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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Thermoelasticity Model for Lithium Fluoride

Lithium fluoride (LiF) is a typical ionic solid, and at the same time a typical polymorphic (multi-phase) material. Its phase diagram contains two solid phases, B1 (rock salt) and B2 (CsCl), which are typical of ionic solids. The phase diagram of LiF was suggested by Smirnov. We have carried out extensive study of the properties of LiF using one of the most recent versions of VASP (Vienna Ab initio Simulation Package) which allows one to carry out calculations on ionic solids; more detail will be presented elsewhere.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Development of a lithium fluoride zinc sulfide based neutron multiplicity counter

Past 3He shortages led to investigations into replacement options for neutron detectors in systems that previously used 3He-based technologies. The goal of this research was to investigate the feasibility of a full-scale lithium fluoride with silver activated zinc sulfide (LiF/ZnS) based neutron multiplicity counter. The LiF/ZnS based neutron multiplicity counter (LiNMC) was developed based on an iterative process between modeling and experimental measurements. Each active region of the LiNMC contains five sheets of LiF/ZnS sandwiched between six sheets of wavelength shifting plastic to form neutron detection stacks. The wavelength shifted scintillation light was collected by photomultiplier tubes located on each end of the stacks. Twelve such detector stacks were placed around a sample chamber in a square arrangement with lithiated high density polyethylene blocks in the corners to reflect high energy neutrons and capture low energy neutrons. Preliminary calibration with a 252Cf neutron source showed that the LiNMC was able to achieve 36% neutron detection efficiency (ε) and an 11.7 μs neutron die-away time (τ) for a doubles Figure-of-merit (ε2/ τ) of 109. This is the highest doubles Figure-of-merit performance measured to-date for a 3He-free neutron multiplicity counter system. By the end of this project, the LiNMC’s basic components were integrated into a single laboratory scale system capable of proof-of-concept measurements.

3He-free↗
DOE OSTI2018

Novel ALD Chemistry Enabled Low-Temperature Synthesis of Lithium Fluoride Coatings for Durable Lithium Anodes

Lithium metal anodes can largely enhance the energy density of rechargeable batteries because of the high theoretical capacity and the high negative potential. However, the problem of lithium dendrite formation and low Coulombic efficiency (CE) during electrochemical cycling must be solved before lithium anodes can be widely deployed. Herein, a new atomic layer deposition (ALD) chemistry to realize the low-temperature synthesis of homogeneous and stoichiometric lithium fluoride (LiF) is reported, which then for the first time, as far as we know, is deposited directly onto lithium metal. The LiF preparation is performed at 150 °C yielding 0.8 Å/cycle. The LiF films are found to be crystalline, highly conformal, and stoichiometric with purity levels >99%. Nanoindentation measurements demonstrate the LiF achieving a shear modulus of 58 GPa, 7 times higher than the sufficient value to resist lithium dendrites. When used as the protective coating on lithium, it enables a stable Coulombic efficiency as high as 99.5% for over 170 cycles, about 4 times longer than that of bare lithium anodes. The remarkable battery performance is attributed to the nanosized LiF that serves two critical functions simultaneously: (1) the high dielectric value creates a uniform current distribution for excellent lithium stripping/plating and ultrahigh mechanical strength to suppress lithium dendrites; (2) the great stability and electrolyte isolation by the pure LiF on lithium prevents parasitic reactions for a much improved CE. Here, this new ALD chemistry for conformal LiF not only offers a promising avenue to implement lithium metal anodes for high-capacity batteries but also paves the way for future studies to investigate failure and evolution mechanisms of solid electrolyte interphase (SEI) using our LiF on anodes such as graphite, silicon, and lithium.

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

Two-phase equation of state for lithium fluoride

Here, we present an equation of state for the solid and liquid phases of lithium fluoride that covers a wide range of conditions from ambient pressure and temperature to the high pressures and temperatures exhibited in shock- and ramp-compression studies. The particular solid phase we have focused on in this work is the B1 phase. We have followed an approach where the pressure and heat-capacity functions of both phases are fit to experimental data and our own quantum molecular dynamics simulations and are then integrated in a thermodynamically consistent way to obtain the corresponding free-energy functions. This approach yields a two-phase equation of state that provides better overall agreement with experimental data than other equations of state for lithium fluoride, such as SESAME 7271v3, LEOS 2240, and the model presented by Smirnov. The last of these is a three-phase equation of state that predicts a B1–B2 transition along the shock Hugoniot at a pressure of about 140 GPa. This solid–solid transition has been a topic of speculation and debate in the literature for over 50 years, culminating in the work of Smirnov, who has developed the only potentially viable equation of state that allows for this transition. We explain why the proposed B1–B2 transition at 140 GPa is not consistent with recent velocimetry data.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Compression behavior of lithium fluoride up to 80 GPa and 2300 K

Here, the high-temperature compression behavior of lithium fluoride (LiF) has been determined to ∼80 GPa and 2300 K by means of high-resolution synchrotron-based x-ray diffraction in a laser-heated diamond-anvil cell. The room-temperature Vinet equation of state (EOS) for LiF yields an isothermal room-temperature, ambient-pressure lattice parameter a 0 = 4.028 (±0.003) Å, volume V 0 = 65.35 (±0.03) Å 3 , bulk modulus K 0 = 67.57 (±0.34) GPa, and its pressure derivative K 0 ’ = 4.64 (±0.03). This expanded experimental dataset is in good agreement with the LiF thermal equation of state by Myint et al. (2019) up to ∼2300 K and 25 GPa. At higher pressures and temperatures our data shows reduced thermal expansion compared to the prediction and may be particularly important for experiments at more extreme conditions.

High-pressure behavior↗
DOE OSTI2019

Refractive index of lithium fluoride to 900 gigapascal and implications for dynamic equation of state measurements

Lithium fluoride (LiF) is a unique crystal possessing the largest reported bandgap of any material and is predicted to remain transparent to visible light under stresses in excess of 1000 GPa. Dynamic compression experiments often utilize LiF as a window material to maintain stress on a sample while enabling direct measurements of interface velocity. However, typical velocimetry diagnostics measure changes in the optical path length; therefore, an accurate understanding of LiF’s equation of state and refractive index is needed. Here, we present a measurement of the LiF refractive index up to 900 GPa from a low-temperature ramp-compression experiment at the National Ignition Facility. To demonstrate propagation of optical uncertainty from this work to equation of state measurements, simulations in which a tin–LiF interface reaches a peak stress of 825 GPa show that the principal isentrope of tin can be determined up to 1450 GPa with a 1.2% uncertainty in density while considering uncertainties in the optical response of LiF.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Nuclear recoil detection with color centers in bulk lithium fluoride

We present initial results on the detection of nuclear recoils in lithium fluoride (LiF) through the fluorescence of color centers created by particle interactions in the crystal lattice. Using light-sheet fluorescence microscopy, we image nuclear recoil tracks from both fast and thermal neutron interactions deep within a cubic-centimeter-scale sample. Automated three-dimensional feature extraction based on machine-learning tools enables the identification and classification of individual events. We observe that the fluorescence response of LiF to gamma irradiation is strongly suppressed, by a factor of 30–50 compared to neutron exposure, demonstrating intrinsic insensitivity to electromagnetic backgrounds. The observed and simulated event characteristics are consistent, including their number, size, and topology. These results establish the feasibility of LiF as a scalable detection medium for rare nuclear-recoil events and constitute a first step toward 10–1000 g scale detectors with single-event sensitivity for applications in reactor-neutrino detection, neutron spectroscopy, and dark matter searches.

Aroujo, G R [University of Zurich]↗
DOE OSTI2017

Conformal Lithium Fluoride Protection Layer on Three-Dimensional Lithium by Nonhazardous Gaseous Reagent Freon

Research on lithium (Li) metal chemistry has been rapidly gaining momentum nowadays not only because of the appealing high theoretical capacity, but also its indispensable role in the next-generation Li–S and Li–air batteries. However, two root problems of Li metal, namely high reactivity and infinite relative volume change during cycling, bring about numerous other challenges that impede its practical applications. In the past, extensive studies have targeted these two root causes by either improving interfacial stability or constructing a stable host. However, efficient surface passivation on three-dimensional (3D) Li is still absent. Here in this paper, we develop a conformal LiF coating technique on Li surface with commercial Freon R134a as the reagent. In contrast to solid/liquid reagents, gaseous Freon exhibits not only nontoxicity and well-controlled reactivity, but also much better permeability that enables a uniform LiF coating even on 3D Li. By applying a LiF coating onto 3D layered Li-reduced graphene oxide (Li-rGO) electrodes, highly reduced side reactions and enhanced cycling stability without overpotential augment for over 200 cycles were proven in symmetric cells. Furthermore, Li–S cells with LiF protected Li-rGO exhibit significantly improved cyclability and Coulombic efficiency, while excellent rate capability (~800 mAh g -1 at 2 C) can still be retained.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Sound speed measurements in lithium fluoride single crystals shock compressed to 168 GPa along [100]

The shock wave response of [100] lithium fluoride (LiF) single crystals at high stresses is of long-standing interest due to their extensive use as optical windows in dynamic compression experiments. The report of melting in shock compressed LiF single crystals between 134 GPa and 152 GPa – based on a single sound speed datum [J. Appl. Phys. 117, 045901 (2015)] – was surprising because good optical transmission was previously demonstrated in LiF shock compressed to ~200 GPa [J. Appl. Phys. 116, 033515 (2014)]. To address these apparent differences, we report on plate impact experiments on [100] LiF single crystals shock compressed to 168 GPa. Wave profiles were measured using laser interferometry to determine Hugoniot states and longitudinal sound speeds in shock compressed LiF. The measured Hugoniot states are in good agreement with those measured in previous studies. However, the measured sound speeds presented here show no evidence of melting up to 168 GPa. In particular, the abrupt drop reported previously in sound speed at 152 GPa was not observed in the present work. Furthermore, our results establish a lower bound of 168 GPa for the onset of melting in shock compressed LiF single crystals.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Refractive index of lithium fluoride at high dynamic stresses

Alkali halides are prototypical ionic solids whose refractive index is a fundamental property related to their lattice structure and ionic polarizability. In particular, lithium fluoride (LiF) has the largest band gap of any known transparent material and maintains transparency at high pressures, making it well suited for use as an optical window in dynamic compression experiments. While empirical fits to the measured density dependence of the refractive index have been provided, a model that is valid over the entire pressure range of experiments and based on a polarization-based theoretical description is lacking. We present a refractive index model for dynamically compressed LiF based on the Lorentz-Lorenz equation, where the molecular polarizability is determined using a single oscillator model with a strain polarizability parameter Λ=0.73. Here, we show that our modeling approach provides an excellent match to the LiF refractive index data for both shock and ramp compression experiments to 900 GPa (density compression greater than threefold). Additionally, updated fits are provided to determine the refractive index correction for LiF windows used in dynamic compression experiments.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Safeguards for the Lithium Fluoride Thorium Reactor: A Preliminary Nuclear Material Control and Accounting Assessment

This report was prepared by Oak Ridge National Laboratory (ORNL) for Flibe Energy Inc. (FEI), a US-based advanced reactor company founded in 2011 and headquartered in Huntsville, Alabama. FEI is developing the lithium-fluoride thorium reactor (LFTR), which is a modern two-fluid molten salt reactor (MSR) design operating on a thorium/ 233 U fuel cycle. FEI intends for LFTR to become a self-sustaining clean energy source that can create or breed its own fuel from thorium. Each LFTR is intended to breed enough fissile material to compensate for the amount it consumes. Consequently it would not require fissile replenishment during its operational lifetime. This self-sustaining nature would eliminate the need for uranium enrichment infrastructure to support LFTRs after the first generation.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Shock-induced melting of [100] lithium fluoride: Sound speed and Hugoniot measurements to 230 GPa

Although [100] lithium flouride (LiF) is the most widely used optical window material in dynamic compression experiments, its high stress (>100 GPa) shock compression response, including melting, is not well understood. To address this need, we measured wave profiles in plate impact experiments to determine the Hugoniot states and longitudinal sound speeds in [100] LiF crystals shock compressed to 231 GPa. The measured peak states are fitted well by a linear shock velocity-particle velocity relation, providing an accurate determination of the LiF Hugoniot curve to significantly higher stresses than previous experiments. The longitudinal sound speeds show a near linear increase with density compression to 182 GPa. Between 182 GPa and 195 GPa, the sound speed and the longitudinal modulus decrease abruptly, due to shock-induced melting. The increasing sound speeds and moduli at higher stresses suggest that shock compressed LiF is fully liquid at 195 GPa and above, allowing determination of the Gruneisen parameter for liquid LiF. Here, the melt stress determined here differs from that predicted by current multiphase equations of state for LiF. Our results provide important insight into the high stress solid and liquid states of shock compressed LiF and point to the need for an improved multiphase equation of state at high pressures and high temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Interfacial Speciation Determines Interfacial Chemistry: X-ray-Induced Lithium Fluoride Formation from Water-in-salt Electrolytes on Solid Surfaces

Using synchrotron X-rays the LiTFSI/H 2 O electrolyte interfacial decomposition pathways in the „water-in-salt“ and „salt-in-water“ regimes are investigated. The resultant photoelectron-induced reduction was revealed to be concentration-dependent interfacial chemistry that only occurs among closely contact ion-pairs, which constitutes the rationale behind the „water-in-salt“ concept.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2017

First-principles simulations of warm dense lithium fluoride

Here we perform first-principles path integral Monte Carlo (PIMC) and density functional theory molecular dynamics (DFT-MD) calculations to explore warm dense matter states of LiF. Our simulations cover a wide density-temperature range of 2.08–15.70g cm -3 and 10 4 –10 9 K. Since PIMC and DFT-MD accurately treat effects of atomic shell structure, we find a pronounced compression maximum and a shoulder on the principal Hugoniot curve attributed to K-shell and L-shell ionization. The results provide a benchmark for widely used EOS tables, such as SESAME, LEOS, and models. In addition, we compute pair-correlation functions that reveal an evolving plasma structure and ionization process that is driven by thermal and pressure ionization. Finally, we compute electronic density of states of liquid LiF from DFT-MD simulations and find that the electronic gap can remain open with increasing density and temperature to at least 15.7 g cm -3 .

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗