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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Computational Predictions of the Stability of Fluorinated Calcium Aluminate and Borate Salts

Energy storage concepts based on multivalent ions, such as calcium, have great potential to become next-generation batteries due to their low cost and comparable cell voltage and energy density to Li-ion batteries. However, the development of Ca batteries is still hindered by the lack of suitable materials that grant a long cycle life. Specific to electrolyte materials, developing a calcium salt that is chemically stable under ambient conditions and enables reversible electrodeposition of Ca is critical. In this work, we use first-principles calculations to study the intrinsic and reductive stability of twelve Ca salts with fluorinated aluminate and borate anions and analyze the decomposition products formed on the metal anode surface that are critical to early-stage solid electrolyte interphase formation. Here we found anions with significant steric hindrance and a high degree of fluorination are intrinsically less stable and deemed unviable designs for Ca salt. Aluminate salts are generally less reactive with the Ca anode than their borate counterparts, and a high degree of fluorination leads to weaker reductive stability. Calcium fluoride is the most prominent decomposition product on the anode surface, and carbide-like motifs were also found from the decomposition of the designed salts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Acidity-Governed Rules in the Electrochemical Performance of Fluorinated Benzenes for High-Voltage Lithium Metal Batteries

Judicious selection of the optimal fluorobenzene (FB) as a nonsolvating cosolvent for lithium metal batteries (LMBs) is reported. For this work, we found the key correlation between FB structures and cycling stabilities of cells: increased fluorine substitution of FBs results in higher anodic stability but at the expense of reduced reductive stability, and FBs containing three or more fluorine atoms exhibit insufficient anodic stability in the electrolyte system comprised of fluoroethylene carbonate (FEC) and ethyl methyl carbonate (EMC). More importantly, FBs with higher acidity (lower pK a ) due to protons located between two adjacent fluorine atoms tend to be more susceptible to side reactions during cycling. Our results indicate that difluorobenzenes with no “acidic” proton (DFB2 and DFB4) have emerged as the optimal choice with the desired redox stability in high-voltage LMBs. Nuclear magnetic resonance and X-ray photoelectron spectroscopy confirmed these findings, providing guidance for selecting the most suitable FB variants as nonsolvating cosolvents for high-voltage LMBs.

25 ENERGY STORAGE↗
DOE OSTI2015

Role of precursor chemistry in the direct fluorination to form titanium based conversion anodes for lithium ion batteries

In this study, a new synthetic route for the formation of titanium oxydifluoride (TiOF 2 ) through the process of direct fluorination via a fluidized bed reactor system and the associated electrochemical properties of the powders formed from this approach are reported. The flexibility of this synthetic route was demonstrated using precursor powders of titanium dioxide (TiO 2 ) nanoparticles, as well as a reduced TiO x N y . An advantage of this synthetic method is the ability to directly control the extent of fluorination as a function of reaction temperature and time. The reversible capacity of TiOF 2 anodes was found to depend greatly upon the precursor employed. The TiOF 2 synthesized from TiO 2 and TiO x N y showed reversible capacities of 300 mAh g -1 and 440 mAh g -1 , respectively, over 100 cycles. The higher reversible capacity of the TiOF 2 powders derived from TiO x N y likely relate to the partial reduction of the Ti in the fluorinated electrode material, highlighting a route to optimize the properties of conversion electrode materials.

25 ENERGY STORAGE↗
DOE OSTI2020

Molecular insights into photostability of fluorinated organic photovoltaic blends: role of fullerene electron affinity and donor–acceptor miscibility

In this report, the photostability of certain organic photovoltaic (OPV) active layers was demonstrated to improve by as much as a factor of five under white light illumination in air with the use of 1,7-bis-trifluoromethylfullerene (C 60 (CF 3 ) 2 ) as the acceptor in place of PC 60 BM. However, the results were highly dependent on the structure and functionality within the donor material. Twelve combinations of active layer blends were studied, comprised of six different high-performance donor polymers (two fluorinated and four non-fluorinated donors) and two fullerene acceptors (PC 60 BM and C 60 (CF 3 ) 2 ). The relative rates of irreversible photobleaching of the active layer blends were found to correlate well with the electron affinity of the fullerene when the polymer and fullerene were well blended, but a full rationalization of the photobleaching data requires consideration of both the electron affinity of the fullerene as well as the relative miscibility of the polymer–fullerene components in the blend. Miscibility of those components was probed using a combination of time-resolved photoluminescence (TRPL) measurements and scanning tunneling microscopy (STM) imaging. The presence of fluorinated aromatic units in the donor materials tend to promote more intimate mixing with C 60 (CF 3 ) 2 as compared to PC 60 BM. The full results of these photobleaching studies and measurements of donor–acceptor miscibility, considered alongside additional photoconductance measurements and preliminary device work, provide new molecular optimization insights for improving the long-term stability of OPV active layers.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Physicochemical characterization of point defects in fluorine doped tin oxide films

The physical and chemical properties of spray deposited FTO films are studied using FESEM, x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), electrical and optical measurements. The results of XRD measurements showed that the films are polycrystalline (grain size 20-50 nm) with Rutile structure and mixed preferred orientation along the (200) and (110) planes. An angular shift of the XRD peaks after F-doping is observed and interpreted as being due to the formation of substitutional fluorine defects (F{sub O}) in presence of high concentration of oxygen vacancies (V{sub O}) that are electrically neutral. The electrical neutrality of oxygen vacancies is supported by the observation that the electron concentration n is two orders of magnitude lower than the V{sub O} concentration calculated from chemical analyses using XPS measurements. It is shown that an agreement between XPS, XRD, and Hall effect results is possible provided that the degree of deviation from stoichiometry is calculated with the assumption that the major part of the bulk carbon content is involved in O-C bonds. High temperature thermal annealing is found to cause an increase in the F{sub O} concentration and a decrease in both n and V{sub O} concentrations with the increase of the annealing temperature. These results could be interpreted in terms of a high temperature chemical exchange reaction between the SnO{sub 2} matrix and a precipitated fluoride phase. In this reaction, fluorine is released to the matrix and Sn is trapped by the fluoride phase, thus creating substitutional fluorine F{sub O} and tin vacancy V{sub Sn} defects. The enthalpy of this reaction is determined to be approximately 2.4 eV while the energy of formation of a V{sub Sn} through the migration of Sn{sub Sn} host atom to the fluoride phase is approximately 0.45 eV.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Influence of fluorine on the fiber resistance studied through the nonbridging oxygen hole center related luminescence

The distribution of Non-Bridging Oxygen Hole Centers (NBOHCs) in fluorine doped optical fibers was investigated by confocal microluminescence spectroscopy, monitoring their characteristic 1.9 eV luminescence band. The results show that these defects are generated by the fiber drawing and their concentration further increases after {gamma} irradiation. The NBOHC concentration profile along the fiber provides evidence for an exponential decay with the fluorine content. This finding agrees with the role of fluorine in the fiber resistance and is discussed, from the microscopic point of view, by looking at the conversion mechanisms from strained bonds acting as precursors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Fracture toughness of the sidewall fluorinated carbon nanotube-epoxy interface

The effects of carbon nanotube (CNT) sidewall fluorination on the interface toughness of the CNT epoxy interface have been comprehensively investigated. Nanoscale quantitative single-CNT pull-out experiments have been conducted on individual fluorinated CNTs embedded in an epoxy matrix, in situ, within a scanning electron microscope (SEM) using an InSEM{sup ®} nanoindenter assisted micro-device. Equations that were derived using a continuum fracture mechanics model have been applied to compute the interfacial fracture energy values for the system. The interfacial fracture energy values have also been independently computed by modeling the fluorinated graphene-epoxy interface using molecular dynamics simulations and adhesion mechanisms have been proposed.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Fluorinated graphene oxide for enhanced S and X-band microwave absorption

Here we report the microwave absorbing properties of three graphene derivatives, namely, graphene oxide (GO), fluorinated GO (FGO, containing 5.6 at. % Fluorine (F)), and highly FGO (HFGO, containing 23 at. % F). FGO is known to be exhibiting improved electrochemical and electronic properties when compared to GO. Fluorination modifies the dielectric properties of GO and hence thought of as a good microwave absorber. The dielectric permittivities of GO, FGO, and HFGO were estimated in the S (2 GHz to 4 GHz) and X (8 GHz to 12 GHz) bands by employing cavity perturbation technique. For this, suspensions containing GO/FGO/HFGO were made in N-Methyl Pyrrolidone (NMP) and were subjected to cavity perturbation. The reflection loss was then estimated and it was found that −37 dB (at 3.2 GHz with 6.5 mm thickness) and −31 dB (at 2.8 GHz with 6 mm thickness) in the S band and a reflection loss of −18 dB (at 8.4 GHz with 2.5 mm thickness) and −10 dB (at 11 GHz with 2 mm thickness) in the X band were achieved for 0.01 wt. % of FGO and HFGO in NMP, respectively, suggesting that these materials can serve as efficient microwave absorbers even at low concentrations.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Fluorinated graphene films with graphene quantum dots for electronic applications

This work analyzes carrier transport, the relaxation of non-equilibrium charge, and the electronic structure of fluorinated graphene (FG) films with graphene quantum dots (GQDs). The FG films with GQDs were fabricated by means of chemical functionalization in an aqueous solution of hydrofluoric acid. High fluctuations of potential relief inside the FG barriers have been detected in the range of up to 200 mV. A phenomenological expression that describes the dependence of the time of non-equilibrium charge emission from GQDs on quantum confinement levels and film thickness (potential barrier parameters between GQDs) is suggested. An increase in the degree of functionalization leads to a decrease in GQD size, the removal of the GQD effect on carrier transport, and the relaxation of non-equilibrium charge. The study of the electronic properties of FG films with GQDs has revealed a unipolar resistive switching effect in the films with a relatively high degree of fluorination and a high current modulation (up to ON/OFF ∼ 10{sup 4}–10{sup 5}) in transistor-like structures with a lower degree of fluorination. 2D films with GQDs are believed to have considerable potential for various electronic applications (nonvolatile memory, 2D connections with optical control and logic elements).

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Prediction of chlorine and fluorine crystal structures at high pressure using symmetry driven structure search with geometric constraints

The high-pressure properties of fluorine and chlorine are not yet well understood because both are highly reactive and volatile elements, which have made conducting diamond anvil cell and x-ray diffraction experiments a challenge. Here, we use ab initio methods to search for stable crystal structures of both elements at megabar pressures. We demonstrate how symmetry and geometric constraints can be combined to efficiently generate crystal structures that are composed of diatomic molecules. Furthermore, our algorithm extends the symmetry driven structure search method by adding constraints for the bond length and the number of atoms in a molecule while still maintaining generality. As a method of validation, we have tested our approach for dense hydrogen and reproduced the known molecular structures of Cmca-12 and Cmca-4. We apply our algorithm to study chlorine and fluorine in the pressure range of 10 GPa–4000 GPa while considering crystal structures with up to 40 atoms per unit cell. We predict chlorine to follow the same series of phase transformations as elemental iodine from Cmca to Immm to Fm3¯m, but at substantially higher pressures. We predict fluorine to transition from a C2/c to Cmca structure at 70 GPa, to a novel orthorhombic and metallic structure with P42/mmc symmetry at 2500 GPa, and finally to its cubic analog form with Pm3¯n symmetry at 3000 GPa.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Tetrafluoroethylene as a fuel component for an atomic fluorine generator of a supersonic continuous-wave chemical HF laser

A cheap and widely accessible combination (one of non-saturated perfluorocarbons), i.e. C{sub 2}F{sub 4} tetrafluoroethylene, is proposed as an alternative fuel component for an atomic fluorine generator of a supersonic cw chemical HF laser of self-contained type. Combustion products of the hypergolic F{sub 2} – C{sub 2}F{sub 4} – He mixture do not contain active relaxants of vibrationally excited HF(v) molecules. According to estimates, the atomic fluorine yield under comparable conditions is about 70 % in relation to that of the atomic fluorine generator operating on the F{sub 2} – D{sub 2} – He mixture which is the ‘basic’ one for a HF laser. The specific power is reduced by 23 % with an improvement in a set of the fuel performance and a significant reduction in the cost of triggering the laser in the course of its bench tests. (paper)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Increase in the Fluorine-Ion Conductivity of Single Crystals of Tysonite-type CeF{sub 3} Superionic Conductor by Substituting Polarized Cd{sup 2+} Ions for Ce{sup 3+} Ions

The fluorine-ion conductivity of single crystals with a tysonite (LaF{sub 3}) structure with heterovalent isomorphic substitutions of highly polarizable Cd{sup 2+} cations with a 18-electron shell for rare earth ions Ce{sup 3+} have been studied for the first time. Ce{sub 0.995}Cd{sub 0.005}F{sub 2.995} single crystals have been grown from melt by the Bridgman technique in a fluorinating atmosphere. The fluorine-ion conductivity of single crystal is measured by impedance spectroscopy in the temperature range from 153 to 1073 K, where it increases by a factor of 10{sup 9}, approaching the value σ{sub dc} = 5 × 10{sup –2} S/cm at 1073 K. At T{sub 0} = 450 ± 20 K, the dependence σ{sub dc}(T) is split into two portions with the ion-transport activation enthalpy ΔH{sub σ} = 0.39 ± 0.01 eV (T < T{sub 0}) and ΔH{sub σ} = 0.23 ± 0.02 eV (T > T0). It is found that at T = 293 K the conductivity σ{sub dc} = 3 × 10{sup –5} S/cm of Ce{sub 0.995}Cd{sub 0.005}F{sub 2.995} crystal is higher by a factor of 10 than the conductivity of the tysonite matrix CeF{sub 3} and close to the σ{sub dc} value for Ce{sub 0.995}Sr{sub 0.005}F{sub 2.995} crystal. This finding indicates a significant effect of the substitutions of Cd{sup 2+} ions for Ce{sup 3+} on the σdc value and the advantage of Cd{sup 2+} ions over Ca{sup 2+} and Ba{sup 2+} from the viewpoint of increasing σ{sub dc}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Fluorinated Electrolytes for 5-V Li-Ion Chemistry: Probing Voltage Stability of Electrolytes with Electrochemical Floating Test

A series of electrolyte formulations containing fluorinated cyclic carbonates and fluorinated linear carbonates with LiPF6 has been evaluated as electrolyte solvents for high-voltage Li-ion batteries. The anodic stability of the new electrolytes on fully charged spinel LiNi0.5Mn1.5O4 (LNMO) cathode was examined by electrochemical floating tests. The effects of fluorine substitution on the cyclic and linear carbonate, ratio of cyclic vs. linear carbonate, and LiPF6 concentration on the electrolyte oxidation stability were investigated. Based on this study, the floating test proved to be an effective tool for identification of stable electrolyte materials.

5-V LiNi0.5Mn1.5O4 cathode↗
DOE OSTI2015

Expedited Synthesis of Fluorine-18 Labeled Phenols. A Missing Link in PET Radiochemistry

Fluorine-18 (F-18) is arguably the most valuable radionuclide for positron emission tomographic (PET) imaging. However, while there are many methods for labeling small molecules with F-18 at aliphatic positions and on electron-deficient aromatic rings, there are essentially no reliable and practical methods to label electron-rich aromatic rings such as phenols, with F-18 at high specific activity. This is disappointing because fluorine-labeled phenols are found in many drugs; there are also many interesting plant metabolites and hormones that contain either phenols or other electron-rich aromatic systems such as indoles whose metabolism, transport, and distribution would be interesting to study if they could readily be labeled with F-18. Most approaches to label phenols with F-18 involve the labeling of electron-poor precursor arenes by nucleophilic aromatic substitution, followed by subsequent conversion to phenols by oxidation or other multi-step sequences that are often inefficient and time consuming. Thus, the lack of good methods for labeling phenols and other electron-rich aromatics with F-18 at high specific activity represents a significant methodological gap in F-18 radiochemistry that can be considered a “Missing Link in PET Radiochemistry”. The objective of this research project was to develop and optimize a series of unusual synthetic transformations that will enable phenols (and other electron-rich aromatic systems) to be labeled with F-18 at high specific activity, rapidly, reliably, and conveniently, thereby bridging this gap. Through the studies conducted with support of this project, we have substantially advanced synthetic methodology for the preparation of fluorophenols. Our progress is presented in detail in the sections below, and much has been published or presented publication; other components are being prepared for publication. In essence, we have developed a completely new method to prepare o-fluorophenols from non-aromatic precursors (diazocyclohexenones) by a novel reaction sequence that uses fluoride ion as a precursor and various activating electrophiles, and we have improved methods for the preparation of heterodiaryl iodonium salts. Both methods have been used to prepare interesting potential radiotracers. Other advances have been made in labeling dendrimeric nanoparticle structures of increasing interest for multimodal imaging and in advancing labeling through fluorosilane bonds. Thus, the progress we have made substantially fills the significant gap in PET radiochemistry that we originally identified, and it provides for the field new methodology that can be applied to a number of current challenges, including the preparation of several molecules of interest as radiotracers, such as 2-[18F]Fluoroestradiol (2-FES) and m-fluorotyrosine, which we have illustrated. These methods can be used by any skilled radiochemist interesting in preparing these agents or similar fluorine-18 labeled electron-rich arene systems of interested for PET biological imaging in the most general sense.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
NASA NTRS2002

Improved performance and safety of lithium ion cells with the use of fluorinated carbonate-based electrolytes

There has been increasing interest in developing lithium-ion electrolytes that possess enhanced safety characteristics, while still able to provide the desired stability and performance. Toward this end, our efforts have been focused on the development of lithium-ion electrolytes which contain partially and fully fluorinated carbonate solvents. The advantage of using such solvents is that they possess the requisite stability demonstrated by the hydrocarbon-based carbonates, while also possessing more desirable physical properties imparted by the presence of the fluorine substituents, such as lower melting points, increased stability toward oxidation, and favorable SEI film forming Characteristics on carbon. Specifically, we have demonstrated the beneficial effect of electrolytes which contain the following fluorinated carbonate-based solvents: methyl 2,2,2-trifluoroethyl carbonate (MTFEC), ethyl-2,2,2 trifluoroethyl carbonate (ETFEC), propyl 2,2,2-trifluoroethyl carbonate (PTFEC), methyl-2,2,2,2',2',2' -hexafluoro-i-propyl carbonate (MHFPC), ethyl- 2,2,2,2',2',2' -hexafluoro-i-propyl carbonate (EHFPC), and di-2,2,2-trifluoroethyl carbonate (DTFEC). These solvents have been incorporated into multi-component ternary and quaternary carbonate-based electrolytes and evaluated in lithium-carbon and carbon-LiNio.8Coo.202 cells (equipped with lithium reference electrodes). In addition to determining the charge/discharge behavior of these cells, a number of electrochemical techniques were employed (i.e., Tafel polarization measurements, linear polarization measurements, and electrochemical impedance spectroscopy (EIS)) to further characterize the performance of these electrolytes, including the SEI formation characteristics and lithium intercalatiodde-intercalation kinetics. In addition to their evaluation in experimental cells, cyclic voltammetry (CV) and conductivity measurements were performed on select electrolyte formulations to further our understanding of the trends in stability and ionic mobility imparted by different alkyl substituents in linear carbonates.

li-ion batteries fluorinated carbonate electrolyte↗
DOE OSTI2011

THE FIRST FLUORINE ABUNDANCE DETERMINATIONS IN EXTRAGALACTIC ASYMPTOTIC GIANT BRANCH CARBON STARS

Fluorine ({sup 19}F) abundances (or upper limits) are derived in six extragalactic asymptotic giant branch (AGB) carbon stars from the HF(1-0) R9 line at 2.3358 {mu}m in high-resolution spectra. The stars belong to the Local Group galaxies, Large Magellanic Cloud, Small Magellanic Cloud, and Carina dwarf spheroidal, spanning more than a factor of 50 in metallicity. This is the first study to probe the behavior of F with metallicity in intrinsic extragalactic C-rich AGB stars. Fluorine could be measured only in four of the target stars, showing a wide range in F enhancements. Our F abundance measurements together with those recently derived in Galactic AGB carbon stars show a correlation with the observed carbon and s-element enhancements. The observed correlations, however, display a different dependence on the stellar metallicity with respect to theoretical predictions in low-mass, low-metallicity AGB models. We briefly discuss the possible reasons for this discrepancy. If our findings are confirmed in a larger number of metal-poor AGBs, the issue of F production in AGB stars will need to be revisited.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Structural and Chemical Evolution of Highly Fluorinated Li‐Rich Disordered Rocksalt Oxyfluorides as a Function of Temperature

Abstract Li‐rich disordered rocksalt (DRS) oxyfluorides have emerged as promising high‐energy cathode materials for lithium‐ion batteries. While a high level of fluorination in DRS materials offers performance advantages, it can only be achieved via mechanochemical synthesis, which poses challenges of reproducibility and scalability. The definition of relationships between fluorination and structural stability is required to devise alternative methods that overcome these challenges. In this study, the thermal evolution of three highly fluorinated phases, Li 2 TMO 2 F (TM = Mn, Co, and Ni), is investigated in an inert atmosphere. Diffraction and spectroscopic techniques are utilized to examine their electronic and chemical states up until conditions of decomposition. The analysis reveals that the materials phase‐separate above 400 °C, at most. It is also observed that heat‐treated DRS materials exhibit intricate changes in the local coordination of the metals, including their spin, and ordering compared to the pristine states. The changes upon annealing are accompanied by a modulation of the voltage profile, including reduced hysteresis, when used as electrodes. These results provide an in‐depth understanding of the fundamental crystal chemistry of DRS oxyfluorides in view of their promising role as the next generation of Li‐ion cathodes.

25 ENERGY STORAGE↗
DOE OSTI2022

Binary Blend All‐Polymer Solar Cells with a Record Efficiency of 17.41% Enabled by Programmed Fluorination Both on Donor and Acceptor Blocks

Abstract Despite remarkable breakthrough made by virtue of “polymerized small‐molecule acceptor (PSMA)” strategy recently, the limited selection pool of high‐performance polymer acceptors and long‐standing challenge in morphology control impede their further developments. Herein, three PSMAs of PYDT‐2F, PYDT‐3F, and PYDT‐4F are developed by introducing different fluorine atoms on the end groups and/or bithiophene spacers to fine‐tune their optoelectronic properties for high‐performance PSMAs. The PSMAs exhibit narrow bandgap and energy levels that match well with PM6 donor. The fluorination promotes the crystallization of the polymer chain for enhanced electron mobility, which is further improved by following n ‐doping with benzyl viologen additive. Moreover, the miscibility is also improved by introducing more fluorine atoms, which promotes the intermixing with PM6 donor. Among them, PYDT‐3F exhibits well‐balanced high crystallinity and miscibility with PM6 donor; thus, the layer‐by‐layer processed PM6/PYDT‐3F film obtains an optimal nanofibril morphology with submicron length and ≈23 nm width of fibrils, facilitating the charge separation and transport. The resulting PM6/PYDT‐3F devices realizes a record high power conversion efficiency (PCE) of 17.41% and fill factor of 77.01%, higher than the PM6/PYDT‐2F (PCE = 16.25%) and PM6/PYDT‐4F (PCE = 16.77%) devices.

Zhou, Dehong↗