Lithium Intercalation into Graphite during Direct Contact and Anodic Polarization

Values of the diffusion coefficient for lithium in thermoexpanded graphite (TEG) are measured during cathodic intercalation from an aprotic electrolyte and during the TEG plate in contact with metallic lithium without electrolyte. In the course of cathodic intercalation, the diffusion coefficient is measured by method of galvanostatic switching-on curves. During TEG contact with lithium, the variation of x-ray diffraction pattern of TEG with time is recorded. It is established that during TEG contact with lithium the lattice spacing decreases and the characteristic size of TEG particles increases with time until the lithiation is complete and intercalate LiC₆ forms. Values of the diffusion coefficient determined by either method coincide and amount to 10^–10 cm² s^–1.     

Chronovoltammetry of electrolytic molybdenum oxides at the electrochemical intercalation/deintercalation of lithium ions

Chemical diffusion coefficients of lithium ions in processes of electrochemical intercalation/deintercalation in electrolytic molybdenum oxides and the parameter of interaction between the intercalated particles (g) have been obtained by the following methods: the galvanostatic intermittent titration technique (GITT), the potential relaxation technique after current interruption (PRT), and the potential intermittent titration technique (PITT). In the potential range 2.40–1.40 V the values of of the order of 10^–11–10^–13 cm²/s have been obtained for Mo₄O₁₁ oxide. Intercalation/deintercalation was realized in one phase when g>4.Presented at the 3rd International Meeting on Advanced Batteries and Accumulators, 16–20 June 2002, Brno, Czech Republic     

Ion and solvent transfer discrimination at a nickel hydroxide film exposed to LiOH by combined electrochemical quartz crystal microbalance (EQCM) and probe beam deflection (PBD) techniques

A combined electrochemical quartz crystal microbalance (EQCM) and probe beam deflection (PBD) instrument was used to monitor the mobile species transfers associated with the redox processes of thin (Γ100–150 nmol cm⁻²) α- and β-nickel hydroxide films exposed to aqueous LiOH solution. A comparison of the measured PBD signal with the predicted PBD profiles, calculated by temporal convolution analysis of the current and mass responses, enabled the contributions to redox switching of anion (OH⁻) and solvent (H₂O) transfers to be discriminated quantitatively. The responses from the combined instrument are reconciled in terms of H⁺ deintercalation/intercalation within the nickel hydroxide structure as OH⁻ ions enter/exit the film. Hydroxide ion movement is associated with a counterflux of water. Thin nickel hydroxide films show a gradual α→β phase transformation with continuous voltammetric cycling, especially when the films are exposed to high concentrations of electrolyte. α-Films are characterised by OH⁻ transfers that dominate the H⁺ and H₂O movements; β-films are characterised by an increased participation of water and protons to the exchange dynamics.     

Electrochemical Intercalation of Lithium Ions into Electrolytic Vanadium Pentoxide

The discharge of thin films of Li _x V₂O₅ is described by a mathematical diffusion model. The chemical diffusion coefficient for lithium ions, estimated with the model, is equal to (1.01–2.5) × 10^–11 cm²/s. As the film thickness increases, the discharge capacity at a current of 20 A/cm² tends to the calculated limiting of 3.12 C/cm². The optimum thickness of the film electrode calculated for a discharge current of 20 A/cm² is 33.4 m and agrees satisfactorily with the experimental value.     

Lithium Intercalation into Nanostructured Films Based on Oxides of Tin and Titanium

The lithium intercalation into nanostructured films of mixed tin and titanium oxides is studied. X-ray diffraction and Moessbauer spectroscopy analyses reveal that films consist of a rutile solid solution (Sn, Ti)O₂ and an amorphous tin oxide enriched with Sn²⁺ ions. The films specific capacity during the first cathodic polarization in a 1 M lithium imide solution in dioxolane is 200–700 mA h/g, of which nearly one half is the irreversible capacity. During the second cycle, the latter is 15% of that in the first cycle. As the films are thin (<1 m), their capacity does not depend on the current density at 1–80 mA/g. During the electrode cycling, the capacity decreases by 2 mA h/g each cycle. The effective lithium diffusion coefficient, determined by a pulsed galvanostatic method, is 10^–11 cm²/s; it slightly increases with the film lithiation. During the first cycle, the amorphous phase of oxides is reduced to tin metal, the solid solution (Sn, Ti)O₂ decomposes, SnO₂ disperses to become an x-ray amorphous phase, and TiO₂ precipitates as a rutile phase. Lithium reversibly incorporates into the tin metal, yielding Li _y Sn, and into a disperse SnO₂ phase, yielding Li _x SnO₂.     

Thermochemical data for n-alkylmonoamine intercalation into crystalline lamellar zirconium phenylphosphonate

Layered crystalline zirconium phenylphosphonate, Zr(O₃PC₆H₅)₂, changed its interlamellar distance of 1481 pm after intercalation of n-alkylmonoamines, CH₃---(CH₂)_n---NH₂ (n=0–6). The infrared spectra of the precursor host and the corresponding intercalated compounds presented vibrations associated with PO₃ groups in the 1163–1039 cm⁻¹ range and additional bands related to C---H stretching bands in the 2950–2850 cm⁻¹ interval were observed after amine insertion. The thermogravimetric curves showed a mass loss assigned to the phenyl group; however, the amine intercalated fraction was not quantitatively determined. A peak in the ³¹P NMR spectrum centered at −6 ppm for the host was observed. The surface area was 42.0±0.2 m² g⁻¹ and the scanning electron micrograph gave images consistent with lamellar structural features. The layered compound was calorimetrically titrated with amine in ethanol, requiring three independent operations: (i) titration of matrix with amine, (ii) matrix salvation, and (iii) dilution of the amine solution. From those thermal effects the variation in enthalpy was calculated as: −41±1.00,−33.28±0.50,−34.40±0.80,−10.40±0.40,−12.40±0.42,−16.10±0.08 and −7.0±0.04 kJ mol⁻¹, for n=0–6, respectively. The exothermic enthalpic values reflected a favorable energetic process of amine–host intercalation in ethanol. The negative Gibbs free energy results supported the spontaneity of all these intercalation reactions. The positive favorable entropic values, as carbon chain size increased, are in agreement with the free solvent molecules in the medium, as the amines are progressively bonded to the crystalline lamellar inorganic matrix at the solid/liquid interface.     

Stability of Wetting Films of F108 Triblock Copolymer Aqueous Solutions on Quartz

Wetting films of nonionic F108 triblock copolymer aqueous solutions with concentrations below the CMC containing an electrolyte (NaCl) and formed on a quartz substrate are studied. Primary thick films are disclosed to be metastable. Their temporal stability is explained by the electrostatic repulsive forces. Film thinning and transition to a stable state occur slowly at low electrolyte concentrations (C _NaCl = 10^–5 and 10^–3 M, respectively) and instantly at its high concentrations (C _NaCl = 10^–2 and 10^–1 M, respectively). The stability of thin films is explained by the steric repulsive forces.     

Electrochemical Intercalation of Lithium into Graphite in Acetonitrile Solutions: The Effect of the Anion Nature

Effect of the anion nature on the cathodic intercalation of lithium into graphite is studied. The duration of a discharge process and the capacity of Li _x C₆ electrodes increase in the row Cl^– HSO₄ ^– < ClO₄ ^– < SCN^–. The highest negative potential of an Li _x C₆ electrode is reached when lithiating in an LiSCN non-aqueous solution. X-ray diffraction and microstructure analyses confirm the presence in the electrode's upper layers of predominantly layered compounds Li _x C₆A _y , where A is anion. In deep layers, the principal intercalation product is Li _x C₆.     

Voltammetric Analysis of Iodide and Diffusion Coefficients Between 25 and 85°C

The oxidation wave of iodide in 0.075 mol-L^–1 H₂SO₄ was analyzed at 25, 40, 55, 70, and 85°C. The reversibility of the I₂/I^– system was checked using logarithmic transforms, half-wave potentials, and by studying I ^–1 = f(^–1/2). The limiting currents obtained enabled us to determine the diffusion coefficient of I^– using Newman's equation. These experimental results were compared with Nernst's limiting values. The Stokes–Einstein equation is not verified. Hydration numbers for I^– at different temperatures were established. An empirical equation is proposed to predict the evolution of diffusion coefficients in a sulfuric acid medium with temperature.     

The effect of pressure and temperature of self-diffusion coefficients in several concentrated deuterium oxide diamagnetic electrolyte solutions

The pressure dependences of the self-diffusion coefficients of deuterium oxide in 4.5m solutions of LiCl–D₂O and CsCl–D₂O (also 7m) and 3.06m CaCl₂–D₂O have been measured by the NMR spin-echo method at 30°C, 60°C, and 90°C. Shear viscosities and densities of these solutions have also been determined over the same range of experimental conditions. The experimental data show that the diffusion constantD decreases with the increasing structure-making ability of the electrolyte cation Ca⁺²>Li⁺. In contrast, the diffusion coefficient for D₂O in the 4.5 and 7m CsCl solutions is equal to that for pure D₂O at 30°C but lower at 60°C and 90°C. It has been found that the Stokes-Einstein equation relates well the diffusion coefficients to shear viscosity in these concentrated electrolyte solutions.     

AC conductance of (Co0.45Fe0.45Zr0.10)X(Al2O3)1 − X nanocomposites

The influence of the composition on the AC carrier transport of the composite films containing ferromagnetic CoFeZr nanoparticles in amorphous aluminium oxide matrix has been investigated. The films 3–5 μm in thicknesses and with variable composition 30 at.% < X < 60 at.% were sputtered on a single substrate from the compound target in the chamber with argon–oxygen gas mixture. TEM and SEM measurements and Mössbauer spectroscopy data have shown that all the studied films of (Co_0.45Fe_0.45Zr_0.10)_X(Al₂O₃)_1 − X with 30 at.% < X < 65 at.% have revealed the structure with crystalline granular metallic alloy (with particles of a few nanometers in size) and amorphous alumina. AC conductance measurements were performed over the frequency range 10²–10⁶ Hz at temperatures from 80 to 330 K. DC conductance measurements have been carried out for this temperature region also. The presence of two critical regions for the metallic fraction (X₁ = 33–40% and X₂ = 50–55%), where diagram “electric property–composition” exhibited pronounced peculiarities, has been confirmed. A qualitative structural model of nanocomposite was offered to explain this behavior. In accordance with the model, the first critical region at X₁ is associated with a shift of percolation threshold due to the formation of oxide layer on metallic nanoparticles, owing to the presence of oxygen in gas ambient during the sputtering process. The second critical region of the composition at X₂ is ascribed to the formation of percolation net of magnetic metallic nanoparticles in the dielectric amorphous alumina matrix.     

Electrochemical Synthesis of Co-intercalation Compounds in the Graphite-H<Subscript>2</Subscript>SO<Subscript>4</Subscript>-H<Subscript>3</Subscript>PO<Subscript>4</Subscript>System

Anodic oxidation of highly oriented pyrolytic graphite in an electrolyte containing concentrated sulfuric and anhydrous phosphoric acids is studied for the first time. The synthesis was carried out under galvanostatic conditions at a current I = 0.5 mA and an elevated temperature (t = 80°C). Intercalation compounds of graphite (ICG) are shown to form at all concentration ratios of H₂SO₄ and H³PO⁴ acids. The intercalation compound of step I forms in solutions containing more than 80 wt % H₂SO₄, a mixture of compounds of intercalation steps I and II forms in 60% H²SO⁴, intercalation step II is realized in the sulfuric acid concentration range from 10 to 40%, and a mixture of compounds of intercalation steps III and II is formed in 5% H₂SO₄ solutions. The threshold concentration of H₂SO₄ intercalation is ∼2%. With the decrease in active intercalate (H₂SO₄) concentration, the charging curves are gradually smoothed, the intercalation step number increases, and the potentials of ICG formation also increase. As the sulfuric acid concentration in the electrolyte changes from 96 to 40 wt %, the filled-layer thickness d _i in ICG monotonously increases from 0.803 to 0.820 nm, which apparently is associated with the greater size of phosphoric acid molecules. With further increase in H₃PO₄ concentration in solution, d _i remains unchanged. According to the results of chemical analysis, both acids are simultaneously incorporated into the graphite interplanar spacing and their ratio in ICG is determined by the electrolyte composition.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 651–655.Original Russian Text Copyright © 2005 by Leshin, Sorokina, Avdeev.     

Diffusion of Sr and Zr in BaTiO3 single crystals

The diffusion of strontium and zirconium in single crystal BaTiO₃ was investigated in air at temperatures between 1000 °C and 1250 °C. Thin films of SrTiO₃, deposited by spin coating a precursor solution and thin films of zirconium, deposited onto the sample surfaces by sputtering, were used as diffusion sources. The diffusion profiles were measured by SIMS depth profiling on a time-of-flight secondary ion mass spectrometer (ToF-SIMS). The diffusion coefficients of strontium and zirconium were given by D_Sr = 3.6 × 10^2.0±4.4 exp[−(543 ± 117) kJ mol⁻¹/(RT)] cm² s⁻¹ and D_Zr = 1.1 × 10^1.0±2.1 exp[−(489 ± 56) kJ mol⁻¹/(RT)] cm² s⁻¹. The results are discussed in terms of different diffusion mechanisms in the perovskite structure of BaTiO₃.     

The kinetics of vapor-phase nitration of cellulose 2. Nitration with nitric acid under static conditions

The regularities of vapor-phase nitration of cellulose with HNO₃ under conditions of natural convection and hindered heat removal in the absence of air were studied using the nonisothermal kinetic method. It was established that the nitration rate at the depth of conversion of 0.08 to 0.7 is described by the kinetic law d/dt =k ₁ p/(1+), wherek ₁ = 10^4.49±0.6 exp(–A/RT) s^–1 atm^–1, = 10^{–35.5±15.7}exp(B/RT),A = 36.6±3.8 kl mol^–1, andB = 203±88 kJ mol^–1. The diffusion mechanism of vapor-phase nitration of cellulose, which explains the high value of activation energies, is discussed. The effective diffusion coefficient of HNO₃ in cellulose at 25 °3.7 · 10^–7 cm² s^–1) and the activation energy of diffusion (38.3±4.2 kJ mol^–1) were estimated.For Part 1, see Ref. l.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1981–1985, August, 1996.     

Zum Selbstdiffusionskoeffizienten des Wassers im Polymer (Feststoff)-Wasser-System

Zusammenfassung Wählt man zur Beschreibung einfacher färberischer Systeme die Thermodynamik der irreversiblen Prozesse, so erhält man Gleichungen für den Diffusionsprozeß. Man hat es in diesem vereinfachten Modell mit drei unabhängigen Diffusionskoeffizienten zu tun, wobei einer davon den SelbstdiffusionskoeffizientenD von Wasser im Substrat beschreibt. Durch experimentelle Untersuchungen mittels Tracer-Technik wurdeD bei verschiedenen Polymeren in der Größenordnung von 4 · 10^–10 cm² · sec^–1 bestimmt. Dieser Befund wird durch eine parakristalline Wasserstruktur im Polymer interpretiert. Die scheinbaren AktivierungsenergienE _a für diesen Diffusionsprozeß liegen mit ca. 6 kcal · Mol^–1 etwas höher als im Wasser (4,2 kcal · Mol^–1) und sprechen dafür, daß wegen der Kleinheit des diffundierenden Teilchens die Bewegung der Kettensegmente des Polymers nicht inE _a enthalten ist.

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Summary If the thermodynamics of irreversible processes is used to describe simple dyeing systems, equations for the diffusion process are obtained. This simplified model contunius three independent diffusion coefficients, one. of them describing the self-diffusion coefficientD of water in the substrate. By means of experimental investigations using tracer technics for diverse polymersD was found to be about 4 · 10^–10 cm² · sec 1. This result is interpreted by means of a paracrystalline structure of the water in the polymer. The apparent activation energiesE _a of this diffusion process, being about 6 kcal · Mol^–1, are a little greater than in water (4,2 kcal · Mol^–1), indicating that the movement of the chain-segments of the polymer is not contained inE _a , because of the smallness of the diffusing particles.

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Mit 3 Abbildungen und 1 Tabelle     

Taylor dispersion measurements at low electrolyte concentrations. I. Tetraalkylammonium perchlorate aqueous solutions

An equipment for the determination of mutual diffusion coefficients using the Taylor's dispersion technique is described. The radius of the capillary was determined with the help of various calibration methods. Diffusion coefficients of aqueous tetraalkylammonium perchlorates, Me₄NClO₄, and Et₄NClO₄, were measured at 25°C in the concentration range 10^–3 to 5×10^–2 mol-dm^–3, and the slightly soluble Pr₄NClO₄ up to 1×10^–2 mol-dm^–3. The slope of linear plots ofD vs. is in agreement with theory, in contrast to the limiting valuesD ₀, which all deviate by about –5% from the Nernst-Hartley values.     

Comparison of the Diffusion of Aqueous Glycine Hydrochloride and Aqueous Glycine

A Taylor dispersion tube has been used to measure mutual diffusion in aqueous solutions of glycine hydrochloride at 25°C and concentrations from 0.0005 to 0.5 M. Analysis of the dispersion profiles shows that the diffusion of glycine hydrochloride (GlyHCl) produces a subtantial additional flow of hydrochloric acid that is liberated by the dissociation: GlyH⁺ + Cl^- Gly + H⁺ + Cl^-. Diffusion in this system is, therefore, a ternary process described by the equations J ₁(GlyHCl) = – D ₁₁C ₁ – D ₁₂C ₂ and J ₂(HCl) = –D ₂₁C ₁ – D ₂₂C ₂ for the coupled fluxes of total glycine hydrochloride (1) and hydrochloric acid (2) components. The ratio D ₂₁/D ₁₁ of measured diffusion coefficients indicates that up to two moles of HCl are cotransported per mole of GlyHCl. Although protonated glycine diffuses with relatively mobile Cl^– counterions, the main diffusion coefficient of glycine hydrochloride, D ₁₁, is lower than or nearly identical to the diffusion coefficient of aqueous glycine. A model for the diffusion of protonated solutes is developed to interpret this result and the large coupled flows of HCl. Diffusion coefficients are also reported for the aqueous hydrochlorides of 3- and 4-aminobenzoic acids.     

The thermal dehydration and decomposition of Ba[Cu(C2O4)2(H2O)]·5H2O

The thermal behaviour of Ba[Cu(C₂O₄)₂(H₂O)]·5H₂O in N₂ and in O₂ has been examined using thermogravimetry (TG) and differential scanning calorimetry (DSC). The dehydration starts at relatively low temperatures (about 80°C), but continues until the onset of the decomposition (about 280°C). The decomposition takes place in two major stages (onsets 280 and 390°C). The mass of the intermediate after the first stage corresponded to the formation of barium oxalate and copper metal and, after the second stage, to the formation of barium carbonate and copper metal. The enthalpy for the dehydration was found to be 311±30 kJ mol^–1 (or 52±5 kJ (mol of H₂O)^–1). The overall enthalpy change for the decomposition of Ba[Cu(C₂O₄)₂] in N₂ was estimated from the combined area of the peaks of the DSC curve as –347 kJ mol^–1. The kinetics of the thermal dehydration and decomposition were studied using isothermal TG. The dehydration was strongly deceleratory and the -time curves could be described by the three dimensional diffusion (D3) model. The values of the activation energy and the pre-exponential factor for the dehydration were 125±4 kJ mol^–1 and (1.38±0.08)×10¹⁵ min^–1, respectively. The decomposition was complex, consisting of at least two concurrent processes. The decomposition was analysed in terms of two overlapping deceleratory processes. One process was fast and could be described by the contracting-geometry model withn=5. The other process was slow and could also be described by the contracting-geometry model, but withn=2.The values ofE _a andA were 206±23 kJ mol^–1 and (2.2±0.5)×10¹⁹ min^–1, respectively, for the fast process, and 259±37 kJ mol^–1 and (6.3±1.8)×10²³ min^–1, respectively, for the slow process.Dedicated to Prof. Menachem Steinberg on the occasion of his 65th birthday     

IR spectroelectrochemical studies of Fe2V4O13, FeVO4 and InVO4 thin films obtained via sol-gel synthesis

In this paper we generalize the IR spectroscopic properties of M³⁺VO₄ (M=Fe, In) orthovanadate and Fe₂V₄O₁₃ films. The films were prepared using the sol-gel synthesis route from M³⁺ nitrates and vanadium oxoisopropoxide. The vibrational bands in the IR absorbance spectra of the films are classified in terms of terminal V-O stretching (1050–880 cm^–1), bridging V-O^...Fe and V^...O^...Fe stretching (880–550 cm^–1), mixed V-O-V deformations and Fe-O stretching (<550 cm^–1) modes. Ex situ IR spectra of films were measured after consecutive charging/discharging to various intercalation coefficients x and correlated to the current peaks in the cyclic voltammetry curves measured in 1 M LiClO₄/propylene carbonate electrolyte. We classified the ex situ IR spectra of charged/discharged films according to their vibrational band changes. The results reveal that, for small values of the intercalation coefficient, crystalline FeVO₄, InVO₄ and Fe₂V₄O₁₃ films exhibit a simultaneous decrease in the intensity of all IR bands while the band frequencies remain unaffected. For the higher intercalation levels, IR mode frequencies are shifted, signaling the presence of reduced vanadium. Further charging leads to an amorphization of the film structure, which was established from the similarity of the IR spectra of charged films with those of amorphous films prepared at lower annealing temperatures. The results confirm that ex situ IR spectroelectrochemical measurement is an effective way to assess the structural changes in films with different levels of intercalation. Electronic Publication     

Organosilicon Amidophosphates and Their Eu and Er Complexes in Solutions and Films: Spectral and Luminescence Properties

Fluorescence and fluorescence excitation spectra of phosphorus-containing organosilicon ligands O = PX₂NHR (X = NMe₂, OPh; R = CH₂CH₂CH₂Si(Oet)₃ and their Eu(III) complexes in acetonitrile solutions and in films are studied. In UV region (285–420 nm), bis(dimethylamido)triethoxysilylpropylamidophosphate (X = NMe₂) and diphenyltriethoxysilylpropylamidophosphate (X = OPh) exhibit two emission bands, whose position and intensity depend on the nature of substituents at the phosphorus atom. The Eu complexes show the ligand and the cation luminescence. The emission bands of coordinated ligands are shifted to long-wave region. The cation luminescence appears as three or four bands due to f-f transitions from the excited ⁵ D ₀ level to the lower ⁷ F _1–4 levels. The most intense transition is ⁵ D ₀ → ⁷ F ₂. The emission band in a region of 420 nm appears in solutions and films prepared from both pure ligands and their Eu(III) complexes. This band is due to luminescence of spatially crosslinked nanoparticles of sesquioxane structure. The intensity ratio of the Eu³⁺ emission bands changes when going from solutions to films, the emission intensity increases in a range of 420 nm. Films containing incorporated Er complexes with amidophosphates show intense luminescence of a matrix at 430 nm and a series of weak narrow bands due to the Er³⁺ cation at 550–700 nm.__________Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 7, 2005, pp. 550–558.Original Russian Text Copyright © 2005 by Semenov, Cherepennikova, Klapshina, B. Bushuk, S. Bushuk, Douglas.