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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Rational Design of Fluorinated Electrolytes for Low Temperature Lithium‐Ion Batteries

Abstract Nonaqueous carbonate electrolytes are commonly used in commercial lithium‐ion battery (LIB). However, the sluggish Li + diffusivity and high interfacial charge transfer resistance at low temperature (LT) limit their wide adoption among geographical areas with high latitudes and altitudes. Herein, a rational design of new electrolytes is demonstrated, which can significantly improve the low temperature performance below −20 °C. This electrolyte is achieved by tailoring the chemical structure, i.e., altering the fluorination position and the degree of fluorination, of ethyl acetate solvent. It is found that fluorination adjacent to the carbonyl group or high degree of fluorination leads to a stronger electron‐withdrawing effect, resulting in low atomic charge on the carbonyl oxygen solvating sites, and thus low binding energies with Li + ions at LT. The optimal electrolyte 2,2,2‐trifluoroethyl acetate (EA‐f) shows significantly improved cycle life and C‐rate of a NMC622/graphite cell when cycled at −20 °C and −40 °C, respectively. In addition to superior LT performance, the electrolyte is nonflammable and tolerant for high voltage charging all owing to its fluorine content. This work provides guidance in designing next‐generation electrolytes to address the critical challenge at subzero temperatures.

25 ENERGY STORAGE↗
DOE OSTI2021

Benchmark CO 2 separation achieved by highly fluorinated nanoporous molecular sieve membranes from nonporous precursor via in situ cross-linking

Molecular sieve membranes with rigid micropores and CO 2 -philic functionalities within the architectures are promising candidates in CO 2 separation. However, the development of ctieve approaches for their fabrication still remains a significant challenge. In this study, an in situ cross-linking strategy is developed for the preparation of nanoporous fluorinated moleffecular sieve membranes using commercially available dense and non-porous polystyrene (M PS ) as a precursor template. Based on the dehydrative Friedel-Crafts reactions with highly fluorinated benzylic alcohols, M PS membranes are cross-linked in situ upon exposure to Brønsted acid (CF 3 SO 3 H), affording fluorinated microporous polymeric membranes with surface areas up to 523 m 2 g –1 and the presence of micropores centered at 1.1–1.3 nm as well as ultra-micropores (~0.6 nm). The obtained modified membranes exhibit good ideal CO 2 permeability of 797 barrer and CO 2 /N 2 selectivity of 28.5. In addition, high fluorine content (up to 28.5 wt%) and good thermal stability made the cross-linked membranes promising candidates to produce fluorinated carbon molecular sieve membranes with improved textural properties, exhibiting surface areas up to 1020 m 2 g –1 and ultra-micropores of ~0.4 nm. These membranes achieve superior CO 2 /N 2 separation performances exceeding the Robeson upper bound limit (2008).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Direct Mapping of Fluorine in Cation Disordered Rocksalt Cathodes

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

(S)TEM↗
DOE OSTI2025

Alternative Solid‐State Synthesis Route for Highly Fluorinated Disordered Rock‐Salt Cathode Materials for High‐Energy Lithium‐Ion Batteries

Abstract Fluorination has been identified as a key element for enabling the stable cycling of earth‐abundant manganese‐based disordered rock salt (DRX) cathodes. However, fluorination in the DRX bulk remains a challenge for scalable solid‐state synthesis. In this study, a tailored reaction pathway is proposed to synthesize a highly fluorinated DRX. It is demonstrated for the first time that the unconventional precursors, Li 6 MnO 4 , MnF 2 , and TiO 2 , can avoid the formation of Mn‐based intermediates (such as Li 2 (Mn,Ti)O 3, LiMnO 2 , and Mn 3 O 4 ), which, once formed, persist until the synthesis temperature reaches close to or above that required for fluorine volatility. Therefore, this method can form a highly fluorinated DRX with a composition of Li 1.23 Mn 0.40 Ti 0.37 O 2−y F y ( y = 0.29–0.34) at a low temperature (800 °C) relative to that required for conventional DRX solid‐state reactions (≥900 °C). Li 1.23 Mn 0.40 Ti 0.37 O 2−y F y ( y = 0.29–0.34) delivers a specific capacity above 300 mAh g −1 and a specific energy of 980 Wh kg −1 at 30 °C. Detailed characterization reveals that this DRX phase reversibly utilizes Mn 2+/3+ redox in the low‐voltage region and Mn 3+/4+ redox in the middle‐voltage range, whereas reversible oxygen redox is observed at high potentials.

Avvaru, Venkata Sai↗
DOE OSTI2022

Understanding the Fluorination of Disordered Rocksalt Cathodes through Rational Exploration of Synthesis Pathways

Here, we have designed and tested several synthesis routes targeting a highly fluorinated disordered rocksalt (DRX) cathode, Li 1.2 Mn 0.4 Ti 0.4 O 1.6 F 0.4 , with each route rationalized by thermochemical analysis. Precursor combinations were screened to raise the F chemical potential and avoid the formation of LiF, which inhibits fluorination of the targeted DRX phase. MnF 2 was used as a reactive source of F, and Li 6 MnO 4 , LiMnO 2 , and Li 2 Mn 0.33 Ti 0.66 O 3 were tested as alternative Li sources. Each synthesis procedure was monitored using a multi-modal suite of characterization techniques including X-ray diffraction, nuclear magnetic resonance, thermogravimetric analysis, and differential scanning calorimetry. From the resulting data, we advance the understanding of oxyfluoride synthesis by outlining the key factors limiting F solubility. At low temperatures, MnF 2 consistently reacts with the Li source to form LiF as an intermediate phase, thereby trapping F in strong Li-F bonds. LiF can react with Li 2 TiO 3 to form a highly lithiated and fluorinated DRX (Li 3 TiO 3 F); however, MnO is not easily incorporated into this DRX phase. Although higher temperatures typically increase solubility, the volatility of LiF above its melting point (848 °C) inhibits fluorination of the DRX phase. Based on these findings, metastable synthesis techniques are suggested for future work on DRX fluorination.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Synthesizing High-Capacity Oxyfluoride Conversion Anodes by Direct Fluorination of Molybdenum Dioxide (MoO 2 )

High-capacity metal oxide conversion anodes for lithium-ion batteries (LIBs) are primarily limited by their poor reversibility and cycling stability. In this study, a promising approach has been developed to improve the electrochemical performance of a MoO 2 anode by direct fluorination of the prelithiated MoO 2 . The fluorinated anode contains a mixture of crystalline MoO 2 and amorphous molybdenum oxyfluoride phases, as determined from a suite of characterization methods including X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy, and scanning transmission electron microscopy. Electrochemical measurements indicate that fluorination facilitates the conversion reaction kinetics, which leads to increased capacity, higher coulombic efficiency, and better cycling stability as compared to the nonfluorinated samples. Overall, these results suggest that fluorination after prelithiation not only favors formation of the oxyfluoride phase but also improves the lithium-ion diffusivity and reversibility of the conversion reaction, making it an attractive approach to address the problems of conversion electrodes. These findings provide a new route to design high-capacity negative electrodes for LIBs.

25 ENERGY STORAGE↗
DOE OSTI2025

Extending the operating range and safety of Li-ion batteries with new fluorinated electrolytes

Orbia Fluor and Energy Materials (formerly Koura) has successfully developed a new class of fluorinated electrolyte solvents for lithium-ion batteries. In collaboration with Silatronix and Argonne National Laboratory, the team synthesized and screened over 20 novel fluorinated compounds, optimizing formulations that significantly enhance battery performance across critical metrics such as thermal stability, fast-charging capability, and cycling life at extreme temperatures. Electrolytes with fluorinated molecules developed in this program demonstrated superior performance in 2 Ah pouch cells, achieving over 1000 fast-charge cycles with minimal capacity fade, outperforming conventional carbonate-based electrolytes. Mechanistic studies revealed that the fluorinated electrolytes promote a stable solid electrolyte interphase at the anode and reduce cathode metal dissolution, contributing to improved long-term stability. These advancements mark a significant step toward safer, more efficient batteries for applications ranging from grid storage to defense systems to electric vehicles. We gratefully acknowledge DOE’s financial support through contract DE-EE0009642.

25 ENERGY STORAGE↗
DOE OSTI2026

Stereochemically‐Controlled Fluorinated Copolymers for Selectively Permeable Barrier Applications

Selective oxygen permeability coupled with low water vapor transmission is essential for biomedical and packaging applications requiring controlled oxygen flux under humid conditions. However, most high‐performance barrier polymers depend on perfluoroalkyl substances (PFAS), whose persistence and regulatory restrictions limit their long‐term applicability. We designed a series of stereocontrolled thiol‐yne‐based polyesters, including both fluorinated and non‐fluorinated variants, for selective oxygen permeability with considerable water barrier performance. Tailoring polymer crystallinity and morphology tuned both oxygen transport and mechanical properties. Fluorinated polymers demonstrated enhanced hydrophobicity and water resistance while maintaining oxygen diffusivity within a range relevant to oxygen‐sensing applications. Structure–property relationships were elucidated through small‐ and wide‐angle X‐ray scattering, revealing semi‐crystalline domains influenced by fluorine content and dithiol chain length. Barrier performance was rigorously evaluated via water vapor transmission rate and dynamic vapor sorption, showing reduced water uptake with increasing dithiol monomer length and crystallinity. In conclusion, this work introduces a PFAS‐free alternative to conventional barrier materials and establishes a tunable materials platform with potential relevance for biomedical devices and packaging systems requiring controlled oxygen permeability.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Tuning the surface energy of fluorinated diamond-like carbon coatings via plasma immersion ion implantation plasma-enhanced chemical vapor deposition with 1,1,1,2-tetrafluoroethane

Here, we demonstrate an environmentally friendly and scalable method to create fluorine-doped diamond-like carbon (F-DLC) coatings using plasma immersion ion implantation plasma-enhanced chemical vapor deposition (PIII-PECVD) with 1,1,1,2-tetrafluoroethane. F-DLC films tend to have low wettability and good mechanical flexibility, which make them suitable for applications in biomedical devices and antibiofouling surfaces. We report on the effects of fluorine incorporation on the surface chemistry, surface energy, and morphology of these coatings, showing that our method is effective in increasing the fluorine content in the F-DLC up to 40%. We show that the addition of fluorine leads to a decrease in surface energy, which is consistent with a reduction in surface wettability.

Contact angle↗
DOE OSTI2023

Tuning Bulk Redox and Altering Interfacial Reactivity in Highly Fluorinated Cation-Disordered Rocksalt Cathodes

Lithium-excess, cation-disordered rocksalt (DRX) materials have been subject to intense scrutiny and development in recent years as potential cathode materials for Li-ion batteries. Despite their compositional flexibility and high initial capacity, they suffer from poorly understood parasitic degradation reactions at the cathode-electrolyte interface. These interfacial degradation reactions deteriorate both the DRX material and electrolyte, ultimately leading to capacity fade and voltage hysteresis during cycling. In this work, differential electrochemical mass spectrometry (DEMS) and titration mass spectrometry are combined to quantify the extent of bulk redox and surface degradation reactions for a set of Mn 2+/4+ -based DRX oxyfluorides during initial cycling with a high-voltage charging cutoff (4.8 V vs Li/Li + ). Increasing the fluorine content from 7.5 to 33.75% is shown to diminish oxygen redox and suppresses high-voltage O 2 evolution from the DRX surface. Additionally, electrolyte degradation processes resulting in the formation of both gaseous species and electrolyte-soluble protic species are observed. Subsequently, DEMS is paired with a fluoride-scavenging additive to demonstrate that increasing fluorine content leads to increased dissolution of fluorine from the DRX material into the electrolyte. Finally, a suite of ex situ spectroscopy techniques (X-ray photoelectron spectroscopy, inductively coupled plasma optical emission spectroscopy, and solid-state nuclear magnetic resonance spectroscopy) are employed to study the change in DRX composition during charging, revealing the dissolution of manganese and fluorine from the DRX material at high voltages. Here this work provides insight into the degradation processes occurring at the DRX-electrolyte interface and points toward potential routes of interfacial stabilization.

25 ENERGY STORAGE↗
DOE OSTI2024

Methylation enables the use of fluorine-free ether electrolytes in high-voltage lithium metal batteries

Lithium metal batteries represent a promising technology for next-generation energy storage, but they still suffer from poor cycle life due to lithium dendrite formation and cathode cracking. Fluorinated solvents can improve battery longevity by improving LiF content in the solid-electrolyte interphase; however, the high cost and environmental concerns of fluorinated solvents limit battery viability. Here, for this work, we designed a series of fluorine-free solvents through the methylation of 1,2-dimethoxyethane, which promotes inorganic LiF-rich interphase formation through anion reduction and achieves high oxidation stability. The anion-derived LiF interphases suppress lithium dendrite growth on the lithium anode and minimize cathode cracking under high-voltage operation. The Li + -solvent structure is investigated through in situ techniques and simulations to draw correlations between the interphase compositions and electrochemical performances. The methylation strategy provides an alternative pathway for electrolyte engineering towards high-voltage electrolytes while reducing dependence on expensive fluorinated solvents.

25 ENERGY STORAGE↗
DOE OSTI2024

Deposition temperature-mediated growth of helically shaped polymers and chevron-type graphene nanoribbons from a fluorinated precursor

Graphene nanoribbons (GNRs) of precise size and shape, critical for controlling electronic properties and future device applications, can be realized via precision synthesis on surfaces using rationally designed molecular precursors. Fluorine-bearing precursors have the potential to form GNRs on nonmetallic substrates suitable for device fabrication. Here, we investigate the deposition temperature-mediated growth of a new fluorine-bearing precursor, 6,11-diiodo-1,4-bis(2-fluorophenyl)-2,3-diphenyltriphenylene (C 42 H 24 F 2 I 2 ), into helically shaped polymer intermediates and chevron-type GNRs on Au(111) by combining scanning tunneling microscopy, X-ray photoelectron spectroscopy, and density functional theory simulations. The fluorinated precursors do not adsorb on the Au(111) surface at lower temperatures, necessitating an optimum substrate temperature to achieve maximum polymer and GNR lengths. We compare the adsorption behavior with that of pristine chevron precursors and discuss the effects of C-H and C-F bonds. The results elucidate the growth mechanism of GNRs with fluorine-bearing precursors and establish a foundation for future synthesis of GNRs on nonmetallic substrates.

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

Revealing EDL-driven reduction mechanisms in binary, ternary, and quaternary fluorinated electrolytes via an integrated MD–DFT–ML framework

Accurately predicting solid electrolyte interphase (SEI) formation requires explicitly resolving the electric double layer (EDL) structure, which deviates significantly from that of the bulk electrolyte. Although an established molecular dynamics (MD) and Density Functional Theory (DFT) framework can model SEI formation by evaluating reduction reactions of local clusters in the EDL, it suffers from a combinatorial computational bottleneck. To overcome this limitation, we introduce a machine-learning-accelerated simulation workflow (MD–DFT–ML), integrating a gradient-boosted regression model trained on EDL composition data to efficiently predict reduction potentials. We apply this framework to seven fluorinated electrolytes comprising fluorinated anions, a fluorinated ester solvent, two types of diluent (ion-solvating ester vs. non-solvating ether), and an FEC additive. The analysis shows that the EDL selectively accumulates cation-binding species; consequently, the non–cation-binding ether diluent rarely enters the EDL and makes minimal contributions to SEI formation. DFT calculations on statistically representative EDL clusters provide reduction potentials and fluorine-release pathways, while the ML model, which substantially reduces the DFT workload, predicts cluster reduction energies with a mean absolute error of 0.1 eV. The combined MD–DFT–ML approach also quantifies contributions from different sources to LiF formation in the SEI. This methodology establishes a generalizable route for multiscale modeling electrolyte and interphase design for next-generation electrochemical energy-storage systems.

DFT-MD-ML workflow↗
DOE OSTI2023

Fluorine spillover for ceria- vs silica-supported palladium nanoparticles: A MD study using machine learning potentials

Supported metallic nanoparticles play a central role in catalysis. However, predictive modeling is particularly challenging due to the structural and dynamic complexity of the nanoparticle and its interface with the support, given that the sizes of interest are often well beyond those accessible via traditional ab initio methods. With recent advances in machine learning, it is now feasible to perform MD simulations with potentials retaining near-density-functional theory (DFT) accuracy, which can elucidate the growth and relaxation of supported metal nanoparticles, as well as reactions on those catalysts, at temperatures and time scales approaching those relevant to experiments. Furthermore, the surfaces of the support materials can also be modeled realistically through simulated annealing to include effects such as defects and amorphous structures. We study the adsorption of fluorine atoms on ceria and silica supported palladium nanoparticles using machine learning potential trained by DFT data using the DeePMD framework. We show defects on ceria and Pd/ceria interfaces are crucial for the initial adsorption of fluorine, while the interplay between Pd and ceria and the reverse oxygen migration from ceria to Pd control spillover of fluorine from Pd to ceria at later stages. In contrast, silica supports do not induce fluorine spillover from Pd particles.

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

Progress Towards Extended Cycle Life Si-based Anodes: Investigation of Fluorinated Local High Concentration Electrolytes

Silicon (Si) anodes are promising candidates for Li-ion batteries due to their high specific capacity and low operating potential. Implementation has been challenged by the significant Si volume changes during (de)lithiation and associated growth/regrowth of the solid electrolyte interphase (SEI). In this report, fluorinated local high concentration electrolytes (FLHCEs) were designed such that each component of the electrolyte (solvent, salt, diluent) is fluorinated to modify the chemistry and stabilize the SEI of high (30%) silicon content anodes. FLHCEs were formulated to probe the electrolyte salt concentration and ratio of the fluorinated carbonate solvents to a hydrofluoroether diluent. Higher salt concentrations led to higher viscosities, conductivities, and contact angles on polyethylene separators. Electrochemical cycling of Si-graphite/NMC622 pouch cells using the FLHCEs delivered up to 67% capacity retention after 100 cycles at a C/3 rate. Post-cycling X-ray photoelectron spectroscopy (XPS) analyses of the Si-graphite anodes indicated the FLHCEs formed a LiF rich solid electrolyte interphase (SEI). The findings show that the fluorinated local high concentration electrolytes contribute to stabilizing the Si-graphite electrode over extended cycling.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Fully Fluorinated Local High Concentration Electrolytes Enabling High Energy Density Si Anodes

To develop fluorinated localized high concentration electrolytes as a novel approach for constructing a functional SEI on Si based anodes. The technological approach combines the SEI modification strategies of fluorinated carbonate solvents and local high concentration electrolytes. The resulting synergy of anion and fluorinated solvent decomposition will form a mechanically robust, fluorinated SEI that enables extended cycling with high capacity retention. The electrolytes will enable demonstration of silicon-graphite anodes with high Si content, paired with NMC811 cathodes. Characterization will focus on galvanostatic cycling to evaluate electrochemical performance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Toward Stable Cycling of a Cost-Effective Cation-Disordered Rocksalt Cathode via Fluorination

The recently developed Li-excess cation-disordered rock salts (DRXs) exhibit an excellent chemical diversity for the development of alternative Co/Ni-free high-energy cathodes. Herein, the synthesis of a highly fluorinated DRX cathode, Li 1.2 Mn 0.6 Ti 0.2 O 1.8 F 0.2 , based on cost-effective and earth-abundant transition metals, via a solid-state reaction, is reported. The fluorinated DRX cathode using ammonium fluoride precursor exhibits more uniform particle size and delivers a specific discharge capacity of 233 mAh g -1 and specific energy of 754 Wh kg -1 , with 206 mAh g -1 retained after 200 cycles. Further, the combined synchrotron X-ray absorption spectroscopy and resonant inelastic X-ray scattering spectroscopy analysis reveals that the remarkable cycling performance is attributed to the high fluorination and thus enhanced Mn content, enabling the utilization of more Mn redox than the oxide analog. This study demonstrates a great promise to develop next-generation cost-effective DRX cathodes with enhanced capacity retention for high-energy Li-ion batteries.

25 ENERGY STORAGE↗
DOE OSTI2023

Developing Efficient Benzene Additives for 19.43% Efficiency of Organic Solar Cells by Crossbreeding Effect of Fluorination and Bromination

Employing volatile solid additives have emerged as a promising method to optimize the morphology and improve the performance of organic solar cells (OSCs). However, principles governing the efficient design of solid additives remain elusive. In this work, the programmed fluorination and/or bromination on benzene core to develop efficient additives for OSCs is reported. The programmed fluorination and/or bromination endow the five halogen benzene derivatives, 1,3,5-trifluorobenzene, hexafluorobenzene, 1,3,5-tribromo-2,4,6-trifluorobenzene (TFTB), 1,3,5-tribromobenzene, and hexabromobenzene, with different melting and boiling points, volatility, as well as interactions with the host blend. Studies indicate that the additives with extremely high and low volatility are almost powerless and even detrimental to the morphology evolution. Among them, the combination of fluorine and bromine atoms on TFTB not only enables the more appropriate m.p./b.p. and volatility, but also exerts stronger molecular interactions with the host blend, giving rise to higher ordered molecular packing and more favorable morphology. Importantly, TFTB exhibits good universality to optimize the performances of OSCs with high power conversion efficiencies (PCEs; over 18%) in a group of binary blend systems, and an impressive PCE of 19.43% in the ternary PBTz-F:PM6:L8-BO system.

36 MATERIALS SCIENCE↗