion potential (Ɛcorr) was observed. Although fatigue characteristics varied by PEO parameters, there was no significant fatigue debit due to the PEO treatment. Additionally, no effect to adhesion characteristics was observed due to PEO treatment. It is recommended that additional studies investigate the ability of PEO treatments to improve the corrosion, fatigue, chemical compatibility, radiation hardening, particle shedding characteristics, and flammability/oxidizer compatibility of aerospace additively manufactured components.

Jennifer Williams↗
NASA NTRS1992

Effects of 12-crown-4 ether on the electrochemical performance of CoO2 and TiS2 cathodes in Li polymer electrolyte cells

The effect of adding 12-crown-4 ether (12Cr4) to the polyethylene oxide (PEO) electrolyte on the electrochemical properties of cells with Li(x)CoO2 or TiS2 as the cathode was investigated. The polymer electrolyte films were: (1) PEO, LiBF4; (2) PEO, LiBF4 with 12Cr4; (3) Li(x)CoO2, PEO, and LiBF4; and (4) Li(x)CoO2, PEO, LiBF4, and 12Cr4. It was found that, although 12Cr4 improved the cell performance over cells without 12Cr4 in the shallow c/d cycles (cyclic voltammetric behavior), it did not seem to prolong the active life of the cell. The cells with CoO2 as the cathode failed after a few c/d cycles, while similar cells with TiS2 did not fail even after 12 c/d cycles. The probable cause of failure in the case of CoO2 is ascribed to the instability of the CoO2 cathode.

Nagasubramanian, G.↗
NASA NTRS2005

Novel Elastomeric Membranes Developed for Polymer Electrolytes in Lithium Batteries

Lithium-based polymer batteries for aerospace applications need to be highly conductive from -70 to 70 C. State-of-the-art polymer electrolytes are based on polyethylene oxide (PEO) because of the ability of its ether linkages to solvate lithium ions. Unfortunately, PEO has a tendency to form crystalline regions below 60 C, dramatically lowering conductivity below this temperature. PEO has acceptable ionic conductivities (10(exp -4) to 10(exp -3) S/cm) above 60 C, but it is not mechanically strong. The room-temperature conductivity of PEO can be increased by adding solvent or plasticizers, but this comes at the expense of thermal and mechanical stability. One of NASA Glenn Research Center s objectives in the Polymer Rechargeable System program (PERS) is to develop novel polymer electrolytes that are highly conductive at and below room temperature without added solvents or plasticizers.

Tigelaar, Dean M.↗
NASA NTRS1993

Composite Solid Electrolyte for Li Battery Applications

The electrochemical, bulk and interfacial properties of the polyethylene oxide (PEO) based composite solid electrolyte (CSE) comprising LiI, PEO, and Al2O3 have been evaluated for Li battery applications. The bulk interfacial and transport properties of the CSEs seem to strongly depend on the alumina particle size. For the CSE films with 0.05 micron alumina while the bulk conductivity is around 10(exp -4) (mho/cm) at 103 C, the Li ion transport number seems to be close to unity at the same temperature. Compared to the PEO electrolyte this polymer composite electrolyte seems to exhibit robust mechanical and interfacial properties. We have studied three different films with three different alumina sizes in the range 0.01-0.3 micron. Effects of Al2O3 particle size on the electrochemical performance of polymer composite electrolyte is discussed. With TiS2 as cathode a 10 mAh small capacity cell was charged and discharged at C/40 and C/20 rates respectively.

Nagasubramanian, G.↗
NASA NTRS2005

New Aptes Cross-linked Polymers from Poly(ethylene oxide)s and Cyanuric Chloride for Lithium Batteries

A new series of polymer electrolytes for use as membranes for lithium batteries are described. Electrolytes were made by polymerization between cyanuric chloride and diamino-terminated poly(ethylene oxide)s, followed by cross-linking via a sol-gel process. Thermal analysis and lithium conductivity of freestanding polymer films were studied. The effects of several variables on conductivity were investigated, such as length of backbone PEO chain, length of branching PEO chain, extent of branching, extent of cross-linking, salt content, and salt counterion. Polymer films with the highest percentage of PEO were found to be the most conductive, with a maximum lithium conductivity of 3.9 x 10(exp -5) S/cm at 25 C. Addition of plasticizer to the dry polymers increased conductivity by an order of magnitude.

Tigelaar, Dean M.↗
NASA NTRS2007

Composite Electrolytes for Lithium Batteries: Ionic Liquids in APTES Crosslinked Polymers

Solvent free polymer electrolytes were made consisting of Li(+) and pyrrolidinium salts of trifluoromethanesulfonimide added to a series of hyperbranched poly(ethylene oxide)s (PEO). The polymers were connected by triazine linkages and crosslinked by a sol-gel process to provide mechanical strength. The connecting PEO groups were varied to help understand the effects of polymer structure on electrolyte conductivity in the presence of ionic liquids. Polymers were also made that contain poly(dimethylsiloxane) groups, which provide increased flexibility without interacting with lithium ions. When large amounts of ionic liquid are added, there is little dependence of conductivity on the polymer structure. However, when smaller amounts of ionic liquid are added, the inherent conductivity of the polymer becomes a factor. These electrolytes are more conductive than those made with high molecular weight PEO imbibed with ionic liquids at ambient temperatures, due to the amorphous nature of the polymer.

Tigelaar, Dean M.↗
NASA NTRS1992

Secondary Li battery incorporating 12-Crown-4 ether

A rechargeable lithium battery which utilizes a polyethylene oxide (PEO) solid polymeric electrolyte complexed with a lithium salt is disclosed. The conductivity is increased an order of magnitude and interfacial charge transfer resistance is substantially decreased by incorporating a minor amount of 12-Crown-4 ether in the PEO-lithium salt solid electrolyte film. Batteries containing the improved electrolyte permit operation at a lower temperature with improved efficiency.

Nagasubramanian, Ganesan↗
NASA NTRS2002

Preparation and Characterization of Single Ion Conductors from High Surface Area Fumed Silica

Anions that can form dissociative salts with Li(+) have been prepared and covalently attached to high surface area fumed silica. When blended with polyethylene oxide (PEO), the functionalized fumed silica suppresses the crystallization of the PEO, provides dimensional stability, and serves as a single ion conductor. Since functionalized fumed silica is easily dispersed in common polar solvents, it can be incorporated in both the polymer electrolyte and the electrodes.

Zhang, H.↗
NASA NTRS2004

Preparation of Proton Exchange Membranes and Lithium Batteries from Melamine-containing Ormosils

Our laboratory has recently reported a series of rodcoil polymers for lithium batteries that display dimensionally stable films with good ionic conductivity. The rod segments consist of rigid linear and branched polyimides and the coil segments are polyethylene oxides (PEO). It has been proposed that good mechanical and transport properties are due to phase separation between the rod and coil segments. It was also observed that increased branching and molecular weight lead to increased conductivity. The following study was undertaken to assess the effects of phase separation in polyalkylene oxides connected by melamine linkages. Melamine was chosen as the linking unit because it provides a branching site, cation binding sites to help ionic transport between polymer chains, and the opportunity for self assembly through hydrogen bonding. Polymers were made by the reaction of cyanuric chloride with a series of amine-terminated alkylene oxides. A linear polymer was first made, followed by reaction of the third site on cyanuric chloride with varying ratios of monofunctional Jeffamine and (3-aminopropyl)triethoxysilane. The lithium trifluoromethane sulfonamide-doped polymers are then crosslinked through a sol-gel process to form free-standing films. Initial results have shown mechanically strong films with lithium conductivities on the order of 2 x 10(exp -5) S/cm at ambient temperature. In a separate study, organically modified silanes (Ormosils) that contain sulfonic acid derivatized melamines have been incorporated into proton exchange membranes. The membranes are made by reaction of the primary amine groups of various ratios of melamine derivative and difunctional Jeffamine (MW = 2000) with the epoxide group of (3-Glycidyloxypropyl)trimethoxysilane. The films were then cross-linked through a sol-gel process. Resulting sulfuric acid doped films are strong, flexible, and have proton conductivities on the order of 2 x l0(exp -2) S/cm (120 C, 25% relative humidity). Our best results have been observed when films contain 60% PEO and 40% sulfonated melamine.

Tigelaar, Dean M.↗
NASA NTRS2007

Use of Ionic Liquids in Rod-Coil Block Copolyimides for Improved Lithium Ion Conduction

Solvent-free, solid polymer electrolytes (SPE) have the potential to improve safety, increase design flexibility and enhance performance of rechargeable lithium batteries. Solution based electrolytes are flammable and typically incompatible with lithium metal anodes, limiting energy density. We have previously demonstrated use of polyimide rod coil block copolymers doped with lithium salts as electrolytes for lithium polymer batteries. The polyimide rod blocks provide dimensional stability while the polyethylene oxide (PEO) coil portions conduct ions. Phase separation of the rods and coils in these highly branched polymers provide channels with an order of magnitude improvement in lithium conduction over polyethylene oxide itself at room temperature. In addition, the polymers have been demonstrated in coin cells to be compatible with lithium metal. For practical use at room temperature and below, however, at least an order of magnitude improvement in ion conduction is still required. The addition of nonvolatile, room temperature ionic liquids has been shown to improve the ionic conductivity of high molecular weight PEO. Herein we describe use of these molten salts to improve ionic conductivity in the rod-coil block copolymers.

Meador, Mary Ann B.↗
NASA NTRS2009

Room-Temperature-Cured Copolymers for Lithium Battery Gel Electrolytes

Polyimide-PEO copolymers (PEO signifies polyethylene oxide) that have branched rod-coil molecular structures and that can be cured into film form at room temperature have been invented for use as gel electrolytes for lithium-ion electric-power cells. These copolymers offer an alternative to previously patented branched rod-coil polyimides that have been considered for use as polymer electrolytes and that must be cured at a temperature of 200 C. In order to obtain sufficient conductivity for lithium ions in practical applications at and below room temperature, it is necessary to imbibe such a polymer with a suitable carbonate solvent or ionic liquid, but the high-temperature cure makes it impossible to incorporate and retain such a liquid within the polymer molecular framework. By eliminating the high-temperature cure, the present invention makes it possible to incorporate the required liquid.

Meador, Mary Ann B.↗
NASA NTRS2006

Composite Solid Electrolyte Containing Li+- Conducting Fibers

Improved composite solid polymer electrolytes (CSPEs) are being developed for use in lithium-ion power cells. The matrix components of these composites, like those of some prior CSPEs, are high-molecular-weight dielectric polymers [generally based on polyethylene oxide (PEO)]. The filler components of these composites are continuous, highly-Li(+)-conductive, inorganic fibers. PEO-based polymers alone would be suitable for use as solid electrolytes, were it not for the fact that their room-temperature Li(+)-ion conductivities lie in the range between 10(exp -6) and 10(exp -8) S/cm, too low for practical applications. In a prior approach to formulating a CSPE, one utilizes nonconductive nanoscale inorganic filler particles to increase the interfacial stability of the conductive phase. The filler particles also trap some electrolyte impurities. The achievable increase in conductivity is limited by the nonconductive nature of the filler particles.

Appleby, A. John↗
NASA NTRS2003

Rod/Coil Block Copolyimides for Ion-Conducting Membranes

Rod/coil block copolyimides that exhibit high levels of ionic conduction can be made into diverse products, including dimensionally stable solid electrolyte membranes that function well over wide temperature ranges in fuel cells and in lithium-ion electrochemical cells. These rod/coil block copolyimides were invented to overcome the limitations of polymers now used to make such membranes. They could also be useful in other electrochemical and perhaps some optical applications, as described below. The membranes of amorphous polyethylene oxide (PEO) now used in lithium-ion cells have acceptably large ionic conductivities only at temperatures above 60 C, precluding use in what would otherwise be many potential applications at lower temperatures. PEO is difficult to process, and, except at the highest molecular weights it is not very dimensionally stable. It would be desirable to operate fuel cells at temperatures above 80 C to take advantage of better kinetics of redox reactions and to reduce contamination of catalysts. Unfortunately, proton-conduction performance of a typical perfluorosulfonic polymer membrane now used as a solid electrolyte in a fuel cell decreases with increasing temperature above 80 C because of loss of water from within the membrane. The loss of water has been attributed to the hydrophobic nature of the polymer backbone. In addition, perfluorosulfonic polymers are expensive and are not sufficiently stable for long-term use. Rod/coil block copolyimides are so named because each molecule of such a polymer comprises short polyimide rod segments alternating with flexible polyether coil segments (see figure). The rods and coils can be linear, branched, or mixtures of linear and branched. A unique feature of these polymers is that the rods and coils are highly incompatible, giving rise to a phase separation with a high degree of ordering that creates nanoscale channels in which ions can travel freely. The conduction of ions can occur in the coil phase, the rod phase, or both phases.

Meador, Mary Ann B.↗