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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Conformal LiF Stabilized Interfaces via Electrochemical Fluorination on High Voltage Spinel Cathodes (≈4.9 V) for Lithium-Ion Batteries

The high voltage LiNi 0.5 Mn 1.5 O 4 (LNMO) spinel is one of the promising cathodes for the lithium-ion batteries due to its high energy densities, good rate performance. However, its high operating potential (≈4.75 V) causes extensive oxidation of conventional carbonate electrolytes, resulting an unstable and thick cathode electrolyte interphase (CEI) layer with a large irreversible capacity and low coulombic efficiency. In this work, we report the formation of thin LiF stabilized interfaces on LNMO via electrochemical fluorination that significantly improves the cycling stability and enhanced the capacity. An electrochemically induced conformal LiF layer acts as a part of a robust CEI by reducing the leakage of electrons and allowing the conduction of Li ions through it. Because of the robust LiF stabilized CEI, LNMO delivers a discharge capacity of ≈148.5 and ≈117.1 mAh g -1 at 0.1 and 1 C rate, respectively. It exhibits excellent cyclability with 80% capacity retention (CR) after 600 cycles in lithium-half cell and ≈90% CR after 200 cycles in full cell with only 0.03% and 0.05% capacity decay per cycle in conventional carbonate electrolytes without additives. Such an excellent electrochemical performance could lead to the potential development of high energy density batteries with high voltage cathodes for grid-based applications.

25 ENERGY STORAGE↗
DOE OSTI2026

Thermodynamic evaluation and modeling of the CeF 3 -LaF 3 -LiF-NaF system

The thermodynamic properties of the LiF-NaF-CeF 3 -LaF 3 pseudo-quaternary system have been evaluated, and models for the relevant phases have been revised or newly developed. The solid solubility of NaF in LaF 3 and CeF 3 was described in the model based on reported phase-equilibria observations and results from density functional theory calculations. The Gibbs energy functions for the NaCeF 4 and NaLaF 4 phases have been updated with recently reported thermochemical measurements. The Gibbs energy functions and model relations for the LiF-NaF-LaF 3 and LiF-NaF-CeF 3 pseudo-ternary systems were successfully optimized based on thermochemical properties and phase equilibria observations.

CALPHAD↗
DOE OSTI2023

An inorganic-rich but LiF-free interphase for fast charging and long cycle life lithium metal batteries

Abstract Li metal batteries using Li metal as negative electrode and LiNi 1-x-y Mn x Co y O 2 as positive electrode represent the next generation high-energy batteries. A major challenge facing these batteries is finding electrolytes capable of forming good interphases. Conventionally, electrolyte is fluorinated to generate anion-derived LiF-rich interphases. However, their low ionic conductivities forbid fast-charging. Here, we use CsNO 3 as a dual-functional additive to form stable interphases on both electrodes. Such strategy allows the use of 1,2-dimethoxyethane as the single solvent, promising superior ion transport and fast charging. LiNi 1-x-y Mn x Co y O 2 is protected by the nitrate-derived species. On the Li metal side, large Cs + has weak interactions with the solvent, leading to presence of anions in the solvation sheath and an anion-derived interphase. The interphase is surprisingly dominated by cesium bis(fluorosulfonyl)imide, a component not reported before. Its presence suggests that Cs + is doing more than just electrostatic shielding as commonly believed. The interphase is free of LiF but still promises high performance as cells with high LiNi 0.8 Mn 0.1 Co 0.1 O 2 loading (21 mg/cm 2 ) and low N/P ratio (~2) can be cycled at 2C (~8 mA/cm 2 ) with above 80% capacity retention after 200 cycles. These results suggest the role of LiF and Cs-containing additives need to be revisited.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Applications of LIF to Document Natural Variability of Chlorophyll Content and Cu Uptake in Moss

Chlorophyll has long been used as a natural indicator of plant health and photosynthetic efficiency. Laser-induced fluorescence (LIF) is an emerging technique for understanding broad spectrum organic processes and has more recently been used to monitor chlorophyll response in plants. Previous work has focused on developing a LIF technique for imaging moss mats to identify metal contamination with the current focus shifting toward application to moss fronds and aiding sample collection for chemical analysis. Two laser systems (CoCoBi a Nd:YGa pulsed laser system and Chl-SL with two blue continuous semiconductor diodes) were used to collect images of moss fronds exposed to increasing levels of Cu (1, 10, and 100 nmol/cm 2 ) using a CMOS camera. The best methods for the preprocessing of images were conducted before the analysis of fluorescence signatures were compared to a control. The Chl-SL system performed better than the CoCoBi, with dynamic time warping (DTW) proving the most effective for image analysis. Manual thresholding to remove lower decimal code values improved the data distributions and proved whether using one or two fronds in an image was more advantageous. A higher DTW difference from the control correlated to lower chlorophyll a/b ratios and a higher metal content, indicating that LIF, with the aid of image processing, can be an effective technique for identifying Cu contamination shortly after an event.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1980

Proton-induced degradation of VUV transmission of LiF and MgF2

Proton-induced degradation of vacuum ultraviolet (VUV) transmittance of LiF and MgF2 was measured for 85- and 600-MeV protons for a fluence up to 2.8 x 10 to the 13th p/sq cm. Transmittances were measured from 105 to 210 nm. When the irradiation level for a given material is expressed in terms of absorbed energy per unit of volume of crystal, 85- and 600-MeV protons produce the same degradation. MgF2 is substantially more radiation resistant than LiF in the VUV. Irradiation of LiF with 1.8 x 10 to the 13th p/sq cm at 85 MeV changed the transmittance of the hydrogen Ly-alpha line at 121.6 nm from 55 to 23%. The corresponding change for MgF2 was from 52 to 42% for 2.8 x 10 to the 13th p/sq cm.

Reft, C. S.↗
NASA NTRS1984

Fundamental Equations of the LIF Hydroxyl Measurements, Appendix a

The equation relating OH concentration to the observed detector count rate for a given laser flux is defined. That equation, which will be referred to henceforth as the central equation for absolute sensitivity, will be cast in terms of standard spectroscopic quantities such as oscillator strengths, Hoenl-London factors, rotational and vibrational quantum numbers, etc., such that it may be tested directly under laboratory conditions. The working expressions used by each of the OH laser induced fluorescence (LIF) groups will be related to this central equation, thereby establishing a common language for the comparison of experimental results and the definition of LIF system performance. The relevant structural details of the OH radical via a spectroscopic description of the energy levels and transitions employed in the LIF method are detailed. The central equation relating observed count rate to absolute concentration will be derived, and that equation will be related to the observed quantities cited by each of the experimental groups engaged in the measurement of OH in the Earth's atmosphere.

Source record↗
NASA NTRS1985

Laser-induced fluorescence of green plants. III - LIF spectral signatures of five major plant types

A technique amenable to remote sensing use which utilizes laser-induced fluorescence (LIF) properties of plants has been successfully used in the laboratory to identify five major plant types. These included herbaceous dicots, herbaceous monocots, conifers, hardwoods, and algae. Each of these plant types exhibited a characteristic LIF spectra when excited by a pulsed N2 laser emitting at 337 nm. Although monocots and dicots possess common fluorescence maxima at 440, 685, and 740 nm, they could be differentiated from one another by using the ratio of the square of the fluorescence intensity at 440 nm to the nonsquared intensity at 685 nm, i.e., (440)-squared/685. In all cases, monocots yielded a significantly higher ratio. Conifers have fluorescence maxima at 440, 525, and 740 nm but none at 685 nm. Hardwoods exhibited fluorescence at 440, 525, 685, and 740 nm. Algae had very low fluorescence at 440 nm, no fluorescence at 525 nm, and fluorescence maxima at 685 and 740 nm. For algae, the ratio of the fluorescence intensity at 685 nm to that at 740 nm was much greater than that for monocots, dicots, and hardwoods. The potential use of the LIF technique for individual species identification is suggested.

Chappelle, E. W.↗
NASA NTRS1990

Tensile properties of HA 230 and HA 188 after 400 and 2500 hour exposures to LiF-22CaF2 and vacuum at 1093 K

The solid-to-liquid phase transformation of the nominal LiF-20CaF2 eutectic at 1043 K is considered to be an ideal candidate thermal energy storage mechanism for a space based low temperature Brayton cycle solar dynamic system. Although Co, Fe, and Ni superalloys are thought to be suitable containment materials for LiF based salts, long term containment is of concern because molten fluorides are usually corrosive and Cr can be lost into space through evaporation. Two examples of commercially available superalloys in sheet form, the Ni-base material HA 230 and the Co-base material Ha 88, have been exposed to molten LiF-22CaF2, its vapor, and vacuum, at 1093 K, for 400 and 2500 hr. Triplicate tensile testing of specimens subjected to all three environments have been undertaken between 77 to 1200 K. Comparison of the weight gain data, microstructure, and tensile properties indicate that little, if any, difference in behavior can be ascribed to the exposure environment.

Whittenberger, J. Daniel↗
NASA NTRS1992

Mechanical properties of Haynes Alloy 188 after exposure to LiF-22CaF2, air, and vacuum at 1093 K for periods up to 10,000 hours

As part of a program to provide reassurance that the cobalt-base superalloy Haynes Alloy 188 can adequately contain a LiF-CaF2 eutectic thermal energy storage salt, 4900- and 10,000-hr exposures of Haynes Alloy 188 to LiF-22CaF2, its vapor, vacuum, and air at 1093 K have been undertaken. Following such exposures, the microstructure has been characterized and the 77 to 1200 K tensile properties measured. In addition, 1050 K vacuum creep-rupture testing of as-received and molten salt- and vacuum-exposed samples has been undertaken. Although slight degradation of the mechanical properties of Haynes Alloy 188 due to prior exposure was observed, basically none of the losses could be ascribed to a particular environment. Hence, observed decreases in properties are due to thermal aging effects, not corrosive attack. In view of these findings, Haynes Alloy 188 is still deemed to be suitable for containment of the eutectic LiF-CaF2 thermal energy storage media.

Whittenberger, J. D.↗
NASA NTRS1996

Soot Precursor Material: Spatial Location via Simultaneous LIF-LII Imaging and Characterization via TEM

The chemical and physical transformation between gaseous fuel pyrolysis products and solid carbonaceous soot represents a critical step in soot formation. In this paper, simultaneous two-dimensional LIF-LII (laser-induced fluorescence - laser-induced incandescence) images identify the spatial location where the earliest identifiable chemical and physical transformation of material towards solid carbonaceous soot occurs along the axial streamline in a normal diffusion flame. The identification of the individual LIF and LII signals is achieved by examining both the excitation wavelength dependence and characteristic temporal decay of each signal. Spatially precise thermophoretic sampling measurements are guided by the LIF-LII images with characterization of the sampled material accomplished via both bright and dark field TEM. Both bright and dark field TEM measurements support the observed changes in photophysical properties which account for conversion of fluorescence to incandescence as fuel pyrolysis products evolve towards solid carbonaceous soot.

VanderWal, Randall L.↗
DOE OSTI2026

Fading study of Harshaw LiF:Mg,Ti thermoluminescence dosimeters exposed to neutron doses

Sensitivity and signal fading were tested in Harshaw LiF:Mg,Ti thermoluminescence dosimeters (TLDs) exposed to neutron and beta/photons doses. A significant difference in the signal fading rate was observed for TLDs exposed to neutrons compared with TLDs exposed to betas. This difference may have been related to differences in glow curves for dosimeters exposed to different beams and to differences in glow curve evolution after exposure. A fading-correction algorithm was developed to correct the cumulative sensitivity + signal fading of TL doses for the fading time t using the formulae: y = 0.147∗exp(-t/4.36) + 0.308∗exp(-t/34.1) + 0.73 for neutrons, and: y = 0.132∗exp(-t/10.72) + 0.174∗exp(-t/31.5) + 0.8 for betas/photons. The formula was validated using the dose recovery test, where the average deviation of fading-corrected doses from delivery doses was within 1%. In conclusion, the proposed fading-correction approaches may significantly improve the accuracy of Harshaw TL dosimetry with LiF:Mg,Ti cards for both neutron and beta/gamma irradiation.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2025

2D photofragmentation LIF imaging of H 2 O 2 and HO 2 in the effluent of an atmospheric-pressure plasma jet: effects of solid and liquid interfaces

Two-dimensional (2D) absolute measurements of hydrogen peroxide (H 2 O 2 ) and approximations of the hydroperoxyl radical (HO 2 ) in the effluent of a COST Reference Microplasma Jet operated with a He/H 2 O feed gas are presented. Gas-phase densities are mapped using photofragmentation laser-induced fluorescence (PF-LIF) under three boundary conditions: open effluent, a solid target, and a liquid target. A novel method is presented for separating PF-LIF signals from H 2 O 2 and HO 2 using comparative measurements in oxygen-rich and oxygen-free environments to exploit the preferential formation of HO 2 in the presence of molecular oxygen. This separation strategy is supported by results from a plug-flow plasma chemistry model. Measured densities agree closely with model predictions in both magnitude and trend, while the 2D experimental distributions provide additional insight into the spatial dependencies of these species. In particular, the results show distinct differences in species transport depending on the target type: solid surfaces induce lateral deflection and reduced centerline densities, whereas liquid interfaces promote axial accumulation and higher near-axis concentrations.

atmospheric-pressure plasma jet (APPJ)↗
DOE OSTI2022

Dislocation-Limited Thermal Conductivity in LiF: Revisiting Perturbative Models

We revisit models to describe phonon-dislocation interactions and resulting dislocation-limited thermal conductivity (k), particularly as applied to describe the temperature-dependent k behavior of LiF with significant dislocation densities. Coupling semiempirical models of phonon scattering from dislocation strain fields provided by Klemens and Carruthers with density functional theory description of the phonons and input parameters, we find that both models significantly overpredict the measured k of LiF, as found previously. However, more direct application of the quantum perturbation theory description, from which the models were derived, gives significantly stronger phonon-dislocation scattering and strongly underpredicts the measured k data. We revisit the derivation of phonon-dislocation-strain field scattering and provide numerical details regarding its implementation. This work demonstrates that quantum perturbative calculations, now accessible to modern computational architectures, may provide a reasonable description of dislocation-limited k in materials as governed by phonon-strain field interactions provided that questions regarding the relevant strain field range can be resolved.

36 MATERIALS SCIENCE↗
DOE OSTI2023

An ab initio molecular dynamics study of varied compositions of the $\text{LiF-NaF-KF}$ molten salt

With increasing interest in molten salt reactors, there becomes a demand for investigations into thermophysical properties of salt systems. The LiF-NaF-KF (FLiNaK) salt system is a primary candidate for use in these reactors. However, the thermophysical properties of compositions outside the eutectic composition are still largely unknown. In this article, properties of ten unique compositions, including four ternary compositions, are investigated using ab initio molecular dynamics simulations across five temperatures between 900 K and 1300 K. The properties of interest are the density, thermal expansion, bulk modulus, compressibility, heat capacity, and enthalpy of mixing. In general, the results were found to be in good agreement with other literature and experimental results. The density and heat capacity had a tendency to be slightly underpredicted. No conclusions could be drawn about the bulk modulus and compressibility in terms of compositional dependence. The thermal expansion had a negative trend with respect to the LiF concentration and no trends were observed for the NaF or KF concentration. The enthalpy of mixing shows minima for the ternary compositions, with the near-equiatomic composition exhibiting the lowest values. Here this work shows the potential for compositional tailoring in the FLiNaK system to optimize thermophysical properties.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Electrolyte design for LiF-rich solid–electrolyte interfaces to enable high-performance microsized alloy anodes for batteries

Lithium batteries with Si, Al or Bi microsized (>10 µm) particle anodes promise a high capacity, ease of production, low cost and low environmental impact, yet they suffer from fast degradation and a low Coulombic efficiency. In this paper, we demonstrate that a rationally designed electrolyte (2.0 M LiPF 6 in 1:1 v/v mixture of tetrahydrofuran and 2-methyltetrahydrofuran) enables 100 cycles of full cells that contain microsized Si, Al and Bi anodes with commercial LiFePO 4 and LiNi 0.8 Co 0.15 Al 0.05 O 2 cathodes. Alloy anodes with areal capacities of more than 2.5 mAh cm -2 achieved >300 cycles with a high initial Coulombic efficiency of >90% and average Coulombic efficiency of >99.9%. These improvements are facilitated by the formation of a high-modulus LiF–organic bilayer interphase, in which LiF possesses a high interfacial energy with the alloy anode to accommodate plastic deformation of the lithiated alloy during cycling. Lastly, this work provides a simple yet practical solution to current battery technology without any binder modification or special fabrication methods.

25 ENERGY STORAGE↗
DOE OSTI2021

Electron leakage through heterogeneous LiF on lithium–metal battery anodes

The solid–electrolyte interphase (SEI) that forms on lithium ion battery (LIB) anodes prevents degradation-causing transfer of electrons to the electrolyte. Grain boundaries (GBs) between different SEI components, like LiF, have been suggested to accelerate Li+ transport. However, using the non-equilibrium Green's function technique with density functional theory (NEGF-DFT), we find that GBs enhance electron tunneling in thin LiF films by 1–2 orders of magnitude, depending on the bias. Extrapolating to thicker films using the Wentzel–Kramers–Brillouin (WKB) method emphasizes that safer batteries require passivation of GBs in the SEI.

25 ENERGY STORAGE↗
DOE OSTI2023

The Li + CaF → Ca + LiF chemical reaction under cold conditions

The calcium monofluoride (CaF) molecule has emerged as a promising candidate for precision measurements, quantum simulation, and ultracold chemistry experiments. Inelastic and reactive collisions of laser cooled CaF molecules in optical tweezers have recently been reported and collisions of cold Li atoms with CaF are of current experimental interest. In this paper, we report ab initio electronic structure and full-dimensional quantum dynamical calculations of the Li + CaF → LiF + Ca chemical reaction. The electronic structure calculations are performed using the internally contracted multi-reference configuration-interaction method with Davidson correction (MRCI + Q). An analytic fit of the interaction energies is obtained using a many-body expansion method. Furthermore, a coupled-channel quantum reactive scattering approach implemented in hyperspherical coordinates is adopted for the scattering calculations under cold conditions. Results show that the Li + CaF reaction populates several low-lying vibrational levels and many rotational levels of the product LiF molecule and that the reaction is inefficient in the 1–100 mK regime allowing sympathetic cooling of CaF by collisions with cold Li atoms.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Multistage nucleation pathway in LiF molten salt mirrors the crystal–melt interface structure

Despite over a century of studies, fundamental questions remain about the processes governing crystal nucleation from melts or solutions. Research over the past three decades has presented mounting evidence for kinetic pathways of crystal nucleation that are more complex than envisioned by the simplest forms of classical theory. Such observations have been presented for colloidal and elemental systems with covalent and metallic bonding. Despite the technological and geochemical importance of molten salts, similar studies for these ionically bonded systems are currently lacking. Here we develop a machine learning interatomic potential for a model ionic system: LiF. The potential features quantum-level accuracy for both liquid and multiple solid polymorphs over wide temperature and pressure ranges and accurately reproduces experimentally measured properties. Thanks to the efficiency of the potential, which enables microsecond-scale molecular dynamics simulations, induction times for nucleation of LiF solids from their melts are computed over a range of undercoolings. With the aid of a set of robust local order parameters established here, the simulations reveal that homogeneous crystal nucleation in undercooled melts preferentially initiates from liquid regions showing slow dynamics and high bond orientational order simultaneously, and the second-shell order of both precritical nuclei and the surface of postcritical nuclei is dominated by hexagonal close packing and body-centered cubic local structure, even though the nucleus core is dominated by face-centered cubic structure corresponding to the stable rocksalt crystal structure. Finally, we establish a connection between the crystallization pathway and the equilibrium crystal-melt interface structure.

Applied Physical Sciences↗