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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Electrochemical fluorination of trichloroethylene and N, N-dimethyltrifluoroacetamide

The paper presents the results of experiments concerning the fluorination of trichloroethylene and N, N-dimethyltrifluoroacetamide carried out on a laboratory scale in an advanced 'Simons' type electrochemical apparatus which could be operated automatically from ambient to 50 psi pressure. It is shown that a variety of fluorine-substituted products are formed, depending upon electrolysis conditions and concentrations of reactant relative to the NaF, KF, HF electrolyte. A new reaction mechanism of electrochemical fluorination of trichloroethylene is proposed. Finally, the solvency-to-fluorine content relationship of fluorinated N, N-dimethyltrifluoroacetamide is described.

Hsu, L.-C.↗
DOE OSTI2023

Direct Mapping of Fluorine in Cation Disordered Rocksalt Cathodes

Cation-disordered rocksalt (DRX) oxides are promising candidates as next-generation cathodes for lithium-ion batteries. Partial fluorination of the DRX oxides enhances their cyclability. However, the lattice position, concentration, and spatial distribution of fluorine within DRX lattices remain elusive. Here, in this work, we use atom location by channeling-enhanced microanalysis, energy-dispersive X-ray spectroscopy, electron energy loss spectroscopy, and integrated differential phase contrast imaging in a scanning transmission electron microscope to gain atomic-level insights into DRX with nominal composition of Li 1.2 Mn 0.7 Ti 0.1 O 1.7 F 0.3 and Li 1.15 Ni 0.45 Ti 0.3 Mo 0.1 O 1.85 F 0.15 . We reveal that fluorine substitutes oxygen in the DRX lattices. The O/F ratio in terms of O+F = 2 is in the range from 1.92:0.08 to 1.82:0.18. Spatially, fluorine is distributed in the proximity of the Li-rich regions but distinct from lithium fluoride. Additionally, we observe that incorporation of fluorine in the DRX lattice induces a larger variation in cation–anion separation. These observations provide insight into the guided design of oxyfluoride DRX cathodes for high-performance batteries.

(S)TEM↗
DOE OSTI2020

Effect of fluorination and Li-excess on the Li migration barrier in Mn-based cathode materials

Disordered rocksalt (DRX) Li-rich transition metal (TM) oxides, especially those based on Mn, are prospective high-energy-density cathode materials for the next generation of Li-ion batteries that use earth abundant metals. Fluorine substitution on the oxygen sublattice has been shown to reduce oxygen redox by lowering the average anion valence and increasing the amount of redox-active TM, and simultaneously improve energy density, average voltage and capacity retention. While these benefits of fluorination are well established, it is not well understood how F affects Li transport and therefore the rate performance of Mn-based DRX cathodes. Herein, we investigate the effects of both F substitution and the accompanying Li-excess on Li migration barriers using first-principles calculations. Finally, we demonstrate that F has a small negative effect on Li migration barriers while Li-excess decreases Li migration barriers. Because fluorination enables more Li-excess, these results do not predict any detrimental impact on Li transport.

25 ENERGY STORAGE↗
DOE OSTI2020

Effect of Fluorination on Lithium Transport and Short-Range Order in Disordered-Rocksalt-Type Lithium-Ion Battery Cathodes

Fluorine substitution is a critical enabler for improving the cycle life and energy density of disordered rocksalt (DRX) Li-ion battery cathode materials which offer prospects for high energy density cathodes, without the reliance on limited mineral resources. Due to the strong Li–F interaction, fluorine also is expected to modify the short-range cation order in these materials which is critical for Li-ion transport. In this work, density functional theory and Monte Carlo simulations are combined to investigate the impact of Li–F short-range ordering on the formation of Li percolation and diffusion in DRX materials. Additionally, the modeling reveals that F substitution is always beneficial at sufficiently high concentrations and can, surprisingly, even facilitate percolation in compounds without Li excess, giving them the ability to incorporate more transition metal redox capacity and thereby higher energy density. It is found that for F levels below 15%, its effect can be beneficial or disadvantageous depending on the intrinsic short-range order in the unfluorinated oxide, while for high fluorination levels the effects are always beneficial. Using extensive simulations, a map is also presented showing the trade-off between transition-metal capacity, Li-transport, and synthetic accessibility, and two of the more extreme predictions are experimentally confirmed.

25 ENERGY STORAGE↗
DOE OSTI2020

Ultrafast Exciton Transport with a Long Diffusion Length in Layered Perovskites with Organic Cation Functionalization

Abstract Layered perovskites have been employed for various optoelectronic devices including solar cells and light‐emitting diodes for improved stability, which need exciton transport along both the in‐plane and the out‐of‐plane directions. However, it is not clear yet what determines the exciton transport along the in‐plane direction, which is important to understand its impact toward electronic devices. Here, by employing both steady‐state and transient photoluminescence mapping, it is found that in‐plane exciton diffusivities in layered perovskites are sensitive to both the number of layers and organic cations. Apart from exciton–phonon coupling, the octahedral distortion is revealed to significantly affect the exciton diffusion process, determined by temperature‐dependent photoluminescence, light‐intensity‐dependent time‐resolved photoluminescence, and density function theory calculations. A simple fluorine substitution to phenethylammonium for the organic cations to tune the structural rigidity and octahedral distortion yields a record exciton diffusivity of 1.91 cm 2 s −1 and a diffusion length of 405 nm along the in‐plane direction. This study provides guidance to manipulate exciton diffusion by modifying organic cations in layered perovskites.

Xiao, Xun↗
DOE OSTI2022

Fluoro‐nitrogen Cations

Abstract The crystal structures of [NH 3 F] + [CF 3 SO 3 ] − , [NH 2 F 2 ] + [SbF 6 ] − , and [N 2 F 3 ] + [Sb 3 F 16 ] − have been determined, representing the first structural characterizations of these simple fluoro‐nitrogen cations. The influences of the hybridization of the central nitrogen atom and of the number of fluorine substituents on the N−F bond lengths are evaluated for the series N 2 F + , N 2 F 3 + , NF 2 O + , NH 3 F + , NH 2 F 2 + , and NF 4 + . It is shown that the N−F bond length decreases from 1.40 Å to 1.26 Å with increasing fluorine substitution and increasing s‐character of the nitrogen atom, and that unusual N−F bond lengths reported in the previous literature are caused by disorder problems

Vij, Ashwani↗
DOE OSTI2021

Fluoro–nitrogen Cations

The crystal structures of [NH 3 F] + [CF 3 SO 3 ] – , [NH 2 F 2 ] + [SbF 6 ] – , and [N 2 F 3 ] + [Sb 3 F 16 ] – have been determined, representing the first structural characterizations of these simple fluoro-nitrogen cations. The influences of the hybridization of the central nitrogen atom and of the number of fluorine substituents on the N–F bond lengths are evaluated for the series N 2 F + , N 2 F 3 + , NF 2 O + , NH 3 F + , NH 2 F 2 + , and NF 4 + . Here it is shown that the N–F bond length decreases from 1.40 Å to 1.26 Å with increasing fluorine substitution and increasing s-character of the nitrogen atom, and that unusual N–F bond lengths reported in the previous literature are caused by disorder problems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Decomposition of PVDF to delaminate cathode materials from end-of-life lithium-ion battery cathodes

The growing demand of electric vehicles and rapid consumption of rechargeable lithium-ion batteries (LIBs) require recycling of spent cathode active materials (CAMs) to reduce hazardous wastes and supply raw materials to LIB production. To separate CAMs from the cathode, direct calcination of polyvinylidene fluoride (PVDF) binder is widely applied, which leads to high energy consumption and release of toxic hydrogen fluoride. It is desirable to have an environmentally friendly and effective alternative to traditional direct calcination. In this study, five lithium salts, LiOAc (lithium acetate), LiNO 3 , LiCl, Li 2 CO 3 , and Li 2 SO 4 , were deployed and compared for their performance in recycling CAMs. A peel-off efficiency of up to 98.5% was achieved at a LiOAc to LiNO 3 molar ratio of 3:2, salt to cathode mass ratio of 10:1, and temperature of 300 °C at a holding time of 30 min. This system avoids corrosive chemicals and minimizes particle agglomeration of recycled products. Compared with sodium salt systems (NaOAc-NaNO 3 ) or direct calcination, the LiOAc-LiNO 3 system prevented high reaction temperature or further lithium loss and minimized crystal structure and morphological changes. In conclusion, a decomposition mechanism of PVDF through adsorption of HF and fluorine substitution was proposed.

25 ENERGY STORAGE↗
DOE OSTI2023

Deep and Shallow Gap States in Reduced and n-Type Doped m -ZrO 2

Monoclinic zirconium dioxide (m-ZrO 2 ) is a wide-band-gap functional oxide with many applications. Understanding the role of intrinsic defects and dopants is important for improving the properties of m-ZrO 2 relevant to its applications. In this work, we characterize the electronic states and energy levels of oxygen vacancies (VO’s) and n-type Nb, Ta, Rb, H, and F dopants in the bulk and at the majority (1̅11) surface of m-ZrO 2 , using accurate dielectric-dependent hybrid functional calculations. Our results show that VO’s generally behave as deep donors with the excess electrons localized at the vacant O sites in the form of F centers, in agreement with previous studies. In contrast, surface VO’s at two-fold coordinated oxygen sites show a rather shallow (1+/0) transition level. Shallow levels are also obtained for adsorbed hydrogen (H ads ) and fluorine substituting an oxygen atom (FO) either in the bulk or at the surface, whereas Nb and Ta form deep levels. Altogether, our results suggest that FO is the best candidate for realizing n-type conductivity in bulk m-ZrO 2 , while surface VO’s and Hads provide an efficient way to control the surface chemistry of m-ZrO 2 .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Ultrahigh power and energy density in partially ordered lithium-ion cathode materials

There is an intensive search for high-performance cathode materials for rechargeable batteries. In this work the authors report that oxyfluorides with partial spinel-like cation order, made from earth-abundant elements, display both exceptionally high energy and power. The rapid market growth of rechargeable batteries requires electrode materials that combine high power and energy and are made from earth-abundant elements. In this paper we show that combining a partial spinel-like cation order and substantial lithium excess enables both dense and fast energy storage. Cation overstoichiometry and the resulting partial order is used to eliminate the phase transitions typical of ordered spinels and enable a larger practical capacity, while lithium excess is synergistically used with fluorine substitution to create a high lithium mobility. With this strategy, we achieved specific energies greater than 1,100 Wh kg -1 and discharge rates up to 20 A g -1 . Remarkably, the cathode materials thus obtained from inexpensive manganese present a rare case wherein an excellent rate capability coexists with a reversible oxygen redox activity. Our work shows the potential for designing cathode materials in the vast space between fully ordered and disordered compounds.

25 ENERGY STORAGE↗
NASA NTRS1982

Heat-Exchange Fluids for Sulfuric Acid Vaporizers

Some fluorine-substituted organic materials meet criteria for heat-exchange fluids in contact with sulfuric acid. Most promising of these are perfluoropropylene oxide polymers with degree of polymerization (DP) between 10 and 50. It is desirable to have DP in high range because vapor pressure of material decreases as DP increases, and high-DP liquids have lower loss due to vaporization.

Lawson, D. D.↗
NASA NTRS1989

Improved high-temperature resistant matrix resins

A study was performed with the objective of developing matrix resins that exhibit improved thermo-oxidative stability over state-of-the-art high temperature resins for use at temperatures up to 644 K (700 F) and air pressures up to 0.7 MPa (100 psia). The work was based upon a TRW discovered family of polyimides currently licensed to and marketed by Ethyl Corporation as EYMYD(R) resins. The approach investigated to provide improved thermo-oxidative properties was to use halogenated derivatives of the diamine, 2, 2-bis (4-(4-aminophenoxy)phenyl) hexafluoropropane (4-BDAF). Polyimide neat resins and Celion(R) 12,000 composites prepared from fluorine substituted 4-BDAF demonstrated unexpectedly lower glass transition temperatures (Tg) and thermo-oxidative stabilities than the baseline 4-BDAF/PMDA polymer.

Green, H. E.↗
NASA NTRS1989

ESCA Study of Poly (Vinylidene Fluoride) Tetrafluoroethylene - Ethylene Copolymer and Polyethylene Exposed to Atomic Oxygen

The ESCA (electron spectroscopy for chemical analysis) spectra of films of poly(vinylidene fluoride) (PVDF), tetrafluoroethylene-ethylene copolymer (TFE/ET) and polyethylene (PE) exposed to atomic oxygen (O(P-3)), in or out of the glow of a radio-frequency O2 plasma, were compared. ESCA spectra of PE films exposed to (O(P-3)) in low Earth orbit (LEO) on the STS-8 Space Shuttle were also examined. Apart from O(P-3)-induced surface recession (etching), the various polymer films exhibited surface oxidation, which proceeded towards equilibrium saturation oxygen levels. The maximum surface oxygen uptakes for in-glow or out-of-glow exposures were in the order: PE greater than TFE/ET greater than PVDF; for PE itself, the oxygen uptakes were in the order: in glow greater than out of glow greater than LEO. Given prior ESCA data on poly(vinyl fluoride) and polytetrafluoroethylene films exposed to O(P-3), the extent of surface oxidation is seen to decrease regularly with increase in fluorine substitution in a family of ethylene-type polymers. (Keywords: ESCA; poly(vinylidene fluoride); tetrafluoroethylene ethylene copolymer; polyethylene; atomic oxygen; radio-frequency oxygen plasma; low Earth orbit)

Golub, Morton A.↗
DOE OSTI2025

Fluorinated polythiophenes with ester side chains for boosting the V OC and efficiency in non-fullerene polymer solar cells

As the power conversion efficiency (PCE) of organic photovoltaics (OPVs) approximates the 19 % threshold, wide bandgap (WBG) polythiophenes (PTs) have gained increasing attention due to their simple chemical structures and ease of synthesis, making them promising candidates for large-scale production. However, the benchmark polymer poly(3-hexylthiophene) (P3HT) is limited by its high-lying HOMO energy level, which restricts the open-circuit voltage (V OC ) in solar cells. Here, in this study, we introduce a novel series of PT derivatives (PDC8-T, PDC8-3T, PDC16-3T, and PDC16-3T-2F) featuring ester side chains designed to fine-tune electronic properties through a streamlined three-step synthesis. Additionally, we incorporated a π-spacer to reduce steric hindrance and elongated alkyl side chains to improve solubility and processability. Compared to P3HT, these PT derivatives demonstrate a significant reduction in HOMO energy levels, lowering by approximately 0.3–0.4 eV. Among them, PDC16-3T-2F—with fluorine atom substitution—achieves the lowest HOMO energy level, induces a coplanar molecular conformation, and enhances polymer aggregation behavior. We evaluated these PT derivatives in inverted non-fullerene bulk-heterojunction (NFA BHJ) OPVs. The PDC8-3T device showed a relatively low PCE of 0.69 %, with a V OC of 0.76 V, a short-circuit current density (J SC ) of 3.32 mA/cm 2 , and a fill factor (FF) of 27.3 %. In contrast, the PDC16-3T-2F device achieved an impressive PCE of 7.21 %, with a V OC of 0.85 V, a J SC of 14.60 mA/cm 2 , and an FF of 58.4 %. This remarkable improvement is attributed to the fluorine substitution, which not only enhances molecular orientation but also downshifts the HOMO energy level and further boosts the V OC . Hence, these molecular design strategies have led to a fibrillar bicontinuous interpenetrating network with optimal nanoscale phase separation within the active layer.

14 SOLAR ENERGY↗
NASA NTRS1998

Effect of halogenation on the nonlinear optical properties of porthyrin and substituted porphyrins

The effect that fluorine and chlorine substitution has on the nonlinear optical properties of porphyrin, tetramethylporphyrin and tetraphenylporphyrin has been theoretically studied. The calculations of nonlinear optical properties have been obtained by performing finite-field calculations on structures determined by semiempirical methods. In addition, tetra(p-chlorophenyl)porphyrin and tetra(p-bromophenyl)porphyrin were synthesized by the condensation of pyrrol and the appropriate aldehyde. Thin films of polymethylmethacrylate were obtained containing these materials, by spin coating onto glass substrates. The films were characterized by third-harmonic generation. It was determined that the experimental conditions enhance the third-order polarizability of the tetraphenylporphyrins by a factor of about 1.6.

Cardelino, Beatriz H.↗
DOE OSTI2026

Point defects and impurities in fluorite PuO 2

The native surface oxide of plutonium plays a critical role in ensuring the stability and safe storage of the underlying metal; consequently, understanding the role of defects and impurities in determining the properties of the oxide layer is critical. Here, in this study, we use hybrid density-functional theory calculations to evaluate the electronic structure and defect chemistry of PuO 2 , the most stable of the native oxide phases, including both native and extrinsic defects. We find that oxygen vacancies (𝑉 O ) form readily in PuO 2 , as do polarons. Electron polarons (𝜂 − ) are the lowest-energy acceptor species in PuO 2 , while the charge compensating donor species will shift from 𝑉 O under O-poor conditions to hole polarons (𝜂 + ) under O-rich conditions. Nitrogen and fluorine can substitute readily for oxygen atoms under O-poor conditions, while fluorine can also incorporate in an interstitial configuration (F$^−_i$) under more O-rich conditions. Carbon and chlorine incorporation in PuO 2 will be very limited. We also evaluate the kinetic barriers for oxygen-related defects, which we find to diffuse readily when present. Our results provide valuable insights into the critical role and variable chemistry of point defects and impurities in PuO 2 , which in turn have important implications for the safe storage of the underlying metal layer. In short, exposure of freshly prepared plutonium to reactive nitrogen- and fluorine-containing contaminants should be avoided, while carbon- or chlorine-containing contaminants are less likely to incorporate readily into the oxide.

Materials science↗
DOE OSTI2021

Understanding cation-disordered rocksalt oxyfluoride cathodes

Partial fluorine (F) substitution into the oxygen (O) sublattice has been shown to improve cycling stability of cation-disordered Li-excess rocksalt oxide (DRX) cathodes. Detailed understanding on failure mechanisms and key optimization knowledge of fluorinated-DRX (F-DRX), however, are lacking. In the present study, we incorporate different amounts of F into a baseline DRX system, Li 1.2 Ti 0.4 Mn 0.4 O 2 (LTMO3.0, 3.0 denotes nominal Li/Mn ratio), and synthesize two oxyfluoride compounds, Li-rich Li 1.3 Ti 0.3 Mn 0.4 O 1.7 F 0.3 (LTMOF3.25) and Mn-rich Li 1.2 Ti 0.2 Mn 0.6 O 1.8 F 0.2 (LTMOF2.0) with an increased and reduced Li/Mn ratio of 3.25 and 2.0, respectively. Through careful monitoring of chemical and structural evolution, we show that cycling-induced changes are manifested not only by Mn reduction and degradation of its local coordination environment, but also by F enrichment and formation of LiF-type of domains on the surface. A “concerted-densification” based failure mechanism, involving atomic-level changes in both transition-metal cationic sublattice and oxygen/fluorine anionic sublattice, is proposed for the degradation in F-DRX cathode materials. The study reveals that increasing F content accompanied by reduced Li/Mn ratio mitigates the degradation process, offering key design strategies in achieving balanced cathode capacity and stability.

25 ENERGY STORAGE↗