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DOE OSTI2022

In-situ synthesis of porous metal fluoride@carbon composite via simultaneous etching/fluorination enabled superior Li storage performance

Transition metal fluorides as Li-free conversion-type cathode materials have high theoretical specific capacities, however, their preparation strategy, sluggish electrochemical kinetic and poor cyclability have impeded their wide adoption in lithium-ion batteries. Herein, a facile in-situ synthesis of porous metal-fluoride-carbon composites is accomplished via simultaneous polytetrafluorethylene-based hard template etching and metal fluorination. This not only facilitates fast electron transfer and lithium-ion diffusion kinetics, but also buffers severe volume fluctuation during lithiation/delithation and enables the formation of a uniform and thin Li 2 CO 3 /LiF-rich cathode-electrolyte interphase. Here, as a proof of concept, the as-prepared porous FeF 3 @C (p-FeF 3 @C) indeed exhibits a high specific capacity of 230 mAh g -1 at 0.1 C together with an excellent capacity retention of 92.5% at 1 C for 200-cycles. Moreover, the practicality of the strategy is demonstrated by the superb electrochemical performance of the full-cells coupled with pre-lithiated graphite anodes. Therefore, the proposed novel synthetic strategy will enlighten the future design of high-performance metal-fluoride-carbon composites with porous structure for energy storage applications.

25 ENERGY STORAGE↗

DOE OSTI2020

Tritium generation, release, and retention from in-core fluoride salt irradiations

Further understanding of tritium transport mechanisms in the combined molten fluoride salt and graphite environment is necessary for the design and licensing of a Fluoride-Salt-Cooled High-Temperature Reactor (FHR). The three in-core fluoride salt irradiations completed at the Massachusetts Institute of Technology Reactor (MITR) are a useful parallel for studying transport phenomena expected in a FHR environment. During the irradiations, evolution of tritium from the flibe salt was monitored and compared to the calculated total generation rate. A difference of 22 ± 10% between the integrated calculated tritium generation rate and the total release was measured for the third MITR irradiation (FS-3). The fraction of tritium which was not released from the salt could be explained by tritium retention in graphite. Additionally, for post irradiation examination, a thermal desorption furnace was used to heat nuclear graphite samples in order to release and measure retained tritium. The desorption analysis in this work utilized seven subsections of graphite from the second salt irradiation (FS-2); three from a disc of IG-110U and four from ARB matrix graphite. Observed desorption versus temperature as well as total tritium content in the samples after irradiation indicate that the graphites were not volumetrically saturated with tritium, but rather tritium retention was likely limited to the near-surface region. Measurements of the samples resulted in 2.90 ± 0.29 μCi/mm 2 of tritium retained by IG-110U and 1.83 ± 0.31 μCi/mm 2 for ARB during the 300 h FS-2 in-core irradiation. Based on the desorption measurements, the estimated total tritium retention in graphite from the FS-2 samples is consistent with the tritium release measurements from the FS-3 experiment.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

DOE OSTI2024

Entropy-Stabilized Multication Fluorides as a Conversion-Type Cathode for Li-Ion Batteries–Impact of Element Selection

Metal fluorides (e.g., FeF 2 and FeF 3 ) have received attention as conversion-type cathode materials for Li-ion batteries due to their higher theoretical capacity compared to that of common intercalation materials. However, their practical use has been hindered by low round-trip efficiency, voltage hysteresis, and capacity fading. Cation substitution has been proposed to address these challenges, and recent advancements in battery performance involve the introduction of entropy stabilization in an attempt to facilitate reversible conversion reactions by increasing configurational entropy. Building on this concept, high entropy fluorides with five cations were synthesized by using a simple mechanochemical route. In order to examine the impact of element selection, Co 0.2 Cu 0.2 Ni 0.2 Zn 0.2 Fe 0.2 F 2 (HEF-Fe) was compared with Co 0.2 Cu 0.2 Ni 0.2 Zn 0.2 Mg 0.2 F 2 (HEF-Mg), replacing electrochemically inactive Mg with Fe as an active participant in the conversion reaction. Combining electrochemical measurements with first-principles calculations, high-resolution electron microscopy, and synchrotron X-ray analysis, HEFs’ battery performances and conversion reaction mechanisms were investigated in detail. The results highlighted that replacement of Mg with Fe was beneficial, with enhanced capacity, rate capability, and surface stability. In addition, it was found that HEF-Fe showed similar cycle stability without an electrochemically inactive element. In conclusion, these findings provide valuable insights for the design of high entropy multielement fluorides for improved Li-ion battery performance.

25 ENERGY STORAGE↗

DOE OSTI2024

Formation and Microwave Losses of Hydrides in Superconducting Niobium Thin Films Resulting from Fluoride Chemical Processing

Abstract Superconducting niobium (Nb) thin films have recently attracted significant attention due to their utility for quantum information technologies. In the processing of Nb thin films, fluoride‐based chemical etchants are commonly used to remove surface oxides that are known to affect superconducting quantum devices adversely. However, these same etchants can also introduce hydrogen to form Nb hydrides, potentially negatively impacting microwave loss performance. Here, comprehensive materials characterization of Nb hydrides formed in Nb thin films as a function of fluoride chemical treatments is presented. In particular, secondary‐ion mass spectrometry, X‐ray scattering, and transmission electron microscopy reveal the spatial distribution and phase transformation of Nb hydrides. The rate of hydride formation is determined by the fluoride solution acidity and the etch rate of Nb 2 O 5, which acts as a diffusion barrier for hydrogen into Nb. The resulting Nb hydrides are detrimental to Nb superconducting properties and lead to increased power‐independent microwave loss in coplanar waveguide resonators. However, Nb hydrides do not correlate with two‐level system loss or device aging mechanisms. Overall, this work provides insight into the formation of Nb hydrides and their role in microwave loss, thus guiding ongoing efforts to maximize coherence time in superconducting quantum devices.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Effect of the filler morphology on the crystallization behavior and dielectric properties of the polyvinylidene fluoride‐based composite

Abstract Ceramic/polymer composites can be chemically stable, mechanically strong, and flexible, which make them candidates for electric devices, such as pressure or temperature sensors, energy storage or harvesting devices, actuators, and so forth. Depending on the application, various electrical properties are of importance. Polymers usually have low dielectric permittivity, but increased dielectric permittivity can be achieved by the addition of the ceramic fillers with high dielectric constant. With the aim to enhance dielectric properties of the composite without loss of flexibility, 5 wt% of BaTiO 3 ‐Fe 2 O 3 powder was added into a polyvinylidene fluoride matrix. The powder was prepared by different synthesis conditions to produce core/shell structures. The effect of the phase composition and morphology of the BaTiO 3 ‐Fe 2 O 3 core/shell filler on the structure and lattice dynamics of the polymer composites was investigated. Based on the results of the thermal analysis, various parameters of ceramic/polymer composites were determined. Differences in the phase composition and morphology of the filler have an influence on the formation of various polyvinylidene fluoride allomorphs and the degree of crystallinity. Furthermore, the dielectric performances of pure polyvinylidene fluoride and the polymer/ceramic composites were measured.

Polymer Science↗

DOE OSTI2023

Targeting Oxide Concentration in Tantalum Oxide-Fluoride Anions

The design of both molecular and non-molecular solid materials with specific properties fundamentally relies on the controlled synthesis of crystals with desired functional groups, bonding motifs, polarity, chirality, and more. To this end, fluoride and oxide-fluoride anions have been utilized as basic building units (BBUs) in the synthesis of noncentrosymmetric racemic materials for their ability to create polar axes that facilitate the breaking of an inversion center as demonstrated in a series of compounds with [MF6]2- anions (M = Ti, Zr, Hf). Targeting an analog with a [TaOF5]2- anion, the phase space of (CuO, Ta2O5)/bpy/HF(aq)/H2O (bpy = 2,2′-bipyridine) was investigated and three new compounds with Cu-bpy cations and Ta-fluoride or Ta-oxyfluoride anions were synthesized: [Cu(bpy)2][TaF6], [Cu(bpy)2][Ta2OF10], and [Cu(bpy)F(H2O)2]2[TaF7]∙H2O with the anions [TaF6]-, [Ta2OF10]2-, and [TaF7]2-, respectively. The formation of these anions was found to be a product of both the concentration of hydrofluoric acid in solution and the ratio of metal-oxide starting materials to ligand. This work contributes to the understanding of mixed anion formation in the solid state.

Kamp, Kendall R.↗

DOE OSTI2022

Excitonic Effects in X-ray Absorption Spectra of Fluoride Salts and Their Surfaces

Given their natural abundance and thermodynamic stability, fluoride salts may appear as evolving components of electrochemical interfaces in Li-ion batteries and emergent multivalent ion cells. This is due to the practice of employing electrolytes with fluorine-containing species (salt, solvent, or additives) that electrochemically decompose and deposit on the electrodes. Operando X-ray absorption spectroscopy (XAS) can probe the electrode–electrolyte interface with a single-digit nanometer depth resolution and offers a wealth of insights into the evolution and Coulombic efficiency or degradation of prototype cells, provided that the spectra can be reliably interpreted in terms of local oxidation state, atomic coordination, and electronic structure about the excited atoms. Here we explore fluorine K-edge XAS of mono- (Li, Na, and K) and di-valent (Mg, Ca, and Zn) fluoride salts from a theoretical standpoint and discover a surprising level of detailed electronic structure information about these materials despite the relatively predictable oxidation state and ionicity of the fluoride anion and the metal cation. Utilizing a recently developed many-body approach based on the ΔSCF method, we calculate the XAS using density functional theory and experimental spectral profiles are well reproduced despite some experimental discrepancies in energy alignment within the literature, which we can correct for in our simulations. We outline a general methodology to explain shifts in the main XAS peak energies in terms of a simple exciton model and explain line-shape differences resulting from the mixing of core-excited states with metal d character (for K and Ca specifically). Given ultimate applications to evolving interfaces, some understanding of the role of surfaces and their terminations in defining new spectral features is provided to indicate the sensitivity of such measurements to changes in interfacial chemistry.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2024

Chemically Driven Multistep Crystallization in the Synthesis of Sodium Yttrium Fluoride Via a Porous, Electrochemically Active Intermediate

Two-step crystallization mechanisms based on liquid–liquid phase separations followed by crystallization are commonly observed both in the laboratory and in nature. While this pathway quite often occurs as a result of a chemical reaction, the subsequent nucleation and growth are often considered as separate, discrete events from the reaction itself. We show this mechanism in the aqueous synthesis sodium yttrium fluoride, but by using a combination of experimental techniques and computational modeling, we show an additional step of solid-state chemical diffusion that is essential to the nucleation mechanism. In this system, we observe at least four distinct steps in the crystallization process, including (1) the segregation of aqueous ions into a dense liquid phase, (2) the formation of a metastable amorphous aggregate, (3) the continuous, gradual solid-state diffusion of sodium and fluoride ions into the amorphous aggregate toward a NaYF4 stoichiometry, and (4) the crystallization of a stable cubic sodium yttrium fluoride phase. Unlike previous descriptions of nucleation and growth, we find that the stoichiometry of the final solid phase evolves throughout the crystallization process rather than being determined at the time of the initial separation from solution. Further, this emphasizes that the chemical reaction cannot be assumed to be a separate event from the phase separation and growth, especially in compounds with variable stoichiometry. We also find that the amorphous aggregate that forms prior to the ion incorporation step adopts a porous, gel-like structure, which we isolated and showed to be electrochemically active, allowing for its potential use as a battery anode in lithium and sodium ion batteries, among other potential applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2025

Effect of Fluoride Anions on Nd(III) Electrode Processes and Nd Metal Recovery in LiCl–KCl–NdCl 3

Here, this work investigated the impact of fluoride anions on Nd metal recovery in LiCl–KCl–NdCl 3 electrolytes by introducing LiF at a molar F/Nd ratio of 9 at 773 K. The voltammetric measurements confirmed that the fluoride ions facilitated single-step Nd(III)/Nd reduction by promoting the stability of the Nd(III) state compared to two-step reduction (Nd(III)/Nd(II) and Nd(II)/Nd) in all-chloride electrolytes. The stabilized Nd(III) state in the LiF-containing electrolyte effectively suppressed partial Nd(III)/Nd(II) reduction and the back-dissolution of Nd metal via comproportionation. By suppressing these reactions, high round-trip Coulombic efficiencies of 77–86% were achieved in the LiF-containing electrolyte during selective Nd deposition–removal cycles compared to 53–59% in all-chloride electrolytes. The Faradaic yield for Nd metal recovery was estimated at 38.6% in the LiF-containing electrolyte following long-term electrolysis, more than three times higher than 11.3% in all-chloride electrolytes. These results confirm the beneficial effect of fluoride ions on Nd metal recovery in low-melting chloride-based electrolytes, promising efficient Nd recovery at low temperatures.

11 - NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2024

Enhanced superconducting qubit performance through ammonium fluoride etch

The performance of superconducting qubits is often limited by dissipation and two-level systems (TLS) losses. The dominant sources of these losses are believed to originate from amorphous materials and defects at interfaces and surfaces, likely as a result of fabrication processes or ambient exposure. Here, we explore a novel wet chemical surface treatment at the Josephson junction-substrate and the substrate-air interfaces by replacing a buffered oxide etch (BOE) cleaning process with one that uses hydrofluoric acid followed by aqueous ammonium fluoride. We show that the ammonium fluoride etch process results in a statistically significant improvement in median $\text{T}_1$ by $\sim22\%$ (p = 0.002), and a reduction in the number of strongly-coupled TLS in the tunable frequency range. Microwave resonator measurements on samples treated with the ammonium fluoride etch after niobium deposition and etching also show $\sim33\%$ lower TLS-induced loss tangent compared to the BOE treated samples. As the chemical treatment primarily modifies the Josephson junction-substrate interface and substrate-air interface, we perform targeted chemical and structural characterizations to examine materials differences at these interfaces and identify multiple microscopic changes that could contribute to decreased TLS losses.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Enhanced Hanford High-Fluoride Waste Glass Property Data Development: Phase 1

This study focused on investigating the effects of fluorine concentration on simulated high-level waste glass properties to eventually establish a fluorine limit (as a single-component or multiple-component constraint) for glass formulations for high-fluoride Hanford wastes. This is a first step to provide data to understand the impacts of changing flowsheets on the mission duration and extent. A test matrix of 20 high-fluoride glasses was generated, and the chemical compositions were measured. The following properties were measured and tested against current model predictions: crystal formation after centerline canister cooling, crystallinity as a function of temperature, density, viscosity, electrical conductivity, toxic leaching characteristics using the toxicity characteristic leach profile (TCLP), product consistency using the product consistency test (PCT), and SO 3 solubility. Overall, current models failed to adequately predict most of the properties, possibly due to differences in compositional space used to generate the models and the current test matrix. Additional work is needed to more accurately assess the impacts of high-fluoride wastes on Hanford processing, including additional data collection over a broader composition region and model development for the key models of interest such as PCT and TCLP.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2025

Completion of Transport Property Measurements on Multiple Actinide Fluoride Mixtures

One of the missions of the US Department of Energy’s Office of Nuclear Energy (DOE-NE) Molten Salt Reactor (MSR) Campaign under the Advanced Reactor Technology program has been to experimentally measure thermophysical properties of MSR-relevent salt systems, with the intent of supporting the development of the Molten Salt Thermal Properties Database (MSTDB). This database is jointly funded by the DOE-NE Nuclear Energy Advanced Modeling and Simulation Program and the MSR Campaign. Multiple DOE national laboratories, including Oak Ridge National Laboratory (ORNL), have been conducting measurements of thermophysical properties to support MSTDB development and provide MSR developers with access to new data that has been measured using modern methodologies and more advanced sample characterization techniques. These data may either fill gaps in the database or provide updated higher quality data to replace legacy data. Researchers at ORNL have recognized significant gaps in the transport property data of actinide-bearing fluoride salt systems of MSR industry interest. Moreover, for the data present in MSTDB in this category, the uncertainty margins are generally high, leading to questionability in our current understanding of the thermophysical characterization of actinide fluoride mixtures. As such, the focus of this study has been to generate new transport property data of actinide fluoride mixtures that are of immediate interest to MSR developers. Specifically, the mixtures NaF-UF 4 (78 - 22 mol%) and NaF-KF-UF 4 (57-16.04-26.91 mol%) have been studied—NaF-UF 4 for thermal conductivity and viscosity and NaF-KF-UF 4 for viscosity. Thermal conductivity measurements have been conducted with a variable gap apparatus, whereas viscosity has been measured with a rolling ball viscometer. Methodological and calibration details are provided for both measurement processes, along with measurement system updates that have enabled easier manufacturing of components and fewer challenges associated with conducting the measurements themselves. The resultant data collected for NaF-UF 4 (78–22 mol%) and NaF-KF-UF 4 (57-16.04-26.91 mol%) have been compared with relevant mixture data within the thermophysical arm of the MSTDB (MSTDB-TP).

22 GENERAL STUDIES OF NUCLEAR REACTORS↗

DOE OSTI2026

Best Methods for Fluoride Fuel Salt Dissolution and Digestion

This report serves as the deliverable for Milestone M4FT-26AN080502015 (Report on methodology for elemental/isotopic analysis of fluoride fuel salts). The review within this document is a summary of the current literature identified by Argonne regarding fluoride salt dissolution and digestion methods and provides guidance on selecting optimal fluoride dissolution and digestion methods for future fuel salt qualification studies. Methods are compared based on completeness of digestion, chemical hazards, and tradeoffs such as equipment needs or potential to introduce impurities. Recommendations are provided for best dissolution and digestion methods for uranium- and thorium-bearing salts, and ideas for key future experiments are described.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2022

Enabling Conversion-Type Iron Fluoride Cathode by Halide-Based Solid Electrolyte

The practical application of low-cost and energy-dense iron fluoride cathodes has been hindered by the first cycle electrochemical irreversibility, cycling instability, and large voltage hysteresis. Here, we report that these challenges may be overcome by the utilization of halide-based solid electrolytes (SEs). The excellent electrochemical stability of halide-based SEs enables a complete conversion and deconversion of FeF 2 which cannot be achieved with sulfide-based SEs. Due to restricted and reversible decomposition of SE, prevention of Fe dissolution, mechanical confinement of active material, as well as improved electrode kinetics, solid-state FeF 2 cathode with halide-based SE demonstrated superior electrochemical performance compared with FeF 2 electrodes in liquid electrolytes, with a high 1st cycle coulombic efficiency (~100 %), high specific capacity (~600 mAh/g), long cycle life (>100 cycles) and high-rate performance (up to 2C). In conclusion, our results suggest solidifying the batteries may be a viable approach to addressing the long-standing key challenges of iron fluoride cathodes.

25 ENERGY STORAGE↗

DOE OSTI2020

Calcium fluoride as a dominating matrix for quantitative analysis by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS): A feasibility study

Here, calcium fluoride formed by the reaction between ammonium bifluoride and calcium chloride was investigated as a dominating matrix for quantitative analysis by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Transformation from a solid sample to the calcium fluoride-based matrix permitted quantitative analysis based on calibration standards made from elemental standards. A low abundance stable calcium isotope, i.e. 44 Ca + , was monitored as the internal standard for quantitative analysis by LA-ICP-MS. Correlation coefficient factors for multiple elements were obtained with values over 0.999. The results for multiple elements in a certified reference material of soil (NIST SRM 2710a) agreed with the certified values in the range of expanded uncertainty, indicating the present method was valid for quantitation of elements in solid samples.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Investigation of $\gamma$-irradiated polyvinylidene fluoride and its acute toxicity

Polyvinylidene fluoride (PVDF) is an industrial polymer with many applications. The EPR spectrum of polyvinylidene fluoride (PVDF) irradiated by γ-rays at low temperature (-196°C) provides evidence for the presence of radicals formed by loss of a fluorine atom from PVDF, and polyenyl radicals. Polyenyl radicals dominate in the polymer irradiated at room temperature. Peroxide radicals formed as a result of oxidation of primary free radicals by atmospheric oxygen are observed in the EPR spectrum of a polymer irradiated in air, or when air is introduced to a polymer irradiated in a vacuum. Carbonization and oxidation of γ-irradiated PVDF were observed in the XPS spectrum. A model for polymer degradation based on correlated G3(MP2) molecular orbital theory electronic structure calculations is described in this report. The presence of HF in the products and a low yield of products with the composition CxFyHz indicate the absence of noticeable thermal destruction of the main polymer chain upon heating to 220°C of both the initial and γ-irradiated PVDF. Although any HF released during the PVDF dehydrofluorination would be toxic, a study of the acute toxicity of γ-irradiated PVDF showed that the polymer does not exhibit toxicity after a single intragastric route of administration to mice.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2020

Direct drive with the argon fluoride laser as a path to high fusion gain with sub-megajoule laser energy

Argon fluoride (ArF) is currently the shortest wavelength laser that can credibly scale to the energy and power required for high gain inertial fusion. ArF's deep ultraviolet light and capability to provide much wider bandwidth than other contemporary inertial confinement fusion (ICF) laser drivers would drastically improve the laser target coupling efficiency and enable substantially higher pressures to drive an implosion. Our radiation hydrodynamics simulations indicate gains greater than 100 are feasible with a sub-megajoule ArF driver. Our laser kinetics simulations indicate that the electron beam-pumped ArF laser can have intrinsic efficiencies of more than 16%, versus about 12% for the next most efficient krypton fluoride excimer laser. We expect at least 10% ‘wall plug' efficiency for delivering ArF light to target should be achievable using solid-state pulsed power and efficient electron beam transport to the laser gas that was demonstrated with the U.S. Naval Research Laboratory's Electra facility. These advantages could enable the development of modest size and lower cost fusion power plant modules. This would drastically change the present view on inertial fusion energy as being too expensive and the power plant size too large.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

DOE OSTI2020

Carburization of metals by a chemical mechanism of carbon transport through molten fluoride salts

Carburization of structural alloys used in Fluoride Cooled High Temperature Reactors (FHR) can result from the interaction between the metal and graphite components and cause changes in alloy properties. However, carburization requires transport of carbon from graphite to alloy surfaces through the molten fluoride coolant. This work introduces an alternative to previously proposed carbon transport mechanisms. The new mechanism is based on the generation of carbonate ions (CO 3 2- ) by oxide impurities in the salt reacting with graphite. CO 3 2- is then reduced on metal surfaces to deposit carbon. This work demonstrates the reduction of dissolved CO 3 2- on pure Fe, Ni, Cr, Mo, and W surfaces without an applied potential in molten FLiNaK at 700 °C. Finally, we also demonstrate that the interaction between oxide and graphite in molten FLiNaK media produces CO 3 2- .

36 MATERIALS SCIENCE↗