LiF Content Research Articles

Tris(pentafluorophenyl) borane as an electrolyte additive for LiFePO4 battery

Abstract The effects of tris(pentafluorophenyl) borane (TPFPB) additive in electrolyte at the LiFePO4 cathode on the high temperature capacity fading were investigated by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), cyclability, SEM and Fourier transform infrared (FTIR). According to the study results, tris(pentafluorophenyl) borane has the ability to improve the cycle performance of LiFePO4 at high temperature. LiFePO4 electrodes cycled in the electrolyte without the TPFPB additive show a significant increase in charge transfer resistance by EIS analysis. SEM and FTIR disclose evidence of surface morphology change and solid electrolyte interface (SEI) formation. FTIR investigation shows various functional groups are found on the cathode material surface after high temperature cycling tests. The results showed an obvious improvement of high temperature cycle performance for LiFePO4 cathode material due to the TPFPB additive. The observed improved cycling performance and improved lithium ion transport are attributed to decreased LiF content in the SEI film.

Effect of vinylene carbonate (VC) as electrolyte additive on electrochemical performance of Si film anode for lithium ion batteries

The effect of VC as electrolyte additive on the electrochemical performance of Si film anode was studied in this paper. The charge/discharge test, scanning electron microscopy (SEM), electrochemical impedance spectrum (EIS), Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to investigate the cycle performance and SEI layer of Si film anode. It was found that the SEI layer formed in VC-containing electrolyte possessed better properties. It was impermeable to electrolyte and its impedance kept almost invariant upon cycling. The presence of VC in electrolyte brought out the VC-reduced products and decreased the LiF content in SEI layer. The major components of SEI layer were similar in VC-free and VC-containing electrolytes, which contained lithium salt (e.g. ROCO 2Li, Li 2CO 3, LiF), polycarbonate and silicon oxide. It was newly found that silicon oxide could be formed in SEI layer of Si film anode due to the reaction of lithiated silicon with permeated electrolyte in both VC-free and VC-containing electrolytes.

Lithium self-diffusion in some heavy metal fluoride glasses

Li self-diffusion has been studied below T g in a series of ZrF 4–BaF 2–LaF 3–LiF glasses with LiF contents of 10, 20, and 30 mol%, respectively. The D Li ∗ values range between about 10 −12 and 10 −15 cm 2/s and increase with increasing LiF content from 10 to 20% by two orders of magnitude. The stable isotopes 6Li (enriched) and 7Li and an SNMS depth profiling were used. For the precision of the diffusion data an anhydrous vacuum deposition of the 6Li tracer on the highly reactive glass surfaces was essential. In the glass with 30 mol% LiF no Li mobility could be determined yet with the present diffusion method. The Li diffusion is discussed and it is tried to understand why it displays a differing behaviour compared to that of the Na diffusion in respective NaF-containing glasses.

Transport processes in heavy metal fluoride glasses

Na self-diffusion, Li self-diffusion, Na +–Li + ion exchange, electrical conductivity, and mechanical relaxation have been studied below T g on glasses of the system ZrF 4–BaF 2–LaF 3–AF (A=Na, Li), with A=10, 20, 30 mol%. Compared to the transport mechanism in alkali-containing silicate glasses, the mechanisms in these non-oxide glasses are anomalous. Thus the self-diffusion coefficient of Na decreases with increasing NaF content, whereas that of Li increases with increasing LiF content. Both the electrical conductivity and the Na +–Li + ion exchange reach a minimum at ≈ 20 mol% LiF, and the mechanical relaxation shows one peak for the 20 and 30 mol% LiF-glasses and two peaks for the glass with 10 mol% LiF, evidencing both a contribution of F − and Li + ions to the transport. Moreover, the presence of the three partially interacting mobile species F −, Na +, Li + obviously leads to an anionic–cationic mixed ion effect. Applying the Nernst–Einstein equation to the Li + transport in LiF-containing glasses shows that its mechanism is dissimilar to that in oxide glasses. Calculated short jump distances possibly can be interpreted as an Li + movement via energetically suitable sites near F − ions. Likewise the Nernst–Planck model, successfully applied to the ionic transport in mixed alkali silicate glasses, obviously does also not hold for the present heavy metal fluoride glasses.

Low‐Temperature Firing and Microwave Dielectric Properties of Ca[(Li1/3Nb2/3)0.84Ti0.16]O3−δ Ceramics for LTCC Applications

The effects of LiF and ZnO–B2O3–SiO2 (ZBS) glass combined additives on phase composition, microstructures, and microwave dielectric properties of Ca[(Li1/3Nb2/3)0.84Ti0.16]O3−δ (CLNT) ceramics were investigated. The LiF and ZBS glass combined additives lowered the sintering temperature of CLNT ceramics effectively from 1150° to 880°C. The main diffraction peaks of all the specimens split due to the coexistence of the non‐stoichiometric phase (A) and stoichiometric phase (B), which all possess CaTiO3‐type perovskite structures. The transformation from A into B became accelerated with the increase of LiF or ZBS content. ZBS glass restrained the volatilization of lithium salt, which greatly affected the microstructures and microwave dielectric properties. CLNT ceramics with 2 wt% LiF and 3 wt% ZBS sintered at 900°C for 2 h show excellent dielectric properties: ɛr=34.3, Q×f=17 400 GHz, and τf=−4.6 ppm/°C. It is compatible with Ag electrodes, which makes it a promising ceramic for low‐temperature cofired ceramics technology application.

Fish-Tail Effect and Irreversibility Field of (Cu, C)Ba2Ca3Cu4O x -(LiF) y Superconductor

Addition of (LiF)$_{y<0.15}$, and of proper amount of (AgO)$_{z=0.45-0.8}$ as oxidizing agent, to (Cu,C)Ba$_{2}$Ca$_{3}$Cu$_{4}$O$_{10+d}$ superconductor is useful to control and shift the doping characteristics (hole density and distribution, and level of disorder) into the region where the irreversible properties, i.e. fish-tail effect (FTE) and irreversibility field H$_{irr}$, are improved. Among notable effects are the development of the second magnetization peak with a higher amplitude J$_{c}$, max and the enhancement of H$_{irr}$ at high temperatures, above a certain value T* which depends on both y$_{LiF}$ and z$_{AgO}$. The best results are obtained for the sample with y$_{LiF}$=0.1 and z$_{AgO}$=0.73. This sample preserves its single phase Cu,C-1234 composition. The influence on the FTE and H$_{irr}$ of the interplay between doping characteristics, controlled by LiF and AgO content, is discussed.

Effect of LiF addition on the phase transition of sinterable β-spodumene precursor powders prepared by a sol-gel process

β-Spodumene (Li2O · Al2O · 4SiO2, LAS4) precursor powders were obtained through a sol-gel process using Si(OC2H5)4, Al(OC4H9)3, and LiNO3 as starting materials and LiF as a sintering aid. X-ray diffraction, scanning electron microscopy, scanning transmission electron microscopy with a wavelength dispersive spectrometer, and electron diffraction analysis were utilized to study the phase transition of the β-spodumene glass–ceramics prepared from the gel-derived precursor powders with LiF additive. For the LAS4 precursor powders containing no LiF, the only crystalline phase obtained was β-spodumene. For the pellets containing less than 4.0 wt% LiF and sintered at 1050 °C for 5 h, the crystalline phases were β-spodumene solid solution and β-eucryptite (Li2O · Al2O3 · 2SiO2, LAS2) solid solution. When the LiF content was 5.0 wt% and the sintering process was carried out at 1050 °C for 5 h, the crystalline phases were β-spodumene solid solution, β-eucryptite solid solution (triclinic), and eucryptite [rhombohedral (hex.)]. When the LiF addition attains 3.0 wt%, the fully densified grains are formed, accompanied with an increase in grain size for LiF addition. At the triple junction of grain boundaries a second phase segregates which is identified to be β-spodumene solid solution. In the sintering period of LAS4 precursor powders with LiF additive, the grains converted to β-eucryptite solid solution and β-spodumene solid solution remains at the grain boundaries.

A sintering study on the β-spodumene-based glass ceramics prepared from gel-derived precursor powders with LiF additive

Beta-spodumene (Li2O·Al2O3·4SiO2, LAS) powders were prepared by a sol-gel process using Si(OC2H5)4, Al(OC4H9)3, and LiNO3 as precursors and LiF as a sintering aid agent. Dilatometry, X-ray diffraction (XRD), scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), and electron diffraction (ED) were utilized to study the sintering, phase transformation, microstructure, and properties of the β-spodumene glass-ceramics prepared from the gel-derived precursor powders with and without LiF additives. For the LAS precursor powders containing no LiF, the only crystalline phase obtained was β-spodumene. For the pellets containing less than 4 wt pct LiF and sintered at 1050 °C for 5 hours the crystalline phases were β-spodumene and β-eucryptite (Li2O·Al2O3·2SiO2). When the LiF content was 5 wt pct and the sintering process was carried out at 1050 °C for 5 hours, the crystalline phases were β-spodumene, β-eucryptite (triclinic), and eucryptite (rhombohedral (hex.)) phases. With the LiF additive increased from 0.5 to 4 wt pct and sintering at 1050 °C for 5 hours, the open porosity of the sintered bodies decrease from 30 to 2.1 pct. The grains size is about to 4 to 5 µm when pellect LAS compact contains LiF 3 wt pct as sintered at 1050 °C for 5 hours. The grains size grew to 8 to 25 µm with a remarkable discontinuous grain growth for pellet LAS compact contain LiF 5 wt pct sintered at 1050 °C for 5 hours. Relative densities greater than 90 pct could be obtained for the LAS precursor powders with LiF > 2 wt pct when sintered at 1050 °C for 5 hours. The coefficient of thermal expansion of the sintered bodies decreased from 8.3 × 10−7 to 5.2 × 10−7/°C (25 °C to 900 °C) as the LiF addition increased from 0 to 5 wt pct.

Relaxation dynamics of charge carriers in fluoroaluminozincate glasses

We have reported relaxation dynamics of charge carriers in fluoride glasses in the system ${\mathrm{ZnF}}_{2}{\ensuremath{-}\mathrm{A}\mathrm{l}\mathrm{F}}_{3}{\ensuremath{-}\mathrm{P}\mathrm{b}\mathrm{F}}_{2}\ensuremath{-}\mathrm{L}\mathrm{i}\mathrm{F}$ for different compositions in the frequency range 10 Hz--2 MHz and in the temperature range 300--550 K. We have analyzed the experimental data in the framework of the Almond-West formula and estimated the charge carrier concentration, hopping frequency, and the frequency exponent. We have observed that both the hopping frequency and the dc conductivity exhibit a minimum as a function of LiF content and the conductivity is primarily determined by the mobility rather than the concentration of charge carriers. We have also observed that the frequency exponent is independent of temperature but depends slightly on composition.

Electric conductivity and relaxation in ZnF 2–AlF 3–PbF 2–LiF glasses

The electric conductivity of ZnF 2–AlF 3–PbF 2–LiF glasses has been studied in the frequency range 10 Hz–2 MHz and in the temperature range from 300 K to just below the glass transition temperature. The conductivity decreases with the increase in the LiF content in the composition, which results from the trapping of F − ions by Li + ions. Small values of the stretching exponent β are observed for the present glasses. The value of the decoupling index decreases with an increase in LiF content, consistent with the composition dependence of the conductivity.

Dependence of the conductivity on the concentration and the hopping frequency of charge carriers in fluoride glasses

The conductivity spectra of fluoride glasses in the system ${\mathrm{ZrF}}_{4}{\ensuremath{-}\mathrm{B}\mathrm{a}\mathrm{F}}_{2}{\ensuremath{-}\mathrm{Y}\mathrm{F}}_{2}\ensuremath{-}\mathrm{L}\mathrm{i}\mathrm{F}$ with varying LiF content has been reported at different temperatures in the frequency range 10 Hz--2 MHz. The experimental data have been analyzed in the framework of the Almond-West formalism. The concentration and hopping frequency of the charge carriers, the dc conductivity, and the activation energy have been determined from the analysis of the data. The concentration of the charge carriers is observed to be almost independent of temperature and weakly dependent on composition. Both the hopping frequency and the dc conductivity exhibit a minimum at LiF content ${x}_{\mathrm{LiF}}=0.20.$ It is observed that the charge transport in these glasses occurs by the hopping mechanism and the strong electrolyte model is applicable.

Conductivity and relaxation in ZrF 4–BaF 2–YF 3–LiF glasses: effect of substitution of BaF 2 by LiF

The dc conductivity and the conductivity relaxation of ZrF 4–BaF 2–YF 3–LiF glasses with varying BaF 2 and LiF contents have been studied in the temperature range from 300 K to just below the glass transition temperature and in the frequency range 10 Hz–2 MHz. It has been observed that the conductivity shows a minimum and the activation energy a maximum at ∼20 mol% LiF content. The glass decoupling index also shows a minimum at the same composition and has been associated with the minimum of the conductivity. The small variation of the relaxation parameter β for the low LiF content is consistent with the weak coupling model. The relaxation parameter β exhibits a minimum at a composition different from that of the conductivity, resulting from the competitive influence of Ba 2+ and Li + cations on the ionic mobility.

Electrical conductivity and conductivity relaxation in glasses

The electrical conductivity and the conductivity relaxation of the fluoride glasses in the system with LiF content ranging from 10 to 60 mol% have been investigated in the frequency range 10 Hz-2 MHz and in the temperature range from 300 K to just below the glass transition temperatures. The conductivity shows a minimum and the activation energy a maximum for 20 mol% LiF content, which is interpreted as a crossover from -dominated conductivity to -dominated conductivity at 20 mol% LiF. The glass decoupling index also shows a minimum for 20 mol% LiF, which is associated with the occurrence of the minimum for the conductivity. The conductivity relaxation parameter , however, shows a minimum for 30 mol% LiF. A structural origin has been proposed to account for this.

Ion conductivity and diffusion in ZrF 4-based fluoride glasses containing LiF (0≤ xLiF≤0.60)

Electrical and diffusion properties of two complementary series of ZrF 4-based fluoride glasses containing LiF were examined as a function of LiF content (0≤ x LiF≤0.60). The ac conductivity data have been analyzed by the complex modulus formalism and a hopping mechanism for transport is suggested. Experimental points representative of various electrical and diffusion parameters as a function of x LiF for the glasses studied are located on both sides of `master' curves. 19 F and 7 Li NMR investigations show that F − and Li + ions participate as charge carriers in the conduction mechanisms. The variation of electrical and diffusion properties with increasing x LiF have been explained by the crossing for x LiF≃0.20 from a conductivity due preferentially to F − ions to a conductivity due preferentially to Li + ions. A minimum of the decoupling index, R τ ( T g), is shown for x LiF≃0.20, in agreement with the conductivity minimum observed for the same x LiF content. Variation of the β conductivity relaxation parameter involves a minimum for x LiF≃0.35. A structural origin is proposed for such a minimum, the existence of which has been previously shown for x NaF≃0.40 in the homologous fluoride glasses containing NaF.

Electrical and structural studies of lithium fluorophosphate glasses

Two different series of glasses, xF 2: (1 − x) LiPO 3 and xLiF: (1 − x) LiPO 3, have been synthesized by fluorination of LiPO 3 and incorporation of LiF in LiPO 3 respectively. The effect of incorporation of fluorine by these two different methods in the short-range structure of phosphate glasses has been characterized using X-ray photoelectron spectroscopy (XPS), infrared and electrical studies. These results provide evidence for fluorine participation in the phosphate network. Infrared results indicate the presence of P(O, F) 4 and P 2(O, F) 7 species. XPS results show that O 1s spectrum could be deconvoluted into two peaks corresponding to the non-bridging oxygens (NBO) and bridging oxygens (BO). Similarly, the F 1s spectrum consists of two peaks, showing clearly the existence of two states of fluorine environments; the ratio of these two states varies with the fluorine content. These observations suggest that fluorine atoms interact with both cations and anions leading to both LiF and PF bonds. The number of LiF bonds increases with increasing fluorine content or LiF mole fraction. The dc conductivity increases linearly, and the activation energy decreases with the increase of LiF content. The dc conductivity and activation energy of fluorinated lithium phosphate glasses do not change as the fluorine concentration increases. The conduction properties are discussed in terms of structural modification of LiPO 3 by fluorination/incorporation of LiF. The results suggest that LiF acts both as a dopant and as a network modifier. The former is responsible for the increase of conductivity.

Effect of LiF addition on the preparation of transparent Y 2O 3 by the vacuum hot pressing method

In this experiment, the effect of LiF as sintering additive and the method of loading in the preparation of transparent Y 2O 3 were investigated, together with its spectroscopic properties. Transparent Y 2O 3 was fabricated by vacuum hot pressing of the loading stepwise in graphite dies under the following conditions: temperature, 1573 K; maximum pressure, 44 MPa; and LiF content, 1.0 mass%. It has a transmittance of 78% at 644 nm and of greater than 80% from 860 nm to 6 μm wavelength.

Influence of alkali content and alkali mixing on the chemical durability of fluorozirconate glasses

The corrosion of alkali-containing fluorozirconate glasses in water and acidic and alkaline solutions was studied with glasses of the compositions (100−x) (0.6ZrF4·0.1AlF3·0.3BaF2)· xLiF and 48ZrF4·8AlF3·24BaF2·xLiF·(20−x)NaF. The corrosion of the glasses in deionized water and 0.1 n HCl solution is mainly controlled by diffusion with an inductive period due to the passage from reaction-controlled to diffusion-controlled mechanisms, and the weight loss of glass increases with increasing LiF content in the single-alkali glasses. There was no appreciable effect of alkali mixing on the corrosion of glasses in deionized water and 0.1 n HCl solution. The glasses exhibited good stability in alkaline solution. The weight loss due to corrosion of the glasses in acidic buffered solution increased exponentially with increasing LiF content.

Electrical conductivity of LiF [sbnd]AlF 3[sbnd]BaNbOF 5 quasi-fluoride glasses

A comparative study of electrical properties of two systems of glasses xLiF (100 − x)BaNbOF 5 and xLiF (100 − x) (0.3AlF 3 · 0.7BaNbOF 5) ( x = 10−60 mol%) has been carried out as a function of LiF content. A minimum in ionic conductivity and a maximum in activation energy has been detected in both systems. It was found that, in the LiF-BaNbOF 5 binary system, the maximal activation energy and the minimal ionic conductivity occur at different LiF concentrations. By analogy with many ZrF 4-based fluoride glasses and the comparison of the influence of AlF 3 on the transport properties of the glasses with low and high LiF content, it is proposed that for the ternary system the transport properties mainly result from the contribution of mobile F − ions in the low LiF content ( ⩽ 25 mol%) region. In the high LiF concentration ( > 25 mol%) domain, the ionic conductivity is mainly governed by the migration of Li + ions. For binary systems, in the low LiF content ( ⩽ 25 mol%) region, the transport properties mainly result from the F − ions; in the range of LiF concentration between 25 and 50 mol%, both Li + and F − ions are responsible for the conduction; when the LiF concentration is higher than 50 mol%, the ionic conductivity of the glasses is mainly dominated by the migration of Li + ions.

Preparation and properties of BaNbOF 5-based quasi-fluoride glasses in the system of LiF [sbnd]AlF 3[sbnd]BaNbOF 5

Quasi-fluoride glasses have been obtained in the LiF BaNbOF 5 binary system and in the LiF AlF 3 BaNbOF 5 ternary system. The LiF content can attain 67.5 mol%. Various properties of obtained glasses, including chemical durability, thermal behavior, density, refractive index, ultraviolet-visible and infrared transmission have been determined. The relationship between some physical properties of obtained glasses and their composition have been studied. The LiF-dependence of the stability ( T c − T g)/ T g for obtained glasses has been discussed according to a random polyhedra packing structural model.

Li +, F - ionic mobility in lithium fluoride glasses prepared from thorium tetrafluoride (NMR study)

The existence of glasses containing a large amount of LiF (between 25 and 75%) within the ThF 4-LiF binary system has allowed the study of the change in transport properties with LiF content. A 7Li and 19F NMR investigation showed that Li + and F - ions are simultaneously mobile. The temperature dependence of the number of mobile F - ions was determined. In the Li-low concentration domain, transport properties result from contribution of both mobile Li + and F - ions, for high Li concentration they depend only on the Li + ratio. Glasses with high Li content have good electrical performances.