Thermodynamic Approach to Electrochemical Lithium Intercalation into Li1-δMn2O4 Electrode Prepared by Sol-Gel Method

Abstract

Electrochemical lithium intercalation into Li_1-δMn₂O₄ electrode prepared by sol-gel method was investigated from the thermodynamic view point by using galvanostatic intermittent titration technique (GITT) combined with EMF-temperature measurement. The electrode potential vs. lithium content curve was theoretically calculated with the aid of the lattice gas model based upon the Bragg-Williams approximation for the cubic spinel composed of two sub-lattices. Considering the considerable difference between both lithium contents in two sub-lattices due to the ordering of the intercalated lithium ions, the theoretical partial molar enthalpy and entropy were calculated at various lithium contents by a numerical method. From the comparison between the theoretical partial molar quantities and experimental results, the electrochemical lithium intercalation into the Li_1-δMn₂O₄ electrode was discussed in terms of the ordering of the intercalated lithium ions.     

Incorporation of Lithium into TiO2 Host and its Application in Photocatalysis

Abstract

In this work we prepared the stable photocatalyst by the incorporation of lithium into TiO₂ host. Lithium hydroxide was used as the modifier. Titanium host material was in two forms: commercial titanium dioxide (anatase. Police Chemical Factory, Poland) and titanium slurry that was slightly crystallized. The prepared materials have been characterized by XRD. FTIR and UV-Vis/DR methods. The XRD analysis showed that the main component of these samples was lithium titanate—Li₂TiO₃. The photocatalytic activity of prepared materials was tested in the photocatalytic reactions of oil and phenol decomposition in water. It was found that both oil and phenol undergo the photocatalytic decomposition over lithium-TiO₂ and the activity of these materials was higher in comparison with that of pure anatase host.     

Reactions Occurring in Gels of Lithium Tetraalkyl Borates Promoted by Supermolecular Structure of Complexes

As Li[BOR'(OR)₃] and Li[B(OR)₄] complexes, where R’ and R are alkyls of iso- and normal structure, are formed from boron alkoxides and lithium in solutions of low dielectric permittivity, they are involved in autocatalytic polyassociation to give viscoelastic systems (gels) possessing a mechanical memory [1].     

Electrochemical Doping of Single Wall Carbon Nanotubes with Lithium

Abstract

Reversible insertion of Li into purified single wall carbon nanotubes was achieved electrochemically. Galvanostatic charge-discharge and cyclic voltammetry indicated that there is no well-defined redox potential for Li insertion or removal in the nanotube lattice. The Li reversible capacity was found to be 460 mA.h/g, significantly higher than the theoretical value for graphite. In-situ X-ray diffraction revealed an irreversible loss of the 2-D triangular lattice upon doping. In-situ resistivity measurements presented a 20-fold decrease in resistance upon doping, reversible upon undoping.     

Growth and Properties of Tetragonal Tungsten Bronze Type Potassium Lithium Niobate Single Crystals

Tetragonal tungsten bronze type potassium lithium niobate single crystals with the Nb/Li ratio larger than 3 are grown by the flux pulling method in our laboratory, and it dose not crack when cooling through the paraelectric/ferroelectric phase transition. Crystal growth is studied in two orientations with growth along [100] and [001], and the latter's quality is superior to that of the former. The lattice constants are a = 1.2575 nm and c = 0.3997 nm at 298 K. A Curie temperature is about 480 ± 3°C.     

Predicted structure,thermo-mechanical properties and Li ion transport in LiAlF4 glass

Materials with the LiAlF₄ composition are of interest as protective electrode coatings in Li ion battery applications due to their high cationic conductivity. Here classical molecular dynamics calculations are used to produce amorphous model structures by simulating a quench from the molten state. These are analysed in terms of their individual pair correlation functions and atomic coordination environments. This indicates that amorphous LiAlF₄ is formed of a network of corner sharing AlF₆ octahedra. Li ions are distributed within this network, primarily associated with non-bridging fluorine atoms. The nature of the octahedral network is further analysed through intra‐ and interpolyhedral bond angle distributions and the relative populations of bridging and non-bridging fluorine ions are calculated. Network topology is considered through the use of ring statistics, which indicates that, although topologically well connected, LiAlF₄ contains an appreciable number of corner‐linked branch‐like AlF₆ chains. Thermal expansion values are determined above and below the predicted glass transition temperature of 1340 K. Finally, movement of Li ions within the network is examined with predictions of the mean squared displacements, diffusion coefficients and Li ion activation energy. Different regimes for lithium ion movement are identified, with both diffusive and sessile Li ions observed. For migrating ions, a typical trajectory is illustrated and discussed in terms of a hopping mechanism for Li transport.     

A preparation of carbon fibers using a block copolymer surfactant template and its application to anode of lithium ion batteries

Hard carbon nanofiber (HCNF) bundles were prepared using reverse hexagonal micelle (H₂) phase formed by a template of an amphiphilic block copolymer surfactant and their anode performance in lithium ion batteries was analyzed. Prepared HCNF showed a higher discharge capacity at voltage region above 0.8 V (vs. Li/Li+) than that of control carbon. Rate capability was also examined in order to demonstrate merit of the fibrous morphology of CNF, with current values corresponding to 0.1, 0.2, 0.5, 1 and 2 C rate. Prepared HCNF electrode exhibited higher rate capability than control carbon, which was attributed to morphological difference.     

Study of ion transport in Li<Subscript>2</Subscript>ZrO<Subscript>3</Subscript> solid electrolytes with different lithium isotope ratios

Lithium ionic conductivity and spin-lattice relaxation rates were measured in Li₂ZrO₃ solid electrolytes with different ⁶Li and ⁷Li ratios. It is found that single-isotope electrolytes undergo a transition to the superionic state in the temperature range of 430–450 K, accompanied by an abrupt increase in conductivity. As a result of introduction of the other type of the isotope, the conductivity jump disappears in this temperature range. The transition to the superionic state is attributed to the redistribution of lithium ions over energetically nonequivalent lattice sites.     

Czochralski Growth of Potassium Lithium Niobate Single Crystals with Low Li Content and Their Characterization

Single crystalline and crack free potassium lithium niobate (KLN) single crystals with low Li content were grown by the Czochralski method. The crystal composition can be written as K_2.60Li_1.17Nb_5.44O₁₅ (=K_2.95Li_1.33Nb_6.17O₁₇) which contain relatively fewer Li ions than ferroelectric K₃Li₂Nb₅O₁₅ crystals. All experimental results show that the deficiency of the Li ions in the KLN crystals strongly influences their physical properties. Especially, the as‐grown crystals do not indicate any signature for a ferroelectric phase transition in contrast to the ferroelectric K₃Li₂Nb₅O₁₅ crystals. However, due to ionic conduction, the temperature dependence of the dielectric constant of such KLN‐2 crystals show a broad anomaly near 300°C. In addition, the existence of proton defects can be revealed by infrared absorption spectroscopy near 3500 cm^‐1 in as‐grown crystals.     

Lattice thermal expansion of potassium lithium sulphate

Unit-cell parameters and coefficients of thermal expansion of potassium lithium sulphate have been determined accurately, as a function of temperature, by the X-ray powder diffraction method. Both the parameters ‘a’ and ‘c’ increase non-linearly with increasing temperature, the change in the ‘a’ parameter being more than that in the ‘c’ parameter. As a result, the average expansion coefficient along the c-axis is found to be very small when compared to that along the a-axis. The lattice thermal behaviour of this compound is explained in terms of the strength of the bonds along the respective directions. The diffraction pattern obtained at 435 °C was completely different from those taken at other lower temperatures, suggesting a structural change contrary to the earlier reports.     

Diaquo(1,2-dimethoxyethane)lithium tetraphenylborate

The structure of diaquo(1,2-dimethoxyethane)lithium tetraphenylborate, [Li(CH₃OCH₂-CH₂OCH₃)(H₂O)₂][BPh₄], has been determined at 293 K. The compound crystallizes in the trigonal P3(1)21 space group (a = b = 9.9760(14), c = 23.662(5)). Both the lithium and the boron sit on a twofold rotation axis. The lithium is coordinated to two water oxygens and both ether oxygens of the 1,2-dimethoxyethane group. The coordination geometry is significantly distorted from a tetrahedron by the twisting of the plane containing the two water oxygens and the lithium relative to that containing the two 1,2-dimethoxyethane oxygens and the lithium. The five-membered chelate ring formed by chelation of the 1,2-dimethoxyethane to the lithium is a twist envelope consistent with the twofold rotation axis passing through the lithium and the center of the carbon–carbon bond of the 1,2-dimethoxyethane. Hydrogen bonding between each water hydrogen and a phenyl group of the tetraphenylborate is observed and results in a linear polymeric structure.     

Lithium Electrochemical Intercalation into HOPG : Kinetics Analysis of One- and Two-Phases Domains

Abstract

Electrochemical intercalation of lithium ions into HOPG has been followed using the Galvanostatic Intermittent Titration Technique. The kinetics analysis presented discriminates one-and two-phases domains, taking also into account the observation of transient lithium deposition ensuing LiC₆ appearance.     

On the occurrence of polytypism in single crystal CdTe thin films

Cadmium telluride thin films have been found to exhibit polytypism. The polytypes are formed when the as grown amorphous CdTe thin films undergo amorphous to crystalline transformation. The transformed single crystal regions correspond to different polytypes. Besides the well known zinc blende type 3 C cubic phase and less often found wurtzite type 2 H phase, four new polytypes (5 H, 6 H, 6 R and 15 R) the only ones known to-date have been found in the present investigation. In addition to the new polytypes, a new structural variant has also been found. This has the same ‘c’ parameter as that of the 2 H phase but has its ‘a’ lattice parameter as ‘a₀ \documentclass{article}\pagestyle{empty}\begin{document}$ a_{\rm o} \sqrt {3} $\end{document}’ (a₀ being the common lattice parameter of the polytypes). A feasible mechanism making the formation of polytypes intelligible has been suggested.     

High Resolution NMR Studies of Lithium and Sodium lons at the Membrane Interface

High resolution NMR spectra of lithium-6, lithium-7 and sodium-23 in a liquid crystalline mesophase consisting of sodium decylsulfate, lithium sulfate, decanol and water have been recorded. From the quadrupole splittings of the two lithium isotopes, a ratio of the quadrupole moment (Q) of ⁷Li/⁶Li equal to 49 ± 1 was obtained. By comparing the temperature dependence of the quadrupole splittings of ⁶Li, ⁷Li and ²³Na in the same mesophase, it is apparent that lithium and sodium ions interact differently with the polar head group of the mesophase. The implication of this difference is discussed.     

Modeling of cluster formation in nonlinear optical lithium niobate crystal

The processes occurring during the formation of energetically equilibrium oxygen-octahedral clusters in the ferroelectric phase of lithium niobate (LiNbO₃) crystal, have been qualitatively modeled in dependence of the phase composition. The modeling results are compared with the data obtained within vacancy models. It is shown that the cluster structure constructed along the crystallographic Y axis is most ordered, while that constructed along the polar Z axis is least ordered. The largest spread in the ratio R = Li/Nb is observed in the direction of the Z axis.     

X-ray diffraction and EXAFS analysis of materials for lithium-based rechargeable batteries

Lithium iron phosphate LiFePO₄ (triphylite) and lithium titanate Li₄Ti₅O₁₂ are used as components of a number of active materials in modern rechargeable batteries. Samples of these materials are studied by X-ray diffraction and extended X-ray absorption fine structure (EXAFS) spectroscopy. Hypotheses about the phase composition of the analyzed samples are formulated.     

Some features relevant to switching processes in the amorphous semiconductor Si12Ge10As30Te48

The current-voltage characteristics of the amorphous semiconductor glass Si₁₂Ge₁₀As₃₀Te₄₈ have been measured under various experimenal conditions. The experimental results show that the resistance of the device in the ‘off’ state and the threshold voltage for the onset of switching action decrease with increasing the maximum current (I_p) passing through the device in the ‘on’ state, and that the threshold input power to set in the switching action is practically independent of temperature. The stability and the consistency of the device depend on the magnitude of I_p. When I_p is increased to a certain value the glass within and near the current filament between the electrodes become softened, and when it reaches a critical value the device is changed from its ‘switching-on’ state to a ‘memory’ state. All the results are in good agreement with the model that the filament formed to cause switching consists of a mixture of crystalline domains and amorphous domains with phase separations.     

Synthesis of homoleptic lanthanide amides and the crystal structure of [Li(THF)4][Y(NPh2)4]

Anhydrous LnCl₃ reacted with three equivalents of LiNPh₂ in THF to give the unexpected homoleptic lanthanide amides [Li(THF)₄][Ln(NPh₂)₄] (Ln = Sm (1), Y (2)) in high yield. The crystal structure of complex 2 has been determined by X-ray diffraction methods. It crystallizes in the orthorhombic space group Pbcn with a = 17.522(3) Å, b = 16.321(3) Å, c = 19.947(3) Å, V = 5704.4(17) ų, and D _calc = 1.231 mg/m³ for Z = 4. Complex 2 is composed of discrete [Li(THF)₄]⁺ cations and [Y(NPh₂)₄]^– anions, both of which have crystallographically imposed two-fold symmetry. To achieve steric saturation of the metal center, there are interactions between the yttrium atom and one -carbon atom of each amide ligand. The yttrium and lithium atoms both exhibit distorted tetrahedral coordination geometry.     

Polymeric metal‐organic octupolar NLO materials: lithium(I) and sodium(I) 3,5‐dinitrobenzoates

Lithium 3,5‐dinitrobenzoate (Li(dnb)) exhibits a 1D propeller chain structure of D ₃ point symmetry and the chains are trigonally assembled in the crystal under the chiral space group P 3₁21. Sodium 3,5‐dinitrobenzoate (Na(dnb)) also crystallizes in space group P 3₁21 and exhibits a 3D structure. The structure of Na(dnb) could be regarded to be similar to that of Li(dnb) if the weaker Na‐O(nitro) bonds were to be ignored. These two compounds represent rare examples of octupoles arranged in an octupolar environment and show modest powder SHG effects. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The coprecipitation of magnesium aluminium hydroxocarbonate powders from aqueous solution: Precipitate compositions and coprecipitation mechanisms

Magnesium aluminium hydroxocarbonate hydrates were coprecipitated from mixed metal nitrate solutions, at total C_M = 0.2 M and Mg/Al₂ = 1 ratio, with four sodium hydrogen carbonate-sodium carbonate solutions (of pH 8.1 to 11.5) at ambient temperature. The course of precipitation was monitored by potentiometric (pH) titration, and the compositions of the primary and final precipitates were determined by chemical analysis, infrared spectrophotometry and X-ray diffraction. Precipitation generally occurred through three stages, primary precipitation (of low CO₃ aluminium hydroxocarbonates) at low pH with evolution of carbon dioxide, their dissolution by complexing to form hydroxocarbonatoaluminate anions and then secondary precipitation of the final coprecipitate at higher pHs. The final product from coprecipitation by sodium hydrogen carbonate solution (pH 8.1) was mainly the magnesium hydroxocarbonatoaluminate ‘MAHC I’; the final products from coprecipitation by sodium hydrogen carbonate-sodium carbonate solutions (pH 9.4 and 10.3) were ‘MAHC I’/‘MAHC II’ mixture and ‘MAHC II’/‘MAHC I’ mixture whereas the final product from coprecipitation by sodium carbonate solution (pH 11.5) was a complex mixture if ‘MAHC II’ with ‘MAHC I’ and ‘MAHC III’;

• ‘MAHC I’ was probably Mg₂[Al₄(OH)₁₀(CO₃)₃] · hH₂O,
• ‘MAHC II’ was probably Mg[Al₂(OH)₄(CO₃)₂] · h H₂O whereas
• ‘MAHC III’ was probably Mg[Al₂(OH)₆CO₃] · h H₂O.