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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

De novo fabrication of multi-heteroatom-doped carbonaceous materials via an in situ doping strategy

Finding a succinct strategy to fabricate multi-heteroatom-doped nanoporous carbonaceous materials is a long-term challenge and highly desired research topic. The key to success is the rational design of easy to obtain and functionalized precursors. Herein, de novo fabrication of carbonaceous materials doped with multiple heteroatoms namely boron, nitrogen, oxygen, fluorine, and sulfur was achieved via a one-step in situ doping procedure using task-specific ionic liquids (TSILs) as precursors. Our strategy hinges on the adoption of particularly designed TSILs with structures functionalized with (1) boron source-containing anions, (2) imidazolium functionalities as the carbon and nitrogen source, (3) nitrile groups capable of trimerization during the heating process, and (4) bis(trifluoromethanesulphonyl)imide and related anions performing as the source of heteroatoms (i.e., fluorine, nitrogen, sulfur, and oxygen) and porogens. The unique structures of the as-prepared TSILs make them qualified precursors for the production of multi-heteroatom-doped carbonaceous materials through simple thermal treatment, with surface areas up to 1021 m 2 g -1 . The introduction of multiple heteroatoms provides the carbonaceous materials with efficient adsorption performance for the capture of hazardous anionic pollutants, dyes, and neutral organic molecules. This finding expands the versatility of TSILs with multi-functionalized architectures, delivering nanoporous materials with wide applications.

36 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↗
DOE OSTI2021

Potential energy profile for the Cl + (H 2 O) 3 → HCl + (H 2 O) 2 OH reaction. A CCSD(T) study

Four different reaction pathways are initially located for the reaction of Cl atom plus water trimer Cl + (H 2 O) 3 → HCl + (H 2 O) 2 OH using a standard DFT method. As found for the analogous fluorine reaction, the geometrical and energetic results for the four chlorine pathways are closely related. However, the energetics for the Cl reaction are very different from those for fluorine. Here in this paper, we investigate the lowest-energy chlorine pathway using the “gold standard” CCSD(T) method in conjunction with correlation-consistent basis sets up to cc-pVQZ. Structurally, the stationary points for the water trimer reaction Cl + (H 2 O) 3 may be compared to those for the water monomer reaction Cl + H 2 O and water dimer reaction Cl + (H 2 O) 2 . Based on the CCSD(T) energies, the title reaction is endothermic by 19.3 kcal mol -1 , with a classical barrier height of 16.7 kcal mol -1 between the reactants and the exit complex. There is no barrier for the reverse reaction. The Cl … (H 2 O) 3 entrance complex lies 5.3 kcal mol -1 below the separated reactants. The HCl … (H 2 O) 2 OH exit complex is bound by 8.6 kcal mol -1 relative to the separated products. The Cl + (H 2 O) 3 reaction is somewhat similar to the analogous Cl + (H 2 O) 2 reaction, but qualitatively different from the Cl + H 2 O reaction. It is reasonable to expect that the reactions between the chlorine atom and larger water clusters may be similar to the Cl + (H 2 O) 3 reaction. The potential energy profile for the Cl + (H 2 O) 3 reaction is radically different from that for the valence isoelectronic F + (H 2 O) 3 system, which may be related to the different bond energies between HCl and HF.

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

Molecular engineering of fluoroether electrolytes for lithium metal batteries

Fluoroether solvents are promising electrolyte candidates for high-energy-density lithium metal batteries, where high ionic conductivity and oxidative stability are important metrics for design of new systems. Recent experiments have shown that these performance metrics, particularly stability, can be tuned by changing the fraction of ether and fluorine content. However, little is known about how different molecular architectures influence the underlying ion transport mechanisms and conductivity. Here, we use all-atom molecular dynamics simulations to elucidate the ion transport and solvation characteristics of fluoroether chains of varying length, and having different ether segment and fluorine terminal group contents. The design rules that emerge from this effort are that solvent size determines lithium-ion transport kinetics, solvation structure, and solvation energy. In particular, the mechanism for lithium-ion transport is found to shift from ion hopping between solvation sites located in different fluoroether chains in short-chain solvents, to ion–solvent co-diffusion in long-chain solvents, indicating that an optimum exists for molecules of intermediate length, where hopping is possible but solvent diffusion is fast. Consistent with these findings, our experimental measurements reveal a non-monotonic behavior of the effects of solvent size on lithium-ion conductivity, with a maximum occurring for medium-length solvent chains. Finally, a key design principle for achieving high ionic conductivity is that a trade-off is required between relying on shorter fluoroether chains having high self-diffusivity, and relying on longer chains that increase the stability of local solvation shells.

25 ENERGY STORAGE↗
DOE OSTI2022

Crystal engineering of heterocyclic arylene(ethynylene) oligomers through programmed aromatic stacking

Conjugated oligomers and polymers consisting of aromatic heterocycles are examples of next-generation organic electronic materials. However, control and optimization of the self-assembly of these materials in the solid-state, which is a crucial parameter for high efficiency performance, remains an unsolved challenge in materials development. In this work, we provide valuable insight into aromatic stacking interactions between fluorinated arene rings (ArF) and heterocycles with different electronic character (Het), and elaborate on the prospect of using these interactions to control the solid-state configurations of three-ring phenyleneethynylene oligomers (PEs). Oligomers possessing heterocycles typically thought of as electron-rich (ER) show blue-shifted optical spectra in the solid-state, while those incorporating heterocycles typically thought of us electron deficient (ED) show red-shifted solid-state optical spectra. Crystal structures show ArF-Het stacking interactions between the fluorinated side-chains and ER units, which twist the backbone out of planarity and prevent chromophore aggregation. Further, the interactions are absent in ED oligomers, highlighting cofacial incompatibility between ArF rings and ED units. A combination of TD-DFT computations and novel heterocycle descriptors reinforce our assignment of the oligomers as ED or ER, while exhaustive conformer analysis shows ArF-Het stacking interactions are a significant contributor to compound stability. Overall, this work describes the importance of heterocycle electronics in conformational control in the solid state, understanding of which can be a valuable asset in the development of novel optoelectronic materials.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Tuning charge carrier dynamics through spacer cation functionalization in layered halide perovskites: an ab initio quantum dynamics study

Dion–Jacobson (DJ) phase two-dimensional (2D) hybrid halide perovskites are promising for environmentally stable optoelectronic device applications due to their attractive photophysical properties, including long charge carrier lifetime and partially suppressed non-radiative losses. However, the atomistic details of the structure–property relationship are severely limited, which substantially restricts the strategic materials designed for these layered halide perovskites (LHPs). Here, we combine nonadiabatic molecular dynamics and time-domain density functional theory to understand the effects of spacer cation functionalization on the ground and excited-state charge carrier dynamics in DJ phase LHPs. Our in-depth study reveals that the fluorination of spacer cations considerably restricts the thermal motions of LHPs at ambient conditions. The compact structure weakens the overall electron–phonon interactions and reduces the thermal fluctuations of the band edges in real-time. These dynamic modifications partially mitigate the non-radiative recombination, prolonging the lifetime of photogenerated charge carriers. The suppressed carrier loss mechanism strongly suggests that the fluorinated spacer cation-based LHPs would exhibit enhanced performance as optoelectronic materials. These systematic simulations of excited state carrier dynamics elaborate that chemically viable functionalization of the spacer cations is a robust approach to improve the photophysical properties of 2D halide perovskites strategically. These insights also guide us to propose a few potential strategies to design highly beneficial spacer cations of LHPs that can be introduced in next-generation optoelectronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Structural regulation-induced Li-electron disentanglement for stabilized oxygen redox of Li-excess disordered rock-salt cathode materials

Since the discovery of its electrochemical activity, Li-excess disordered rock-salt (DRX) cathode material has received worldwide attention as it sets up a new way to exploit oxygen redox beyond the conventional layered structure with late-3d transition metals. However, the intricate structure-function relationship in the disordered lattice of the DRX material fogs the researcher's lens on the underlying redox mechanisms. Here, in this study, we employ a synergistic approach combining neutron total scattering with reverse Monte Carlo modeling and density functional theory calculations to unravel the landscape of oxygen redox reactions in DRX. Redox activities are evaluated in diverse oxygen clusters (OLi x TM 6-x ) and the spatial distribution of these clusters in the model DRX structure (Li 1.16 Ti 0.37 Ni 0.37 Nb 0.1 O 2 and Li 1.2 Ti 0.35 Ni 0.35 Nb 0.1 O 1.8 F 0.2 ) is explicitly determined. The results unveil that by regulating the short-range ordering between cations, fluorine atoms can effectively decouple the location of Li extraction and electron depletion. Such disentanglement between the Li reservoir and electron reservoir in the DRX lattice could play a pivotal role in protecting the oxidized oxygen and preserving the lattice framework during cycling. Through a tentatively designed non-fluorinated DRX oxide realizing similar Li-electron decoupling, an obvious enhancement of the cycling capability can be achieved without compromising the capacity release.

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

Surface acoustic waves and lattice vibrations in two-dimensional Ti 3 ⁢C 2 ⁢𝑇 𝑥 (𝑇 =O, F) MXene films

We investigated surface acoustic wave (SAW) propagation and lattice vibrations in two-dimensional (2D) titanium carbide (Ti 3 ⁢C 2 ⁢𝑇 x ) MXene films as a function of surface termination and layer stacking, using atomistic simulations. We found that SAW propagation velocity is highly sensitive to both single-layer properties and interlayer bonding. Surface terminations significantly modulate wave behavior, with oxygen and fluorine terminations producing distinct effects on wave propagation, with oxygen-terminated monolayers exhibiting 20% higher wave speeds than fluorine counterparts due to strengthened intralayer bonds. Key observations include the transition from one to two layers causing wave speed variations, and the development of interlayer modes that generate more dispersed lattice vibrations. As the film layer thickness increases, SAW propagation becomes predominantly confined to the upper surface, with coherence of vibrational modes diminishing in multilayer structures. These findings suggest MXene terminations and layer stacking are crucial parameters for controlling SAW behavior, offering promising avenues for novel acoustic wave device applications.

2-dimensional systems↗
DOE OSTI2022

Density matrix renormalization group description of the island of inversion isotopes F 28 – 33

Recent experiments have confirmed that the neutron-rich isotopes 28,29 F belong to the so-called island of inversion (IOI), a region of the nuclear chart around Z = 10 and N = 20 where nuclear structure deviates from the standard shell model predictions due to deformation and continuum effects. However, while the general principles leading to the IOI are relatively well understood, the details of the low-lying structure of the exotic fluorine isotopes 28–33 F are basically unknown. In this study, we perform large-scale shell model calculations including continuum states to investigate the properties of the neutron-rich isotopes 25–33 F, from a core of 24 O and using an effective two-body interaction with a small number of adjustable parameters in the central and tensor channels. We develop two models adjusted on experimentally confirmed states in 25,26 O and 25–27 F based on different assumptions concerning the positions of the neutron 0d 3/2 and 1p 3/2 shells, and solve the many-body problem using the density matrix renormalization group (DMRG) method for open quantum systems in an sd–fp model space. We obtain the first detailed spectroscopy of 25–33F in the continuum and show how the interplay between continuum effects and deformation explains the recent data on 28,29 F. Several deformed one- and two-neutron halo states are predicted in 29,31 F, and we provide some information about the possible structure of the heaviest fluorine isotopes. We also suggest several experimental studies of interest to constraint models and test the present predictions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Phase transitions and potential ferroelectricity in noncentrosymmetric KNaNbOF 5

Increasing the number of known ferroelectrics requires expanding the chemical design space and mechanisms producing ferroelectricity. To that end, we examine the displacive, noncentrosymmetric-to-centrosymmetric phase transition in the oxyfluoride KNaNbOF 5 using ab initio calculations and Landau theory. Here we predict an intermediate Pnma phase occurs in the transition from the known low- and high-temperature phases, Pna2 1 and Cmcm, respectively, which we subsequently confirm using high-resolution and in situ 19 F magic-angle spinning nuclear magnetic resonance. Using the intermediate structure, we then calculate the monodomain polarization switching barrier in KNaNbOF 5 to be ~ 93 meV per formula unit, comparable to existing ferroelectrics. The reversal of the polarization is due to uncompensated antipolar displacements of oxygen and fluorine and does not require oxygen and fluorine site exchange as in other nonswitchable heteroanionic materials, which makes KNaNbOF 5 a viable oxyfluoride for a switchable electric polarization.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Si-based materials for lithium-ion batteries IV: Surface-modified Si/C/perfluorooctene powder

X-ray photoelectron spectroscopy was used to analyze nano-Si/C/perfluorooctene powder obtained from Paraclete Energy Inc. The spectra were obtained using incident monochromatic Al K α radiation at 1486.6 eV (0.834 01 nm). An initial survey spectrum together with F 1s, O 1s, C 1s, and Si 2p are presented. A final survey spectrum was collected to ascertain the amount of beam-induced damage, which appears to be minimal. Finally, the spectra indicate the principal core level photoelectron and Auger electron signals with only minor nitrogen signal and show the expected silicon-carbon, carbon-fluorine, and silicon-fluorine species related to the surface modification process in addition to oxidized carbon and silicon due to atmospheric exposure.

25 ENERGY STORAGE↗
DOE OSTI2020

Si-based materials for lithium-ion batteries XI. 70% surface-modified Si/C/perfluorooctene-carbon black/lithiated polyacrylic acid electrode

X-ray photoelectron spectroscopy was used to analyze a 70% Si/C/perfluorooctene-carbon black/lithiated polyacrylic acid electrode fabricated at the Cell Analysis, Modeling, and Prototyping (CAMP) Facility, Argonne National Laboratory. The spectra were obtained using incident monochromatic Al K α radiation at 1486.6 eV (0.83 401 nm). A survey spectrum together with O 1s, C 1s, and Si 2p are presented. The spectra indicate the principal core level photoelectron and Auger electron signals with only minor sodium, copper, calcium, and lithium signals and show the expected silicon-carbon, carbon-fluorine, and silicon-fluorine species related to the surface modification process in addition to oxidized carbon and silicon due to atmospheric exposure.

25 ENERGY STORAGE↗
DOE OSTI2023

Challenges in atomic layer etching of gallium nitride using surface oxidation and ligand-exchange

Two atomic layer etching (ALE) methods were studied for crystalline GaN, based on oxidation, fluorination, and ligand exchange. Etching was performed on unintentionally doped GaN grown by hydride vapor phase epitaxy. For the first step, the GaN surfaces were oxidized using either water vapor or remote O 2 -plasma exposure to produce a thin oxide layer. Removal of the surface oxide was addressed using alternating exposures of hydrogen fluoride (HF) and trimethylgallium (TMG) via fluorination and ligand exchange, respectively. Several HF and TMG super cycles were implemented to remove the surface oxide. Each ALE process was monitored in situ using multiwavelength ellipsometry. X-ray photoelectron spectroscopy was employed for the characterization of surface composition and impurity states. Additionally, the thermal and plasma-enhanced ALE methods were performed on patterned wafers and transmission electron microscopy (TEM) was used to measure the surface change. The x-ray photoelectron spectroscopy measurements indicated that F and O impurities remained on etched surfaces for both ALE processes. Ellipsometry indicated a slight reduction in thickness. TEM indicated a removal rate that was less than predicted. In conclusion, we suggest that the etch rates were reduced due to the ordered structure of the oxide formed on crystalline GaN surfaces.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Low-temperature etching of silicon oxide and silicon nitride with hydrogen fluoride

Etching of high aspect ratio features into alternating SiO 2 and SiN layers is an enabling technology for the manufacturing of 3D NAND flash memories. In this paper, we study a low-temperature or cryo plasma etch process, which utilizes HF gas together with other gas additives. Compared with a low-temperature process that uses separate fluorine and hydrogen gases, the etching rate of the SiO 2 /SiN stack doubles. Both materials etch faster with this so-called second generation cryo etch process. Pure HF plasma enhances the SiN etching rate, while SiO 2 requires an additional fluorine source such as PF 3 to etch meaningfully. Further, the insertion of H 2 O plasma steps into the second generation cryo etch process boosts the SiN etching rate by a factor of 2.4, while SiO 2 etches only 1.3 times faster. We observe a rate enhancing effect of H 2 O coadsorption in thermal etching experiments of SiN with HF. Ammonium fluorosilicate (AFS) plays a salient role in etching of SiN with HF with and without plasma. AFS appears weakened in the presence of H 2 O. Density functional theory calculations confirm the reduction of the bonding energy when NH 4 F in AFS is replaced by H 2 O.

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

High-voltage water-scarce hydrogel electrolytes enable mechanically safe stretchable Li-ion batteries

Soft Li-ion batteries, based on conventional organic electrolytes, face performance degradation challenges due to moisture penetration and safety concerns due to possible leakage of toxic fluorine compounds and flammable solvents under mechanical damage. We design a water-scarce hydrogel electrolyte with fluorine-free lithium salt to achieve wide electrochemical stability window (up to 3.11 volts) in ambient air without hermetic packaging while balancing high stretchability (1348%), ion conductivity (41 millisiemens per centimeter), and self-healing capabilities for mechanically and chemically safe stretchable Li-ion batteries. Molecular synergy between hydrophilicity and lithiophilicity of zwitterionic polymer backbone is revealed by molecular dynamics simulations. The battery exhibits capacity retention under harsh mechanical stresses—enduring stretching, twisting, folding, and multiple through-punctures by a needle—while self-healing from repeated through cuts by a razor blade. Stable ambient operation for 1 month over 500 charge-discharge cycles (average coulomb efficiency, 95%) is achieved. A prototype self-healing electronic system with embedded soft batteries demonstrates practical application as a durable embodied energy source.

Science & Technology - Other Topics↗
DOE OSTI2021

Editors’ Choice—Necessity to Avoid Titanium Oxide as Electrocatalyst Support in PEM Fuel Cells: A Membrane Durability Study

Pt/TiO 2 as electrocatalyst was found to significantly increase the rate of the membrane chemical degradation in a polymer electrolyte membrane (PEM) fuel cell. The increased degradation was proved to be due to TiO x (TiO 2 or Ti 4 O 7 ), which is widely recognized as a promising corrosion-resistant electrocatalyst support. The membrane degradation (thinning) appears to be preferentially in the side facing anode electrode. Migrated Ti species as a result of TiO x dissolution during fuel cell operation in an acidic environment was quantified by electron probe microanalysis (EPMA). Total fluorine inventory loss of the membrane strongly depends on the quantity of migrated Ti species (likely Ti 3+ and/or Ti 4+ ). The membrane chemical degradation induced by TiO x is proposed to be due to dissolved ionic Ti species reacting with H 2 O 2 through a Fenton reaction. TiO x is determined to be inviable as electrocatalyst support for PEM fuel cells, and future research is suggested to be directed toward alternative oxides with similar corrosion-resistance.

08 HYDROGEN↗
DOE OSTI2022

Evaluating the Effect of Electrolyte Additive Functionalities on NMC622/Si Cell Performance

Unstable electrode/electrolyte interface is the major cause of degradation for silicon (Si)-based anodes for lithium (Li)-ion batteries. Development of functional electrolyte additives can provide a viable path toward stabilizing the dynamic Si/electrolyte interface, which will benefit the development of high energy density Li-ion batteries. Here, we evaluate polymerizable electrolyte additives with varying functional groups (fluorocarbon, thiophosphate, and fluorophosphazene). The additives are examined using LiNi 0.6 Mn 0.2 Co 0.2 O 2 /Si full cells where the cycle performance and impedance are measured. Electrochemical tests show that the fluorine-containing additives provide better passivation at the Si electrode, leading to enhanced full cell performance. Here, among the three additives examined, best electrochemical performance is observed from the fluorocarbon-containing compound, followed by fluorophosphazene- and thiophosphate-containing compounds. Characterization of the solid electrolyte interphase (SEI) on cycled electrodes using Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) reveal that higher concentration of fluorine and lithium oxide, and lower concentration of carbonate and organic species correlate with enhanced electrochemical performance.

25 ENERGY STORAGE↗
DOE OSTI2026

Quantifying SEI Reaction Rate in the Presence and Absence of Mn 2+

In this work, a methodology utilizing potentiostatic holds is developed for measuring side-reaction rates at graphite (Gr) electrodes. The influence of Mn 2+ on parasitic reactions is evaluated in the presence of various preformed solid-electrolyte interphases (SEI). Gr SEI preformation was carried out using vinylene carbonate (VC) or lithium difluoro(oxalato)borate (LiDFOB) as an additive. In addition, a highly fluorinated electrolyte, free of traditional non-fluorinated organic carbonates, was used. Parasitic current increases were observed for all preformed Gr SEIs when Mn 2+ was present. Of the preforming electrolytes, the VC-derived SEI showed the lowest parasitic currents both with and without Mn 2+ .

Tornheim, Adam [Argonne National Laboratory (ANL),↗