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At least 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

The Impact of Different Substituents in Fluorinated Cyclic Carbonates in the Performance of High Voltage Lithium-Ion Battery Electrolyte

Ethylene carbonate (EC) has been used as the Solid-Electrolyte Interphase (SEI) former in the conventional electrolyte for decades. However, its low anodic stability leads to severe capacity decay during cycling under high voltage operation. Therefore, finding a viable electrolyte with high anodic stability and the ability to form robust SEI for high voltage lithium-ion batteries is of primary importance. In this study, a series of electrolytes containing various fluorinated cyclic carbonates as the SEI former have been designed, synthesized and evaluated. Linear sweep voltammetry study suggested that fluorinated cyclic carbonates generally possess higher anodic stability than EC. Based on the cycling performance of LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NMC532)/ graphite full cells, the electrolyte with DFEC/FEMC (1.0 M LiPF 6 ) inhibited the oxidation side reaction on the cathode and forms a vigorous SEI on the anode. The high voltage NMC532/Graphite cell utilizing the novel electrolyte exhibits excellent cycling durability under both room and elevated temperature. The superior performance of the DFEC based electrolyte was further unveiled by SEM, EDAX and XRD. Both the anode and cathode of the full cell employing DFEC based electrolyte retained their intrinsic structures after cycling while the electrodes cycled in conventional electrolyte showed severe degradation.

25 ENERGY STORAGE↗
DOE OSTI2023

Assessing Electrolyte Fluorination Impact on Calendar Aging of Blended Silicon-Graphite Lithium-Ion Cells Using Potentiostatic Holds

Silicon-based lithium-ion batteries have started to meet cycle life metrics, but they exhibit poor calendar life. Here, electrolyte fluorination impact on calendar fade of blended silicon-graphite anodes is explored using a LiPF 6 in EC:EMC:FEC electrolyte vs LiBOB in EC:EMC electrolyte. We utilize a combined experimental-modeling approach applying potentiostatic voltage holds (V-hold) to evaluate electrolyte suitability for calendar life in a shortened testing timeframe (~2 months). Our theoretical framework deconvolutes the irreversible parasitic capacity losses (lithium lost to the solid electrolyte interphase) from the V-hold electrochemical data. Unfluorinated electrolyte (dominant LiBOB reduction) exhibits higher cell resistance as compared to fluorinated electrolyte (dominant FEC reduction). Both systems have similar irreversible capacities during the voltage hold duration with slower rate of parasitic capacity loss for the LiBOB system. Extrapolation of the parasitic losses to end of life capacity fade of 20% shows LiBOB electrolyte outperforming LiPF 6 electrolyte in calendar life. The results demonstrate the applicability of the V-hold protocol as a rapid material screening tool providing semi-quantitative calendar lifetime estimates.

25 ENERGY STORAGE↗
DOE OSTI2023

Unveiling the transport properties of protic ionic liquids: Lithium ion dynamics modulated by the anion fluorine reservoir

Protic ionic liquids (PILs) show great potential as electrolyte components for energy storage devices. A comprehensive understanding of their transport properties must be achieved to optimize the design of safer and efficient electrolytes. This study focuses on a series of PILs based on the DBUH + cation (protonated 1,8-diazabicyclo[5,4,0]–undec-7-ene superbase) and three anions derived from strong acids: TFO – (triflate), IM14 – (perfluorobutyl-trifluoromethylsulfonylimide) and TFSI – (bis(trifluoromethylsulfonyl)imide). Neat PILs and PILs doped with LiTFO, LiIM14, and LiTFSI were studied using temperature-dependent NMR diffusion and relaxation techniques. The ionicity of these systems was also evaluated. Results revealed that the dynamic behaviour of lithium ions, as well as ionicity, strongly depend on the structural features of the anions, particularly in the case of IM14 – , whose main feature is the uneven distribution of the fluorinated sidegroups. The 19 F relaxation rates in IM14 – provide insights into the rotational reorientation of that anion. DBUH-IM14 exhibited diffusion coefficients lower than the expected ones on the basis of its viscosity, likely due to fluorophilic intermolecular interactions involving the fluorinated terminal groups. The presence of Li + in the DBUH-IM14 electrolyte led to unexpected and relatively faster translational mobility of Li + ions, resulting in a higher lithium apparent transference number. However, the trends observed in ionicity indicate a more complex interplay between intermolecular interactions and ion correlations. While DBUH-TFSI showed minimal effect of Li + addition, DBUH-TFO and DBUH-IM14 exhibited a significant decrease in ionicity, possibly attributed to strong interactions between ions.

25 ENERGY STORAGE↗
DOE OSTI2025

Fluorinated polythiophenes with ester side chains for boosting the V OC and efficiency in non-fullerene polymer solar cells

As the power conversion efficiency (PCE) of organic photovoltaics (OPVs) approximates the 19 % threshold, wide bandgap (WBG) polythiophenes (PTs) have gained increasing attention due to their simple chemical structures and ease of synthesis, making them promising candidates for large-scale production. However, the benchmark polymer poly(3-hexylthiophene) (P3HT) is limited by its high-lying HOMO energy level, which restricts the open-circuit voltage (V OC ) in solar cells. Here, in this study, we introduce a novel series of PT derivatives (PDC8-T, PDC8-3T, PDC16-3T, and PDC16-3T-2F) featuring ester side chains designed to fine-tune electronic properties through a streamlined three-step synthesis. Additionally, we incorporated a π-spacer to reduce steric hindrance and elongated alkyl side chains to improve solubility and processability. Compared to P3HT, these PT derivatives demonstrate a significant reduction in HOMO energy levels, lowering by approximately 0.3–0.4 eV. Among them, PDC16-3T-2F—with fluorine atom substitution—achieves the lowest HOMO energy level, induces a coplanar molecular conformation, and enhances polymer aggregation behavior. We evaluated these PT derivatives in inverted non-fullerene bulk-heterojunction (NFA BHJ) OPVs. The PDC8-3T device showed a relatively low PCE of 0.69 %, with a V OC of 0.76 V, a short-circuit current density (J SC ) of 3.32 mA/cm 2 , and a fill factor (FF) of 27.3 %. In contrast, the PDC16-3T-2F device achieved an impressive PCE of 7.21 %, with a V OC of 0.85 V, a J SC of 14.60 mA/cm 2 , and an FF of 58.4 %. This remarkable improvement is attributed to the fluorine substitution, which not only enhances molecular orientation but also downshifts the HOMO energy level and further boosts the V OC . Hence, these molecular design strategies have led to a fibrillar bicontinuous interpenetrating network with optimal nanoscale phase separation within the active layer.

14 SOLAR ENERGY↗
DOE OSTI2026

Lithium–Sulfur Batteries Enabled by Fluorine-Free Electrolytes with a Compressed Solvation Structure

In this paper, a fluorine-free aromatic cosolvent strategy is presented to regulate electrolyte solvation chemistry in Li-S batteries with sulfurized polyacrylonitrile (SPAN) cathodes. Assisted by the Uni-ELF AI tool and experimental validation, toluene is identified as an optimal weakly solvating cosolvent. Its incorporation compresses the Li⁺ solvation sheath and induces an anion-dominated solvation structure, thereby enhancing interfacial ion transport and sulfur redox kinetics through controlled π-π interactions with polysulfides. Consequently, Li || Li symmetric cells exhibit stable cycling for over 1,000 cycles at a current density of 1 mA cm⁻². Meanwhile, Li-S cells employing high-loading SPAN cathodes retain more than 75% of their initial capacity after 250 cycles at -10 °C. Additionally, a practical pouch cell with high SPAN loading and a low electrolyte-to-SPAN ratio of 3 µL mg⁻¹ delivers an initial capacity of around 600 mAh gSPAN⁻¹, underscoring the potential of fluorine-free electrolytes for practical metal-sulfur batteries.

25 ENERGY STORAGE↗
DOE OSTI2020

Comparative analysis of characteristics of a supersonic cw chemical HF laser on molecular fluorine and nitrogen trifluoride

We have experimentally studied the characteristics of a supersonic cw chemical HF laser with a flat nozzle array based on a nozzle – nozzle reagent mixing scheme operating with the use of F{sub 2} – D{sub 2} – He and NF{sub 3} – D{sub 2} – He fuel compositions in an atomic fluorine generator. The active medium flow field pattern, its gas-dynamic characteristics, and the laser radiation spectrum are considered. The comparison of these characteristics has made it possible to establish a strong impact on the flow field (lasing zone length) of the chemical composition of the combustion products from the atomic fluorine generator. The gas-dynamic parameters of the active medium formed by using a NF{sub 3} – D{sub 2} – He fuel have turned out to be less acceptable in terms of the gas flow pressure recovery than in the case of F{sub 2} – D{sub 2} – He fuel, while the radiation spectrum was more preferable from the viewpoint of passing through the atmosphere. (paper)

36 MATERIALS SCIENCE↗
DOE OSTI2020

Efficient lasing in mixtures of helium and fluorine in diffuse discharges formed by runaway electrons

The parameters of stimulated lasing in diffuse discharges formed in mixtures of helium and fluorine in a strongly inhomogeneous electric field are investigated. Lasing is obtained in the visible and VUV spectral regions on the transitions of fluorine atoms and molecules. It is shown that lasing in He – F{sub 2} mixtures at a wavelength of 157 nm continues for several half-periods of the discharge current. Due to the homogeneity of the diffuse discharge, the maximum lasing efficiency of the F{sub 2} laser is 0.15 %, which corresponds to the efficiency of this type of lasers pumped by pre-ionised transverse volume discharges. (paper)

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

Fluorine Limits and Impacts in High-Level Waste Glass Compositions

The impact of elevated fluorine (F) content on Hanford high-level waste (HLW) glasses has not previously been studied in detail. This effort represents the first systematic study to determine what F concentration limits should be used for the design of alkali-borosilicate-based Hanford Waste Treatment and Immobilization Plant (WTP) HLW glasses, and to document the technical basis for that limit. If alkali borosilicate glass made from Hanford HLW can accommodate a large amount of F, the large capital costs for complex sludge washing facilities may be avoided, as would much of the operational costs and negative schedule impacts associated with handling the large volumes of water required to dissolve these salts. In order to determine a limit for F in likely HLW glass compositions, an evaluation was conducted on glasses with F ≤ 0.90 mass% from previous nuclear waste glass studies. The collected dataset contains 239 glasses (232 HLW glasses and 7 LAW glasses) including 109 glasses with 0.9 ≤ F mass% ≤ 2.5, 116 with 2.5 < F mass% ≤ 8.0, and 14 with F mass% ≥ 8 (max. F mass% = 17.42). The collected composition and property data were analyzed to determine the basis for the F tolerance, i.e. the maximum F concentration that can be processed without potential issues. Fluorine volatility, product consistency test (PCT) response, liquidus temperature (T L ), glass melt viscosity, and crystallinity have been investigated. No limits for F concentration can be made based on F volatility, T L , or glass melt viscosity, because the data show that high F in glasses do not indicate, with high probability, being restricted by those property constrains. However, crystallinity and PCT response were used to estimate the F tolerance. The results show that glasses with high F (≥ 0.90 mass%) are more likely to form large fractions of F-containing crystal phases which may increase PCT responses, i.e. decrease the glass durability. Based on the results of crystallinity and PCT data, the F tolerance of 4.5 mass% is estimated. There is no evidence of other glass components, such as calcium oxides and alkali metal oxides have combined impacts with F on the glass properties. Overall, the available high-F glass data is limited, especially in the designed HLW glass composition regions. Future work on formulation and testing of HLW glasses with F ≥ 0.9 mass% will close the data gaps and expand operational flexibility with respect to the fluoride tolerances. Volatility of F from melters and corrosion of materials in contact with glass melts are important for processing of high-F wastes; yet no test data are currently available. It is recommended tests be conducted to address these two potential issues.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
NASA NTRS1994

Fluorine Implantation and Residual Stresses in Polysilicon Films

As microelectronic device dimensions are reduced below one micron, the hot carrier effect is a major barrier to continued scaling and VLSI reliability. Several reports have shown that fluorine diffusion into the device gate greatly enhances the resistance to hot carriers. There has been some disagreement as to the mechanism of influence; however, several reports have suggested that the polysilicon is physically modified by the fluorine implant and that the beneficial effects are at least in part due to stress relaxation in the polysilicon.

polysilicon fluorine microelectronic devices hot c↗
NASA NTRS2015

NIGMS Fluorine Detection

Please note that these charts were not presented at the CCMPP July 2015 Workshop; however, we would like to include these charts in the Workshop Proceedings.These charts present an overview of the NGIMS fluorine evaluation conducted for the MAVEN mission. The charts show that fluorine may be generated by the following mechanisms:-Reaction with water-Elevated temperature-Radiation, atomic oxygen, ultraviolet, spacecraft charging, and vacuum-Space environmental synergy

spacecraft contamination↗
DOE OSTI2022

Fluorination‐Enhanced Surface Stability of Disordered Rocksalt Cathodes

Abstract Cation‐disordered rocksalt (DRX) oxides are a promising new class of high‐energy‐density cathode materials for next‐generation Li‐ion batteries. However, their capacity fade presents a major challenge. Partial fluorine (F) substitution into the oxygen (O) lattice appears to be an effective strategy for improving the cycling stability, but the underlying atomistic mechanism remains elusive. Here, using a combination of advanced transmission electron microscopy based imaging and spectroscopy techniques, the structural and chemical evolution upon cycling of Mn‐based DRX cathodes with an increasing F content (Li–Mn–Nb–O–F x , x = 0, 0.05, 0.2) are probed. The atomic origin behind the beneficial effect of high‐level fluorination for enhancing the surface stability of the DRX is revealed. It is discovered that, due to the reduced O redox activity while with increasing F concentration, F in the DRX lattice mitigates the formation of an O‐deficient surface layer upon cycling. For low F‐substituted DRX, the O loss near the surface results in the formation of an amorphous cathode–electrolyte interphase layer and nanoscale voids after extended cycling. Increased F concentration in the DRX lattice minimizes both O loss and the interfacial reactions between DRX and the liquid electrolyte, enhancing the surface stability of DRX. These results provide guidance on the development of next‐generation cathode materials through anion substitution.

Li, Linze↗
DOE OSTI2024

Comprehensive review of combustion ion chromatography for the analysis of total, adsorbable, and extractable organic fluorine

Poly‐ and perfluoroalkyl substances (PFAS) are a class of persistent organic pollutants whose high stability and appreciable water solubility have led to near‐global contamination. PFAS are bioaccumulative toxins that have been linked to a myriad of disorders and have been detected nearly universally in human blood. Liquid chromatography‐tandem mass spectrometry is the most frequent method used for quantitation, though this typically only measures a few dozen of the >14 000 known PFAS and has been shown to account for a small portion of the total organic fluorine present. Sum parameter methods such as total, extractable, and adsorbable organic fluorine have emerged as alternative measurements for PFAS determination. Combustion ion chromatography has become the preferred method for organofluorine measurement where the sorbent or extract containing PFAS is combusted and the emitted hydrofluoric acid (HF) is a measure of the cumulative organofluorine present. Herein we critically review the types of organofluorine measurement, their separation from the sample matrix, and key parameters of the analytical instrument that affect sensitivity, reproducibility, and recovery with regards to PFAS analysis.

Chemistry↗
DOE OSTI2024

Ionic Pairs-Engineered Fluorinated Covalent Organic Frameworks Toward Direct Air Capture of CO 2

The covalent organic frameworks (COFs) possessing high crystallinity and capability to capture low-concentration CO 2 (400 ppm) from air are still underdeveloped. The challenge lies in simultaneously incorporating high-density active sites for CO 2 insertion and maintaining the ordered structure. Herein, a structure engineering approach is developed to afford an ionic pair-functionalized crystalline and stable fluorinated COF (F-COF) skeleton. The ordered structure of the F-COF is well maintained after the integration of abundant basic fluorinated alcoholate anions, as revealed by synchrotron X-ray scattering experiments. The breakthrough test demonstrates its attractive performance in capturing (400 ppm) CO 2 from gas mixtures via O$-$C bond formation, as indicated by the in situ spectroscopy and operando nuclear magnetic resonance spectroscopy using 13 C-labeled CO 2 sources. Both theoretical and experimental thermodynamic studies reveal the reaction enthalpy of ≈-40 kJ mol -1 between CO 2 and the COF scaffolds. This implies weaker interaction strength compared with state-of-the-art amine-derived sorbents, thus allowing complete CO 2 release with less energy input. The structure evolution study from synchrotron X-ray scattering and small-angle neutron scattering confirms the well-maintained crystalline patterns after CO 2 insertion. In conclusion, the as-developed proof-of-concept approach provides guidance on anchoring binding sites for direct air capture (DAC) of CO 2 in crystalline scaffolds.

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

Optimized molecular aggregation via incorporating fluorinated unit in the polymer donor for 17.3% efficiency organic solar cells

Regulating molecular aggregation state via chemical modification of photovoltaic materials to optimize the blend morphology is an effective and challenging strategy to improve the photovoltaic performance of organic solar cells (OSCs). Here, in this work, we demonstrate a random terpolymerization strategy by incorporating 1,3-bis(5-bromo-4-fluorothiophen-2-yl)-5,7-bis(2-ethylhexyl)-4H,8H-benzo[1,2-c:4,5-c']bisthiophene-4,8-dione (BFT, 30 mol%) unit with fluorinated π-bridges into the molecular backbone of PM6 and develop a terpolymer PF1. Benefiting from the strong electronegativity of fluorine atom and noncovalent interaction of F---S, the energy levels, molecular ordering, and aggregation properties of the polymer donors are precisely regulated. Notably, in the active layer film based on PF1: Y6, the π-π stacking distance can reduce to 3.51 Å, which is significantly smaller than that of PM6:Y6 (3.65 Å) and boosts the effective exciton dissociation and charge transport, thereby effectively optimize the photovoltaic properties of the related devices. As a result, the PF1:Y6-based OSCs achieved a power conversion efficiency (PCE) of up to 17.3%, which is much higher than that of the controlled OSCs based on PM6:Y6 (PCE = 16.2%). These results demonstrate high-efficiency OSCs enabled by regulating molecular aggregation via terpolymerization strategy.

14 SOLAR ENERGY↗
DOE OSTI2023

Impact of fluorination on Li + solvation and dynamics in ionic liquid-hydrofluoroether locally concentrated electrolytes

The thermal, physical, structural, and transport properties of ionic liquid (IL) electrolytes based on n-methyl-n-butylpyrrolidinium bis(trifluoromethanesulfonyl)imide [PYR14][TFSI] and Li-salts of lithium (nonafluorobutane)(trifluoromethanesulfonyl)imide [Li][IM14] and [Li][TFSI] (0 ≤ x Li ≤ 0.3), with addition of 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) (0 ≤ x TTE ≤ 0.45) were studied. While [IM14] increases glass transition, TTE improves conductivity over a wider liquidus range. Li + is solvated primarily by [TFSI] with some contribution by [IM14]. However, both 7 Li- 19 F HOESY NMR and spatial distribution functions (SDFs) derived from molecular dynamics (MD) indicate short contacts between the fluorines of TTE and Li + . This is a result of tighter anion-solvated Li + without aggregation of the Li + solvates, consistent with Raman measurements, thus confirming the existence of fluorous domains in the bulk which leads to improved fluidity and a Li + diffusivity of 1.26 x 10 –12 m 2 /s at 0 °C (x Li = 0.20) with a Li + transference of 0.16. Improved transport properties translated to a higher capacity of the TTE/IL electrolyte in a Li||LiFePO 4 half-cell with 95mAh/g at 0.1C, compared to the IL electrolyte without TTE (60 mAh/g). Furthermore, this study demonstrates the tunability of solvation and transport properties in IL electrolytes by asymmetric fluorinated anions and hydrofluoroether co-solvents for low temperature Li-ion batteries.

25 ENERGY STORAGE↗
DOE OSTI2021

High-performance multiblock PEMs containing a highly acidic fluorinated-hydrophilic domain for water electrolysis

The present paper describes the design and evaluation of novel hydrophilic–hydrophobic poly(arylene ether sulfone) (PAES) multiblock copolymers for their synergistic effects upon transport properties and their potential use in proton exchange membrane water electrolysis. The multiblock copolymers are prepared via a coupling reaction between (i) a hydrophilic segment consisting of a disulfonated quinone fluorinated biphenyl group that contains fluorine moieties next to the sulfonated groups to increase the acidity, and (ii) hydrophobic segments composed of non-sulfonated biphenyl sulfone to provide dimensional stability. Two different lengths (molecular weights; 5k and 10k, where k represents 10 3 g mol -1 ) of hydrophobic segments are used to investigate the effects of the membrane properties compared with those of Nafion® and PAES random copolymer (i.e., BPSH40). Atomic force microscopy images of the BPSH40 and multiblock membranes are shown to agree closely with a mesoscale simulation, thus confirming the importance of the morphological effect upon the transport properties. Furthermore, the multiblock copolymer with a higher proportion of hydrophilic segments (10 k–5k) was shown to provide enhanced performance (3.41 A cm -2 at 1.9 V) compared to the multiblock copolymer with equal proportions of hydrophilic and hydrophobic segments (10 k–10 k) due to the greater continuity of nano-sized ionic channels.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗