Partial Fluorination Research Articles

A Li-Rich Fluorinated Lithium Zirconium Chloride Solid Electrolyte for 4.8 V-Class All-Solid-State Batteries.

Chloride solid-state electrolytes (SEs) represent an important advance for applications in all-solid-state batteries (ASSBs). Among various chloride SEs, lithium zirconium chloride (Li2ZrCl6) is an attractive candidate considering the high natural abundance of Zr. However, Li2ZrCl6 meets the challenge in practical ASSBs because of its limited ionic conductivity and instability when paired with high-voltage cathodes. This is a major drawback, which can result in a high internal resistance, a low capacity utilization of cathode, and poor cycle stability, especially at high voltage. Existing methods cannot achieve simultaneous enhancement on both ionic conductivity and high-voltage stability due to a trade-off between lithium-ion migration and structural stability. Here a two-pronged strategy based on partial fluorination and incorporation of lithium ions in excess of stoichiometric ratios is introduced that enables high-voltage stability while increasing ionic conductivity concurrently. The Li-rich fluorinated halide SE (Li2.3ZrCl6.1F0.2) exhibits a significant advancement in performance, with an ionic conductivity that is double that of the pristine Li2ZrCl6 and much better high-voltage stability. By leveraging Li2.3ZrCl6.1F0.2 with the LiCoO2 cathode and the Li-In anode, the all-solid-state cell exhibits a remarkable initial specific capacity (198.0 mAh g-1 at 0.1 C) and a high capacity retention (78.5% after 150 cycles) within 3.0-4.8V.

Columnar Organization of Nonalternant Fluorinated Dehydrobenzannulenes.

Two new partially fluorinated dehydrobenzannulenes have been prepared by inter- and intramolecular oxidative homocoupling of diyne precursors. These systems contain fluorinated and nonfluorinated arene rings in a desymmetrized non-alternant arrangement. Both macrocycles are roughly planar and organize into extended columns in the solid state. The assembly of these columns is mediated by the combination of dispersion interactions, slipped [π⋅⋅⋅π] stacking interactions of the perfluorinated rings with each other, and their association with the nonfluorinated rings in the molecules of the neighboring macrocycles. These results suggest that partial fluorination of dehydrobenzannulenes can serve as a versatile motif for their assembly into columnar superstructures.

INVESTIGATION OF FLUORINATED DOUBLE-WALL CARBON NANOTUBES

Experimental results of investigation of the original and fluorinated ultra-long double-walled carbon nanotubes (DWCNTs) with a length of at least 1000 μm are presented. The degree of fluoridation did not exceed 27 at.%. It has been shown that the process of fluorination of samples of double-walled carbon nanotubes deforms the outer surface of the nanotube wall although does not destroy its internal concentric structure, while the diameter of the fluorinated nanotube increases by 1.5-2 times. In addition, the fluorinated samples, which were thermochemically purified from iron particles and other forms of carbon before fluorination, demonstrated many split/cut ends of nanotubes. The effect of fluorination on the electrical properties of initial and purified samples of double-walled carbon nanotubes was studied. It was revealed that with an increase in temperature from 80 to 300 K for non-fluorinated and fluorinated purified nanotube samples, the resistivity decreases, which corresponds to the semiconductor nature of the conductivity. It was also revealed that when a sample of initial DWNT is fluorinated, a change in the nature of conductivity from semiconductor to metallic is observed. With an increase in temperature from 80 to 300 K, the resistance of the non-fluorinated sample of the original DWNTs decreased by 45%, while the resistance of the fluorinated sample increased by 11%. Despite the decrease in electrical conductivity as a result of fluorination of the purified samples, all samples remained conductors, which presumably indicates partial fluorination of the outer wall of the DWNTs while maintaining the structure of the inner wall. Thus, fluorination of double-walled carbon nanotubes with a well-aligned and concentric structure leads to the formation of fluorocarbon nanostructures, which can be promising materials for electronic nanodevices. For citation: Karaeva A.R., Khaskov M.A., Kurzhumbaev D.Zh., Kulnitskiy B.A., Mordkovich V.Z. Investigation of fluorinated double-wall carbon nanotubes. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 10. P. 38-48. DOI: 10.6060/ivkkt.20246710.4y.

Crosslinked high-performance anion exchange membranes based on poly(dibenzyl N-methyl piperidine) and pentafluorobenzoyl-substituted SEBS

The x-PDB-m-F5-SEBS membrane, which is chemically crosslinked betweenPDB and Br-Hex-m-F5-SEBS, exhibits excellent phase separation, due to the introduction of a partial fluorine group, and high ionic conductivity, together with chemical stability.

Access to NHC-Boryl Mono- and Bis-Selenide and Utility as Mild Selenium Transfer Reagent Including to the C-F Bond.

Reactions of 5-SIDipp ⋅ BH3 (5-SIDipp=1,3-bis(2,6-diisopropylphenyl)-imidazolin-2-ylidene) (1) with diphenyldiselenide provide access to 5-SIDipp-boryl mono- (5-SIDipp ⋅ BH2 SePh) (2) and bis-selenide (5-SIDipp ⋅ BH(SePh)2 ) (3). The facile cleavage of the B-Se bond makes 2 a neutral source of selenium nucleophiles in substitutions reactions with benzyl bromides, and provide access to the corresponding selenoethers. The direct transformations of one of the C(sp2 )-F bonds of C5 F5 N and C6 F5 CF3 to C-Se bonds have also been achieved by the use of 2 without employing transition-metal catalysts. While it was previously established that C6 F6 could undergo complete defluoroselenation under harsh conditions, we successfully achieved partial defluorination of C6 F6 by employing 2 as a mild selenide transfer reagent. During the formation of C-Se bonds through the cleavage of C-F bonds, the potential by-product NHC ⋅ BH2 F undergoes ring expansion of the NHC, leading to the formation of the six-membered diaazafluoroborinane (7).

A meltblown cloth reinforced partially fluorinated solid polymer electrolyte for ultrastable lithium metal batteries

Employing fluorinated solid-state polymer electrolytes (SPEs) has emerged as a promising strategy to form stable solid-electrolyte interphase (SEI) on Li metal, which can regulate the behavior of Li deposition during cycling. However, in-situ polymerization of excessively fluorinated monomers suffers from weak polymerization kinetics and a low degree of polymerization. Herein, a partially fluorinated SPEs with meltblown cloth reinforcement was proposed and synthesized via UV-curing. The partially fluorinated meltblown cloth reinforced SPE (PFMC-SPE) showed significantly improved performances due to the enhanced mechanical properties from meltblown cloth and optimized electrochemical performances from the partial fluorination strategy. The PFMC-SPE possesses both a superior room temperature ionic conductivity (1.0 mS cm−1) and a wide electrochemical stability window (up to 5 V). Furthermore, the Li//LiFePO4 cell can stably work for more than 750 cycles at 1.0 C rate with a capacities retention of 84.7% from 141.2 mAh g−1 to 119.6 mAh g−1 at 30 °C. Both employing the reliable and inexpensive meltblown cloth based separators for solid-state electrolytes and the partial fluorination strategy is very promising in developing next-generation ultrastable solid-state lithium batteries.

Ln2 F2 (OH2 )(MoO3 )2 (SeO3 )2 : Promising Multifunctional Nonlinear Optical Materials Created by Partial Fluorination Strategy under Corrosion Resistant Supercritical Reactions.

It has historically been exceedingly challenging to create physically and chemically stable lanthanide compounds with strong second harmonic generation (SHG) due to their strong preference to central symmetry. In this work, five new non-centrosymmetric lanthanide selenites, namely, Ln2 F2 (OH2 )(MoO3 )2 (SeO3 )2 (Ln = Sm, Eu, Gd, Tb and Dy), are achieved by partial fluorination of the lanthanide oxygen polyhedron. An HF corrosion resistant supercritical hydrothermal method is developed, which is a facile and universal method for HF corrosion and high-temperature high-pressure environment. The title compounds displayed a novel 3D framework composed of 1D molybdenum selenite chains bridged by Ln2 F2 O12 (OH2 ) dimers. Their powder SHG responses showed a large difference, ranging from 1.0 to 9.0 × KH2 PO4 (KDP) at 1064nm. The half-filled Gd compound exhibited very strong SHG efficiency of up to 1.2 × KTP (KTiOPO4 ) at 2050nm. Compounds Tb and Gd are the first lanthanide selenites with SHG intensity reaching KTP level, which is very rare in this system. Furthermore, these compounds can also possess excellent physicochemical stability and strong luminescence emission, indicating that they are promising multifunctional nonlinear optical materials. This work offered an effective way for design and synthesis of multifunctional and high-performant nonlinear optical materials.

Spin polarization and magnetostriction properties in superperiodic Janus twisted bilayer graphenes

The atomic and electronic structure of superperiodic vertical hybrid Janus heterostructures based on doped twisted bilayer graphenes were theoretically developed and studied using electronic structure calculations. Regularly opposed superperiodic sublattices of fluorine and aluminum adatoms were used to induce structural charge polarization, and uncompensated spin moments up to 1.05 µB per unit cell, caused by local intense transverse electric fields generated by ferromagnetically aligned spin polarization of entire lattices. It was shown that spin polarization of the heterostructures is mostly determined by partial carbon and fluorine electronic states localized in the vicinity of the Fermi level, whereas superlattices of Al adatoms mostly determine the rate of charge polarization, the symmetry, and intensity of the internal transverse electric field up to −0.018 e2/Å. It was shown that proposed heterostructures may display advanced electronic spin, entanglement and magnetostriction properties perspective for various spin- and quantum-related applications.

Structural evolution of layered oxide cathodes for spent Li–ion batteries: Degradation mechanism and repair strategy

AbstractSustainable development has long been recognized as one of the most critical issues in today's energy and environment‐conscious society. It has never been more urgent to recycle and reuse the end‐of‐life cathode materials. Here, this work systematically investigates the structure‐critical degradation mechanism of polycrystalline LiNixCoyMn1−x−yO2 (NCM), combining experimental characterization and DFT simulations. Targeting the key degradation factors, a synergistic repair strategy based on deep mechanochemical activation and heat treatment was successfully proposed to direct regenerate the degraded NCM material. Studies indicate the induction and promotion of synergistic repair technique on the reconstruction of particle morphology, the recovery of the chemical composition and crystal structure, and the favorable transformation of the impurities phase in the failed materials. In particular, the synergistic repair process induces a gradient distribution of LiF and further enables partial fluorine doping into the NCM surface, forming abundant oxygen vacancies and increasing the content of highly reactive Ni2+. Benefiting from the comprehensive treatment for the multi‐scale and multi‐form degradation behaviors, the repaired material exhibits a capacity of 176.8 mA h g−1 at 0.1 C, which is comparable to the corresponding commercial material (172.8 mA h g−1). The satisfactory capacity of the recovered cathode proves that it is an effective direct renovating strategy.

Conformational Diversity in Partially Fluorinated N‐Alkyl Pipecolic Acid Amide Derivatives

AbstractThe molecular and crystal structures of 19 N‐alkyl‐substituted pipecolamide derivatives with partial fluorination of N‐propyl and N‐butyl groups are presented. Fluorination patterns include one F‐atom at internal or terminal locations, two F‐atoms in geminal or vicinal arrangements at various positions, as well as terminal trifluoromethylation. Due to the presence of the carboxamide side chain in pipecolamide derivatives, enantiomeric fluorination patterns in the N‐alkyl group result in diastereomeric compounds, which exhibit dramatically different crystal and molecular structures. An extraordinary conformational diversity is diagnosed for the various N‐alkylpiperidine units. Structural comparisons and theoretical assessments based on extensive force field calculations provide insight into consistent conformational patterns that point to intramolecular factors as well as intermolecular modulations due to crystal packing effects.

Effects of peripheral ring fluorination on the photophysical properties of hexaarylbenzenes

Hexaarylbenzenes (HABs) exhibit interesting photophysical properties that originate from the through-space charge-transfer interactions between their six twisted peripheral aromatic rings. Although the introduction of fluorine atoms into π-conjugated structures allows one to effectively control their electron density distribution and aggregation behavior, the effects of peripheral ring fluorination on HAB properties remain underexplored. This paper describes the syntheses and photophysical properties of three unsymmetrical HABs and their symmetrical regioisomers, namely compounds belonging to 0F (no fluorine atoms on the short molecular axes of the peripheral aromatic rings), 4F (four fluorine atoms as substituents on the short molecular axes of the aromatic rings with CF3 end groups), and 8F series (four fluorine atoms on the short molecular axes of each of the peripheral aromatic rings). All the HABs exhibited blue photoluminescence both in solution and in crystalline form. Molecules in the 4F series exhibited an increase in their Stokes shift with increasing solvent polarity and featured superior intramolecular charge-transfer properties, which produced a significant redshift of the PL band of the unsymmetrical molecule compared to that of its symmetrical counterpart. It is noteworthy that the 4F series exhibited photochromic behavior, that is, an additional absorption band in the longer-wavelength region was observed upon irradiating it with 280-nm UV light, and consequently the colorless solution acquired a yellow color . Thus, the partial fluorination of the HAB scaffold (4F series) produced photochromic behavior, while its other photophysical properties were preserved.

Synthesis and characterization of novel fluorinated nitriles as non-flammable and high-voltage electrolytes for lithium/lithium-ion batteries

Current carbonate or ether electrolytes for lithium-ion batteries suffer from high flammability, poor high-potential stability or complicated synthesis protocols. Herein, we design and successfully synthesize a series of novel fluorinated nitriles bridged by ether bond between the nitrile group and fluoroalkyl moiety. The relationship between the chemical structure of fluorinated nitriles (including the length of fluoroalkyl chain, partial fluorination of terminal group, and introduction of ethylene oxide units) and corresponding properties such as viscosity, dielectric constant, ionic conductivity, electrochemical stability window, flammability, solvation ability, are investigated systematically. Using the fluorinated nitriles as the main solvents, the formulated electrolytes not only exhibit non-flammable but also promise excellent stability for lithium batteries and 4.5 V high-voltage lithium-ion batteries.

Effects of fluorination on crystal structure and electrochemical performance of antiperovskite solid electrolytes

The development of all-solid-state lithium batteries (ASSLBs) depends on exploiting solid-state electrolytes (SSEs) with high ionic conductivity and electrochemical stability. Fluorination is generally considered to be an effective strategy to improve the ionic conductivity and electrochemical stability of inorganic SSEs. Here, we report the partial fluorination of the chlorine sites in an antiperovskite, by which the orthorhombic Li2OHCl was transformed into cubic Li2OHCl0.9F0.1, resulting in a fourfold increase in ionic conductivity at 30 °C. The ab initio molecular dynamics simulations suggest that both the crystal symmetry and the anions electronegativity influence the diffusion of Li+ in the antiperovskite structure. Besides, from the perspective of experiments and calculations, it is confirmed that fluorination is a feasible method to improve the electrochemical stability of antiperovskite SSEs. The LiFePO4 | Li cell based on Li2OHCl0.9F0.1 is also assembled and exhibits stable cycle performance, which indicates that fluorination of antiperovskite SSEs is an effective way to produce high-performance SSEs for practical application of ASSLBs.

Insight into the Chemical Behaviour of Chromium in CaF2-SiO2-Al2O3-MgO Flux Applied in Aluminium-Assisted Alloying of Carbon Steel in Submerged Arc Welding

Chromium alloying of weld metal is usually accomplished via weld wire. This is done because chromium has a high affinity for oxygen and is therefore not easily transferred across the arc. The formation chromium (VI) is one of the main concerns in welding with chromium containing consumables, especially in open arc processes, and less so in SAW (submerged arc welding). This study investigates the chemical behaviour of chromium in the application of unconstrained metal powders of Al, Cr, Cu and Ti in SAW. The application of aluminium in SAW is used to control the oxygen partial pressure in the process to prevent oxidation of elements of high oxygen affinity, such as chromium. The speciation of chromium was investigated in two-dimensional (2D) and three-dimensional (3D) post-weld slag samples. In the 2D slag samples, the chromium is contained in low concentrations in the oxy-fluoride matrix phase. The 3D samples showed dome structures in which evidence of vapour formation was identified. Chromium presents as distinct chromium spots throughout the oxy-fluoride dome walls, and it is not observed as solute in the oxy-fluoride phase. Chromium presents as chromium-rich Cr-Mn-Mg-O porous particles of less than 20 µm in size, which may agglomerate into larger masses. The calculated thermochemical predominance diagrams show that the Al(l)-Al2O3(s)-AlF(g) equilibrium can maintain the partial oxygen pressure (PO2) at 10−16.5 atmosphere and the partial fluorine pressure (PF2) at 10−11.4 atmosphere at 2500 °C. Under these gas phase conditions in the arc cavity, chromium is present as metallic chromium and may subsequently vaporise as chromium metal and combine with other vaporised elements.

Fluorination of the silicon-terminated (100) diamond surface using C60F48

Fluorination of the silicon terminated (100) diamond surface under ultra-high vacuum using a molecular fluorine source (C60F48) is investigated with a combination of high resolution photoelectron spectroscopy and low energy electron diffraction. The C60F48 fluorinates the dangling bonds of the silicon-termination on contact, resulting in an inhomogeneous fluorine termination, which remains when the C60F48 is removed by a 550 °C anneal. Despite removing approximately 50% of the surface silicon in the process, the two domain (3 × 1) surface symmetry of the silicon-terminated (100) surface is retained. When exposed to ambient conditions, while some fluorine is displaced by atmosphere exposure, partial fluorination remains. While further optimsation of this process is required for fluorinating diamond in cases where homogeniety and minimised surface damage are desirable, this work demonstrates the potential of the silicon-terminated (100) diamond surface for enabling engineering of the surface properties of diamond.

Structure evolution from Fe2Ni MIL MOF to carbon confined O-doped FeNi/FeF2 via partial fluorination for improved oxygen evolution reaction

Carbon confined active phase plays a significant role in the novel catalyst materials development and fabrication. Herein, we demonstrate such a catalyst material in the form of carbon confined iron-nickel alloy/iron fluoride doped by oxygen (C/O-FeNi/FeF2) derived from the Fe2Ni MIL MOF via facile carbonization and fluorination for efficient oxygen evolution reaction (OER) in the water-splitting reaction. The structural transformation from the Fe2Ni MIL MOF to the C/O-FeNi/FeF2 is demonstrated by the spectroscopic analysis and correlated to their electrochemical catalytic performance. Because of some combined merits resulting from the carbon confined active phase, increased polarity, strong electronic effect and efficient synergism of metal and metal fluoride for the facile active phase reconstruction in this hybrid system, this catalyst exhibits many good characteristics for electrochemical measurements in terms of improved conductivity, high intrinsic activity and stability, fast catalytic kinetics, increase surface area and rapid charge transfer ability. Specifically, the C/O-FeNi/FeF2 catalysts have a low overpotential of ca. 250 mV when loaded on a glass carbon electrode to offer the current density of 10 mA cm−2 in the alkaline electrolyte for OER; and no obvious performance decay is observed in the long-term stability test conducted at different potentials. The current results will be instructive for novel carbon confined catalyst and MOF derived catalyst design and fabrication in the energy catalysis reaction.

Influence of partial fluorination on growth modes of organic molecules on amorphous silicon dioxide

We study the influence of fluorination on nucleation and growth of the organic parasexiphenyl molecule ($p$-6P) on amorphous silicon dioxide ($a\text{\ensuremath{-}}\mathrm{Si}{\mathrm{O}}_{2}$) by means of atomistically resolved classical molecular dynamics computer simulations. We use a simulation model that mimics the experimental deposition from the vapor and subsequent self-assembly onto the underlying surface. Our model reproduces the experimentally observed orientational changes from lying to upright standing configurations of the grown layers. We demonstrate that the increase in the number of fluorinated groups inside the $p$-6P leads to a smoother, layer-by-layer growth on the $a\text{\ensuremath{-}}\mathrm{Si}{\mathrm{O}}_{2}$ surface: We observe that in the first layers, due to strong molecule-substrate interactions the molecules first grow in chiral (fan-like) structures, where each consecutive molecule has a higher angle, supported by molecules lying underneath. Subsequently deposited molecules bind to the already standing molecules of the chiral structures until all molecules are standing. The growth of chiral islands is the main mechanism for growth of the fluorinated $p$-6P derivative, while the $p$-6P, due to the lower interaction with the underlying substrate, forms less chiral structures. The higher degree of chirality leads to a lower-energy barrier for step-edge crossing for the fluorinated molecules. We find that partial fluorination of the $p$-6P molecule can, in this way, significantly alter its growth behavior by modifying rough, three-dimensional growth into smooth, layer-by-layer growth. This has implications for the rational design of molecules and their functionalized forms, which could be tailored for a desired growth behavior and structure formation.

Fluorination-Enhanced Surface Stability of Disordered Rocksalt Cathodes.

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-Fx , 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.

Improvement of Thermoelectric Performance in Graphene Nanoribbon by Partial Hydrogenation and Fluorination and by Substitution

Improvement of Thermoelectric Performance in Graphene Nanoribbon by Partial Hydrogenation and Fluorination and by Substitution

Giant Second-Harmonic Generation Response and Large Band Gap in the Partially Fluorinated Mid-Infrared Oxide RbTeMo2O8F.

Strong second-harmonic generation (SHG) and a wide band gap are two crucial but often conflicting parameters that must be optimized for practical nonlinear optical (NLO) materials. We report herein the first d0-transition-metal (TM) tellurite with half of the d0-TM-octahedra partially fluorinated, namely, quinary RbTeMo2O8F, which exhibits giant SHG responses (27 times that of KH2PO4 (KDP) and 2.2 times that of KTiOPO4 (KTP) with 1064 and 2100 nm laser radiation, respectively), the largest SHG values among all reported metal tellurites. RbTeMo2O8F also possesses a large band gap (3.63 eV), a wide optical transparency window (0.34-5.40 μm), and a significant birefringence (Δn = 0.263 at 546 nm). Theoretical calculations and crystal structure analysis demonstrate that the outstanding SHG responses can be definitively attributed to the uniform alignment of the polarized [MoO5F]/[MoO6] octahedra and the seesaw-like [TeO4], and the consequent favorable summative polarization of the three distinct SHG-active polyhedra, both induced by partial fluorine substitution on the [MoO6] octahedra.