Fluorinated Layer Research Articles

Insights into a surface-modified Li(Ni0.80Co0.15Al0.05)O2 cathode by atomic layer fluorination for improved cycling behaviour.

Li(Ni0.80Co0.15Al0.05)O2 is a lithium-ion battery cathode, commercially available for more than twenty years, which is associated with high energy capacity and high energy density, with moderate power. Atomic layer fluorination (ALF) of Li(Ni0.80Co0.15Al0.05)O2 with XeF2 is performed to improve its cyclability. The ALF method aims at forming an efficient protecting fluorinated layer at the surface of the material, with a low fluorine content. Surface fluorinated Li(Ni0.80Co0.15Al0.05)O2 is characterized by X-ray diffraction, electron microscopy, 19F nuclear magnetic resonance, X-ray photoelectron spectroscopy, and galvanostatic measurements, and a fluorine content as low as 1.4 wt% is found. The presence of fluorine atoms improves the electrochemical performances of Li(Ni0.80Co0.15Al0.05)O2: cyclability, polarization and rate capability are improved. Operando infrared spectroscopy and post-mortem gas chromatography provide some insights into the origins of these improvements.

Ionic Liquid Boosting the Electrochemical Stability of a Poly(1,3-dioxolane) Gel Electrolyte for High-voltage Solid-State Lithium Batteries.

Poor interfacial contact between solid-state electrolytes and electrodes limits high-voltage performance of solid-state lithium batteries. A new gel electrolyte is proposed via in-situ polymerization, incorporating fluoroethylene carbonate (FEC) solvent and ionic liquid1-butyl-1-methylpiperidinium bis(trifluoromethylsulfonyl)imide (PP14 TFSI). This combination synergistically enhances Li ion transport, achieving a transfer number of 0.58 and improved electrochemical performance. FEC protects the Al current collectors from LiPF6 corrosion and promotes a protective interfacial layer formation. PP14 TFSI improves interfacial contact and provides stable components. An interface layer of fluorine and nitrogen composites forms, preventing side reactions. LiCoO2 ||PPE||Li cell exhibits robust cycling stability at 4.45 V, retaining ~80 % capacity after 200 cycles at room temperature with 0.2 C and 1 C rates, showing increased coulombic efficiency. NCM811||PPE||Li cell also displays exceptional cycling. In-situ polymerization and FEC-ionic liquid coordination enable high-voltage solid-state lithium metal batteries for practical use.

Plasma atomic layer etching of ruthenium with surface fluorination and ion bombardment

AbstractThe plasma atomic layer etching (ALE) process for Ru was developed with surface fluorination and ion bombardment. We employed two methods for surface fluorination: (i) fluorocarbon deposition using CHF3 or C4F8 plasmas and (ii) chemisorption and diffusion with CF4 plasma. C4F8 plasma generated a more fluorine rich fluorocarbon layer on the Ru surface compared with CHF3 plasma, and a higher etch per cycle (EPC) of 1.5 nm/cycle was achieved with C4F8 plasma, in contrast to the 0.6 nm/cycle achieved with CHF3 plasma. Moreover, chemisorption and diffusion with CF4 plasma yielded an EPC of 1.2 nm/cycle. The ALE process using CHF3 plasma shows the lowest fluorine residue and lowest surface roughness compared with the ALE process using C4F8 and CF4 plasmas.

Towards dendrite-free Zn metal batteries via formation of fluorinated interfacial layer with functional additive

Rechargeable aqueous zinc metal batteries are considered as an alternative in grid-scale energy storage since they offer several intrinsic merits that make them a promising choice including absolute safety, abundant reservoir, cost-effectiveness and sustainability, whereas the Zn anode sustained poor reversibility induced by active water-related parasitic reaction and uncontrollable Zn dendrite growth. In this work, we employed fluorophosphate ester (FEP) as functional additive for ZnSO4 aqueous electrolyte, which not only participated in the formation of protective fluorinated layer on surface of Zn electrode to facilitate the Zn2+ diffusion, but also preferentially adsorb on the Zn surface to manipulate the Zn deposition orientation. Consequently, dendrite-free Zn anode was achieved with extended cycling span of over 1800 h at 10 mA cm−2, 10 mAh cm−2 in Zn symmetric cell and appealing Coulombic efficiency up to 98.9% after 500 times of zinc plating/stripping in Zn||Cu asymmetric cell. Additionally, the FEP contained electrolyte supports full cells work when paired with MnO2 and commercial LiFePO4 cathode. This feasible strategy with electrolyte functional additive provides insightful direction in the design of interfacial layers to harvest stable Zn anodes in aqueous metal-based battery technology.

Energy Storage Performance and Dielectric Properties of Surface Fluorinated BOPP Films

Various composite films with high energy storage performance and/or dielectric strength have been fabricated. However, due to some reasons, few of them have been used in practice, and BOPP film is still regarded as the state-of-the-art capacitor dielectric film. Previous work has indicated that direct fluorination can improve the dielectric strength of BOPP films. Herein, as a continuation of previous work, the energy storage performance and basic dielectric properties of the surface fluorinated BOPP film are investigated. The charge-discharge experimental results show that the surface fluorinated BOPP sample has the maximum energy storage or release density of 5.27 or 4.43 J/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , which is 59.8% or 44.6% higher than that of the virgin BOPP sample. The dielectric measurement results indicate that the surface fluorinated BOPP sample has slightly higher dielectric constant and dielectric loss than the virgin BOPP sample. The analyses of physicochemical characteristics reveal that the 0.75 μm thick fluorinated surface layer has a high degree of fluorination. The results of the calculation based on the three-layer dielectric model and the dielectric measurements further show that the fluorinated surface layer has high dielectric constant and loss factor, similar to non-perfluoropolymers. The enhancement of energy storage performance and dielectric strength is mainly attributed to the blocking of the fluorinated layer to electron injection from the cathode, due to a 60% reduction of the interfacial electric field and a decrease in free volume of the surface layer by the fluorination.

Fluorination behavior of Y2O3-MgO nanocomposite films irradiated by CF4/O2 plasma

In this study, the Y2O3-MgO (YM) nanocomposite film was prepared using radio frequency magnetron sputtering. The microstructures, chemical compositions, and fluorination behavior of YM films were systematically investigated and compared to those of Y2O3 and MgO films. After exposure to CF4/O2 etching plasma, the surface morphology of the YM nanocomposite film exhibited uniform etching behavior and preserved its original smooth surface. Energy dispersive X-ray spectroscopy mapping and transmission electron microscopy revealed that fluorine atoms present near surface region of the YM nanocomposite film and formed a thin homogeneous fluorinated layer having an average thickness of approximately 20 nm. Furthermore, the fluorinated layer of the YM nanocomposite film did not expand with prolonged plasma exposure. These results demonstrate that the chemical stability of the fine-grained YM nanocomposite film against damage due to the suppression of surface fluorination during CF4/O2 plasma etching.

Fluorination Treatment and Nano-Alumina Concentration on the Direct Current Breakdown Performance &amp; Trap Levels of Epoxy/Alumina Nanocomposite for a Sustainable Power System

Epoxy resin is extensively used in gas insulated switches as a renewable energy coating due to its exceptional insulation, mechanical characteristics, and environmental friendliness. The higher resistivity of the epoxy resin causes numerous surface charges to accumulate on the surface of the epoxy resin as a result of carrier injection due to the high DC electric field, which may cause insulation failure of the power transmission system. In this study, various concentrations of epoxy resins blended with nano-alumina (nano-Al2O3) at 0 wt%, 1 wt%, 3 wt%, and 5 wt% were created. Afterwards, the epoxy resin and Al2O3 nanocomposites were fluorinated by utilizing a combination of F2 and N2 with a ratio of 20% F2 at 0.05 MPa while maintaining the temperature at 40 °C. In order to improve dispersion, nano- Al2O3 was treated with a silane coupling agent called γ-aminopropyltriethoxysilane (KH550). Additionally, infrared spectroscopy based on the Fourier transform was used to investigate the structure of chemical bonds. Furthermore, the changes in the molecular chains were verified by the FTIR spectra. The DC breakdown strength of epoxy resin\Al2O3 nano-composites showed that breakdown strength significantly improved after gas-phase fluorination. Moreover, 1 wt% nano- Al2O3 showed a higher breakdown strength. The fluorinated layer had a charge-suppressing effect, reducing the charge injected into the polymer matrix of the epoxy-resin matrix and increasing its DC breakdown capability. Thermally stimulated current (TSC) measurements indicate that epoxy resin’s trap energy and trap density are altered by nano- Al2O3 incorporation and fluorination treatment (gas-phase). It was also observed that introducing nano- Al2O3 at a lower concentration (e.g., 1 wt%) can hinder the growth of space charge in the polymer matrix of the epoxy resin, thus enhancing the deep traps’ energy. Furthermore, a fluorination layer containing a strong polarization of C-F bonding would seize the charge injection from electrodes, thus decreasing the conductivity and suppressing the charge injection.

Construction of PP membranes with robust interfacial stability by ALD and fluorinated grafting for high salt solution distillation

In this work, PP-TSF superhydrophobic membrane was constructed by a triple layer on the PP membrane, containing titanium layer by atomic layer deposition, silica layer by sol-gel, and fluorine layer by chemical grafting. The titanium layer worked as a transition layer, increasing the binding stability between PP and the superhydrophobic layer, the silica layer provided more hydroxyl sites for superhydrophobic modification. Meanwhile, and the fluorine layer with low surface energy was the core of the superhydrophobic property. The microstructure, porosity, and pore diameter had no significant change after modification. The contact angle of the composite membrane was up to 158o, and the rolling angle was less than 10o. The hydrophobicity, self-cleaning properties, and surface roughness are significantly improved after modification. The salt retention of the high salt (15 wt%) was consistently higher than 99 % during the 21-h vacuum membrane distillation experiment.

Photolysis of Fluorinated Graphites with Embedded Acetonitrile Using a White-Beam Synchrotron Radiation.

Fluorinated graphitic layers with good mechanical and chemical stability, polar C–F bonds, and tunable bandgap are attractive for a variety of applications. In this work, we investigated the photolysis of fluorinated graphites with interlayer embedded acetonitrile, which is the simplest representative of the acetonitrile-containing photosensitizing family. The samples were continuously illuminated in situ with high-brightness non-monochromatized synchrotron radiation. Changes in the compositions of the samples were monitored using X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The NEXAFS N K-edge spectra showed that acetonitrile dissociates to form HCN and N2 molecules after exposure to the white beam for 2 s, and the latter molecules completely disappear after exposure for 200 s. The original composition of fluorinated matrices CF0.3 and CF0.5 is changed to CF0.10 and GF0.17, respectively. The highly fluorinated layers lose fluorine atoms together with carbon neighbors, creating atomic vacancies. The edges of vacancies are terminated with the nitrogen atoms and form pyridinic and pyrrolic units. Our in situ studies show that the photolysis products of acetonitrile depend on the photon irradiation duration and composition of the initial CFx matrix. The obtained results evaluate the radiation damage of the acetonitrile-intercalated fluorinated graphites and the opportunities to synthesize nitrogen-doped graphene materials.

Ferroelectricity in strained Hf2CF2 monolayer

Low dimensional ferroelectrics are highly desired for applications and full of exotic physics. Here a functionalized MXene Hf$_2$CF$_2$ monolayer is theoretically studied, which manifests a nonpolar to polar transition upon moderate biaxial compressive strain. Accompanying this structural transition, a metal-semiconductor transition occurs. The in-plane shift of unilateral fluorine layer leads to a polarization pointing out-of-plane. Such ferroelectricity is unconventional, similar to the recently-proposed interlayer-sliding ferroelectricity but not identical. Due to its specific hexapetalous potential energy profile, the possible ferroelectric switching paths and domain walls are nontrivial, which are mediated via the metallic paraelectric state. In this sense, the metallic walls can be manipulated by reshaping the ferroelectric domains.

Optimized Electrode/Electrolyte Interface of MWCNT/SnO2 Composite through Gas-Solid Fluorination.

The benefit of enriching solid-electrolyte interface with fluorine atoms through the use of fluorinated additives into the electrolyte composition has recently gained popularity for anode materials used in secondary lithium-ion batteries. Another strategy is to provide these fluorine atoms via surface fluorination of the electrode material, particularly for multiwalled carbon nanotube (MWCNT)/SnO2-based composites where fluorination must act selectively on SnO2. Our study presents two methods of surface fluorination applied on MWCNT/SnO2, one using F2(g) and the other XeF2(s). These fluorinating agents are known for their different particle penetration depths. An ultrathin and very dense fluorinated layer achieved by the action of F2(g) allows to form a very stable interface leading to gravimetric capacities of 789 mA h g-1 after 50 cycles. A thin and porous fluorinated layer made by the action of XeF2(s) favors the formation of a new Sn-based fluorinated phase, never reported in the literature, which also stabilizes capacities over 50 cycles. In any case, the value of adding fluorine atoms to the surface of the electrode material to improve cycle stability is demonstrated.

Nonflammable functional electrolytes with all-fluorinated solvents matching rechargeable high-voltage Li-metal batteries with Ni-rich ternary cathode

A nonflammable functional electrolyte with fluoroethylene carbonate (FEC) and ethyl difluoroacetate (EFA) solvents is developed to match the rechargeable Li-metal batteries (LMBs) with LiNi0.8Co0.1Mn0.1O2 cathode (NCM811). The NCM811/Li LMBs with 1 M LiPF6-FEC/EFA electrolyte exhibit an enhanced cycling retention of 74% after 150 cycles and an average coulombic efficiency of ~99.9% at 1 C under a charging cut-off voltage of 4.4 V. In contrast, the capacity retention and average coulombic efficiency of NCM811/Li LMBs with fluorocarbonate-based electrolyte are 28% and 99.5%, and the batteries with carbonate-based electrolyte are 8% and 97.2%, respectively. This FEC/EFA-based electrolyte also shows comparable low-temperature performance to carbonate-based electrolyte and is superior to fluorocarbonate-based electrolyte. It is indicated that this all-fluorinated solvent system can facilitate the formation of a durable and highly fluorinated interfacial layer on both cathode and Li-metal anode. Especially, the FEC/EFA-based electrolyte promotes the uniform Li deposition with less Li dendrites and lower polarization in the Li-metal anode, which reduces the decomposition of the electrolyte and enables stable cycling of LMBs. This FEC/EFA-based electrolyte shows promising prospects in the application of high-performance LMBs, and it also provides a novel idea for the design of all-fluorinated high-performance electrolyte to advance the commercialization of LMBs.

Charge Transport and Trapping of Surface Modified Stator Coil Insulation of Motors

This paper presents the surface modification and charge transportation mechanism of thin polyimide films. Here, we demonstrate that the surface modification of these films, by using the fluorine gas-phase, improves the charges mitigation and, thereafter, suppress the space charges. The experimental results indicate that the thermal step current for fluorine coated films reduce significantly in comparison to pure polyimide films. The thin layer of fluorine coating helps to release the surface charge, reduce the charge injection from the electrode, provide hindrance for charges to penetrate into the bulk of the films and the higher degree of charge disappearing helps to reduce the space charge growth.

Surface Fluorination Modification and Anti-Biofouling Study of a pHEMA Hydrogel.

A poly(2-hydroxyethyl methacrylate) (pHEMA) hydrogel film was prepared by bulk polymerization. Then, it was surface modified by perfluorooctanoyl chloride to improve the anti-biofouling properties. Attenuated total reflectance-Fourier transform infrared (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDXS), and atomic force microscopy (AFM) analyses demonstrated that the uniform dense fluorinated layer had been successfully grafted onto pHEMA. The water contact angle (WCA) of the modified pHEMA film increased to 135°, while the surface energy decreased to 13.32 mN/m. The protein and bacterial adhesion properties of the modified pHEMA were decreased significantly. The in vitro cytotoxicity showed that the modified pHEMA was noncytotoxic. Thus, the fluorinated modification on the material surface was a convenient and effective method to establish a hydrophobic and anti-biofouling surface.

Plasma Etching Behavior of YOF Coating Deposited by Suspension Plasma Spraying in Inductively Coupled CHF3/Ar Plasma

Dense yttrium oxyfluoride (YOF) coating was successfully deposited by suspension plasma spraying (SPS) with coaxial feeding. After deposition for 6 min at a plasma power of 105 kW, the thickness of the YOF coating was 55 ± 3.2 µm with a porosity of 0.15% ± 0.01% and the coating rate was ~9.2 µm/min. The crystalline structure of trigonal YOF was confirmed by X-ray diffractometry (XRD). The etching behavior of the YOF coating was studied using inductively coupled CHF3/Ar plasma in comparison with those of the Al2O3 bulk and Y2O3 coating. Crater-like erosion sites and cavities were formed on the whole surface of the Al2O3 bulk and Y2O3 coating. In contrast, the surface of the YOF coating showed no noticeable difference before and after exposure to the CHF3/Ar plasma. Such high resistance of the YOF coating to fluorocarbon plasma comes from the strongly fluorinated layer on the surface. The fluorination on the surface of materials was confirmed by X-ray photoelectron spectrum analysis (XPS). Depth profiles of the compositions of Al2O3, Y2O3, and YOF samples by XPS revealed that the fluorination layer of the YOF coating was much thicker than those of Al2O3 and Y2O3. These results indicate that if the inner wall of the semiconductor process chamber is coated by YOF using SPS, the generation of contamination particles would be minimized during the fluorocarbon plasma etching process.

Surface metal valence state regulating on hematite to weaken dependence of charge transport to catalyst loading

Generally, the loading of oxygen evolution catalyst (OEC) must be carefully controlled to an extremely thin level or the photo-generated holes will mainly charge the catalyst rather than oxidizing water. To overcome the extreme sensitivity of charge transport to catalyst thickness, we proposed the iron valence state regulating on hematite to negatively shift the surface defect state, thereby suppressing the severe OEC charging. In detail, a fluorine layer (FeOxFy) was inserted between Fe2O3 and OEC (ZIF-67) to reduce the oxidation state of iron atoms, forming a case where only part of Co(II) can be oxidized (build a rapid Co(II)/Co(III) cycle). Even in the case of thicker OEC (~10 nm), Fe2O3@[email protected] exhibits increased photocurrent density of 2.56 mA cm−2 at 1.23VRHE (~170% higher than Fe2O3@ZIF-67), accompanied by a rapid decrease in sensitivity to OEC loading. Above pretreatment not only relaxed the catalyst process requirements, but also provide new insights into interfacial catalysis process.

Fluorine intercalated graphene: Formation of a two-dimensional spin lattice through pseudoatomization

A suspended layer made up of ferromagnetically ordered spins could be created between two mono/multilayer graphene through intercalation. Stability and electronic structure studies show that, when fluorine molecules are intercalated between two mono/multilayer graphene, their bonds get stretched enough ($\sim$ 1.9$-$2.0 {\AA}) to weaken their molecular singlet eigenstate. Geometrically, these stretched molecules form a pseudoatomized fluorine layer by maintaining a van der Waals separation of $\sim$ 2.6 {\AA} from the adjacent carbon layers. As there is a significant charge transfer from the adjacent carbon layers to the fluorine layers, a mixture of triplet and doublet states stabilize to induce local spin-moments at each fluorine sites and in turn form a suspended 2D spin lattice. The spins of this lattice align ferromagnetically with nearest neighbour coupling strength as large as $\sim$ 100 meV. Our finite temperature \textit {ab initio} molecular dynamics study reveals that the intercalated system can be stabilized up to a temperature of 100 K with an average magnetic moment of $\sim$ 0.6 $\mu_{B}$/F. However, if the graphene layers can be held fixed, the room temperature stability of such a system is feasible.

Synthesis and physical properties of the new iridium oxyfluoride Sr2Ir(O,F)6−δ using a topochemical reaction method

We report the synthesis of a new layered iridium oxyfluoride, $\mathrm{S}{\mathrm{r}}_{2}\mathrm{Ir}{(\mathrm{O},\mathrm{F})}_{6\ensuremath{-}\ensuremath{\delta}}$, using a topochemical fluorination method. The $c$ axis is elongated compared to that in the mother compound $\mathrm{S}{\mathrm{r}}_{2}\mathrm{Ir}{\mathrm{O}}_{4}$, because the fluorine layer is inserted into the rock-salt layer while tetragonal symmetry is preserved. Resistivity measurements for the compound show nonmetallic behavior similar to that of $\mathrm{S}{\mathrm{r}}_{2}\mathrm{Ir}{\mathrm{O}}_{4}$. In magnetization measurements, suppression of antiferromagnetic order and paramagnetic behavior was observed after topochemical fluorination. Meanwhile, muon spin relaxation (\ensuremath{\mu}SR) experiments suggest the development of antiferromagnetic spin correlation between Ir spins. Furthermore, fluorine content was estimated at 1.5 the chemical composition of the fluorinated product being $\mathrm{S}{\mathrm{r}}_{2}\mathrm{Ir}{\mathrm{O}}_{x}{\mathrm{F}}_{1.5}$ with $x=3.25$, assuming $\mathrm{I}{\mathrm{r}}^{4+}$. Suppression of magnetic order in $\mathrm{S}{\mathrm{r}}_{2}\mathrm{Ir}{(\mathrm{O},\mathrm{F})}_{6\ensuremath{-}\ensuremath{\delta}}$ is attributed to antiferromagnetic instability between $\mathrm{Ir}{\mathrm{O}}_{2}$ layers by elongation of the $c$ axis due to fluorine intercalation.

Co-guiding the dendrite-free plating of lithium on lithiophilic ZnO and fluoride modified 3D porous copper for stable Li metal anode

Lithium metal battery is considered to be the most promising energy storage technologies due to its ultra-high theoretical capacity and extremely low standard potential. However, the infinite volume change during uneven deposition/dissolution process and the growth of lithium dendrite resulting in severe capacity decay and high safety hazards, which hinders the application in next generation secondary batteries. In this paper, the three dimensional (3D) porous copper is prepared through an electrochemical etching CuZn alloy, and the pore walls are modified with lithiophilic layer of ZnO and fluorine. The as-prepared 3D Cu/ZnO/F can inhibit the growth of Li dendrite and mitigate the huge volume change of Li metal anode during cycling process, resulting in stable solid electrolyte interface (SEI) layer and electrode structure. The Li|3D Cu/ZnO/F cell can be stably cycled over 300 cycles with 98% of coulomb efficiency at 0.5 mA cm−2, 1 mAh cm−2. The synergistic effects of both ZnO and fluorine on inducing the uniform deposition of lithium by providing bonding sites can inhibit the generation of lithium dendrites and thus improve the electrochemical performance of lithium metal batteries.

Conformal fluorine coated carbon paper for an energy harvesting water wheel

Utilizing the kinetic energy of a flowing river for irrigation could be tracked back to Hellenistic and Roman periods. In modern days, hydroelectric plants are built for harvesting the kinetic energy of the flowing river. However, a large investment is required in the hydroelectric plants for maximizing the power output. Here we present a low-cost and scalable TENG (triboelectric nanogenerators) based energy harvesting water wheel (ww-TENG). The water wheel works in a sliding freestanding TENG mode which generates power from the charges flow induced by contact electrification and electrostatic induction. A conformal fluorine coated carbon paper (f-CP) was employed to form the alternate electrodes. The deposited fluorine layer provides the benefits of high affinity to attract electrons as well as hydrophobicity for water repelling. The carbon paper offers a high electrical conductivity and rough structure to form a superhydrophobic property. These features enables a large charge induction and fast water/TENG separation for maximizing the power output of the energy harvesting water wheel. A lab-scale water wheel (diameter 10 cm and width 2.5 cm) is fabricated and a maximum 5.3 μW output power was measured under 50 MΩ resistance at a linear flow velocity of 2.6 m/s. The ww-TENG was employed for charging a 10 μF capacitor to 16 V and lighting up a commercial LED light bulb. As a comparison, an electromagnetic generator (EMG) could only charge the capacitor to 2.7 V with the same period of time. The EMG obtains a high power output at low load resistance case (< 100 kΩ) while the ww-TENG generates high power when the load resistance is large (> 10 MΩ). The present ww-TENG shows great potential for harvesting the kinetic energy from flowing river and targets for the applications with large load resistance like electrostatic systems.