Improvement of the lithium insertion properties of Li1.1V3O8

Two Li_1.1V₃O₈ samples have been prepared by heating a sol–gel precursor at 350 °C and 650 °C, i.e. below and above the melting point, respectively. Their electrochemical lithium insertion behavior was investigated after different grinding treatments. This work shows the importance of grain morphology (size, size distribution and shape) and texture (agglomeration of smaller particles or not) on both initial capacity and cyclability. It also shows that the dissolution of a small quantity of V^III in the electrolyte occurs during the last process at 2.4 V, depending on the morphology of the compound studied. Such results were taken advantage of to optimize the morphology and texture of Li_1.1V₃O₈ in order to obtain enhanced performance.     

Engineering advanced Li1.2V3O8 composite electrodes for lithium batteries

Li_1.2V₃O₈-based electrodes with a composition of 80% w/w Li_1.2V₃O₈, 12% w/w carbon black and 8% w/w poly(methyl methacrylate) can be prepared from slurries with a solid content of 30% w/w in ethyl acetate, which is a more environmentally friendly solvent than tetrahydrofuran or N-methylpyrrolidone, by adding the ethylene carbonate plasticizer at an optimum concentration of 25% w/w of dried electrode and by using ball milling. The mixing sequence of the constituents was observed to be important. Ethylene carbonate improves dispersion of the Li_1.2V₃O₈ grains and enhances the adhesion in the dry state to the current collector. A long-term cycling capacity of 250 mAh g⁻¹ was achieved. This paper was presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15, 2007.     

7Li and 51V NMR study on Li+ ionic diffusion in lithium intercalated LixV2O5

Li_xV₂O₅ (0.4 < x < 1.4) prepared by solid-state reaction were studied by ⁷Li and ⁵¹V NMR spectroscopy. ⁷Li NMR spectra showed a narrowing of the line width in relation to Li⁺ionic diffusion. Analysis of Li_xV₂O₅ using a Debye-type relaxation model showed a low activation energy ∼0.07 eV in the sample of x = 0.4 below room temperature, and revealed a Li⁺ionic diffusion with larger activation energy ∼0.5 eV above 450 K in lithium-rich samples. The latter is ascribed to the existence of a multi-phase system comprising stable ɛ- and γ-phases, resulting from complicated phase transitions at high temperature. These shapes and shifts enable the classification of the β-, ɛ-, δ-, and γ-phases. The ionic diffusion of Li⁺ ions is discussed in relation to the complicated phase transitions.     

An investigation of lithium transport properties in V6O13 single crystals

Lithium has been incorporated into single crystals of V₆O₁₃ by coulometric titration in solid state electrochemical cells. A single phase region was identified for Li_xV₆O₁₃ between x=0 and x=0.17 at 120°C. The lithium chemical diffusion coefficient, self-diffusion coefficient, ionic conductivity and partial molar entropy have been estimated at intervals over this composition range in two specific crystallographic directions. The chemical diffusion coefficients were found to be constant in a particular crystal direction with values of 3.5 × 10^-8 cm² s^-1 and 4.9 × 10^-9 cm² s^-1 perpendicular to the (0 1 0) and (0 0 1) planes respectively.     

Raman scattering from 6Li+ and 7Li+ ions in lithium beta-alumina

Raman bands due to translational modes of ⁶Li⁺ and ⁷Li⁺ ions in beta-alumina were found in the frequency range of 340–410 cm^?1, which is much higher than expected from the corresponding values reported for other alkali-metal ions (20–100 cm^?1). Based on a model calculation, it is believed that the large shifts to higher frequencies are due to deviations of the Li⁺ ions from the mirror plane into “pocket sites” formed by oxygen ions above or below the Beevers-Ross sites     

Mössbauer effect study of Li 2 1+ Me4+Fe 6 3+ O 12 2− spinels

Mossbauer effect spectra are obtained for the cubic ferrites Li₂ Me Fe₆ O₁₂ (where Me⁴⁺ is one of the tetravalent elements Ge, Si and Ti) at 78K up to their magnetic transition temperatures. In a rather large temperature range they clearly are a broadened six lines pattern. Each spectrum is successfully analysed to two sets of magnetic hyperfine splitting Zeeman patterns with isomer shifts corresponding to ferric ions in both tetrahedral and octahedral sites. The tendency of the present non-magnetic elements to occupy the octahedral site led to an antiparallel Neel spin structure. Debye and Neel temperatures of these substituted lithium ferrites are determined and their hyperfine parameters are discussed.     

Correlation between 31P chemical shift tensor and local structure in lithium cyclohexaphosphates Li6P6O18 x 3H2O and Li6P6O18

To understand the surprising behavior between the variations of the P'-P-P" angles and the correlated variations of the O'-P-O" ones, two lithium cyclohexaphosphate compounds Li6P6O18 x 3H2O and Li6P6O18 are studied by solid state nuclear magnetic resonance (NMR) spectroscopy. The two compounds exhibit the same [P6O18]6- ring anions but with 3m or 1 internal symmetry, respectively. Such symmetries induce local distortions that are exhibited by NMR spectroscopy. One-dimensional (1D) NMR gives information on structural sites of 7Li and 31P ions and the crystallographic non-equivalencies are observed. Nevertheless, in the anhydrous compound, X-ray diffraction and NMR results do not completely agree and some discrepancy exists between the number of sites observed with the first technique and the number of lines exhibited in the NMR spectra either for 7Li or 31P nuclei. This problem is elucidated by using 2D double quantum NMR spectroscopy coupled with theoretical considerations. We find that the 31P chemical shift tensor is dependent on the deviations of the O-P-O angles from those in the regular tetrahedron. Within the same empirical model, we suggest that the surprising behavior between the variations of the P'-P-P" and the ones of the O'-P-O" is related to the overall charge on the PO4 group. We also find the positions of the isotropic lines for 7Li essentially depend on the site co-ordination of this nuclei.     

Structural and electrochemical study on Li(Li1/3Ti5/3)O4 anode material for lithium ion batteries

Chemical and electrochemical studies have shown that various titanium oxides can incorporate lithium in different ratios. Other compounds with a spinel-type structure and corresponding to the spinel oxides LiTi₂O₄ and Li₄Ti₅O₁₂ have been evaluated in rechargeable lithium cells with promising features. The spinel Li[Li_1/3Ti_5/3]O₄ [1–5] compound is a very appealing electrode material for lithium ion batteries. The lithium insertion-deinsertion process occurs with a minimal variation of the cubic unit cell and this assures high stability which may reflect into long cyclability. In addition, the diffusion coefficient of lithium is of the order of 10⁻⁸ cm²s⁻¹ [5] and this suggests fast kinetics which may reflect in high power capabilities. In this work we report a study on the kinetics and the structural properties of the Li[Li_1/3Ti_5/3]O₄ intercalation electrode carried out by: cyclic voltammetry, galvanostatic cycling and in-situ X-ray diffraction. The electrochemical characterization shows that the Li[Li_1/3Ti_5/3]O₄ electrode cycles around 1.56 V vs. Li with a capacity of the order of 130 mAhg⁻¹ which approaches the maximum value of 175 mAhg⁻¹ corresponding to the insertion of 1 equivalent per formula unit. The delivered capacity remains constant for hundred cycles confirming the stability of the host structure upon the repeated Li insertion-deinsertion process. This high structural stability has been confirmed by in situ Energy Dispersion X-ray analysis. Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.     

极端条件下6Li2O的热力学性能与电子结构

采用密度泛函理论与准谐振德拜模型研究了面心立方相的6Li2O在极端条件下的热力学性质与电子结构。结果表明: 6Li2O的热膨胀系数在任何温度下都随压强增加明显降低,但仅当压强较低(低于40 GPa)时,温度对6Li2O的热膨胀系数的影响才明显;O原子半径随压强增大而迅速降低,而随温度的变化并不明显;在低压条件下(低于40 GPa),带隙随温度的升高缓慢降低;而在高压条件下(高于40 GPa),温度对带隙宽度的影响几乎可以忽略;无论在什么温度条件下,带隙宽度均随压强的增大而迅速增加。     

极端条件下6Li2O的热力学性能与电子结构

 采用密度泛函理论与准谐振德拜模型研究了面心立方相的⁶Li₂O在极端条件下的热力学性质与电子结构。结果表明: ⁶Li₂O的热膨胀系数在任何温度下都随压强增加明显降低,但仅当压强较低(低于40 GPa)时,温度对6Li2O的热膨胀系数的影响才明显;O原子半径随压强增大而迅速降低,而随温度的变化并不明显;在低压条件下(低于40 GPa),带隙随温度的升高缓慢降低;而在高压条件下(高于40 GPa),温度对带隙宽度的影响几乎可以忽略;无论在什么温度条件下,带隙宽度均随压强的增大而迅速增加。     

Preparation and characterization of Li2CoMn3O8 thin film cathodes for high energy lithium batteries

An ion layer gas reaction (ILGAR) dip-coating process for the deposition of homogeneous spinel structured Li₂CoMn₃O₈ thin layers has been developed. Thin film cathodes for use in high-energy density lithium batteries with thicknesses of about 200 nm have been prepared. The films were found to be X-ray amorphous after preparation. After annealing at 700°C in air for 2 h, the spinel structure of Li₂CoMn₃O₈ was observed by X-ray diffraction analysis. The composition of the surface was studied by XPS, which indicated enhanced Li and Mn concentrations as a result of the rinsing process and different solubilities of the precursor salts. The electrochemical behavior was investigated by separating the annealed electrode sample from a conventional organic lithium ion-conducting electrolyte by a layer of LiPON solid electrolyte and using elemental lithium as counter electrode. A capacity of 110.8 mAh/g was observed which is related to the valence changes of Mn and Co in the spinel structure.     

Energy dependence of the 6Li + 16O elastic scattering versus that of 7Li + 16O

The European Physical Journal A - Existing data for the 6Li + 16O elastic scattering at $ E_{c.m.}=3.27$ -36.8MeV were analyzed within the optical model and coupled-reaction-channels method. The...     

Photoluminescence properties of Li6CaB3O8.5: M3+ (M3+: Dy and Sm)

Li₆CaB₃O_8.5: M³⁺ (M³⁺: Dy and Sm) phosphors were synthesized by a solution combustion synthesis. The synthesized materials were characterized by using the powder XRD. The emission and excitation spectra of these materials were measured at room temperature with a spectrofluorometer. Both Li₆CaB₃O_8.5: Dy³⁺ and Li₆CaB₃O_8.5: Sm³⁺ phosphors emit red, yellow and green light. Consequently, these materials are promising phosphors for white LEDs.     

EPR study of Dy 3 + ions in DyBa 2 Cu 3 O 6 + x

Concentrated polycrystalline DyBa₂Cu₃O_6+x compounds are studied by X-band EPR spectroscopy. A broad resonance line due to the highly anisotropic EPR spectrum of Dy³⁺ ions is identified on several specimens at low temperatures. Powder simulation of the EPR spectra complies with the ground Kramers doublet predicted by crystal field analysis of Dy³⁺ ions. Calculations of the second and fourth moments of the resonance lines due to the dipole-dipole interactions of Dy³⁺ indicate the presence of substantial exchange narrowing of the dipolar-broadened EPR linewidth. Received 3 June 2001     

Excitation function of quasi-free processes in the6Li+6Li → 3α reaction

The⁶Li+⁶Li → 3α reaction was studied at energies around the Coulomb barrier. Excitation functions of the quasi-free processes⁶Li(d,α)⁴ He with an α-particle spectator either in the target or in the beam were measured.     

NMR study of 6Li in LiNbO3

An experimental NMR study of the ⁶Li isotope in single crystals of lithium niobate has been performed, along with a computer simulation of ⁶Li NMR spectra for a crystal of congruent composition, containing defects in the cation sublattice. It is found that the mean value of the principal component of the electric field gradient tensor at the ⁶Li nuclei is 1.48 times larger than at the ⁷Li nuclei. It is surmised that there is a substantial difference in the character of the mobility of the ⁶Li and ⁷Li nuclei in the LiO₆ octahedra at room temperature. Fiz. Tverd. Tela (St. Petersburg) 40, 122–125 (January 1998)     

Electrochemical properties and structures of the mixed-valence lithium cuprates Li3Cu2O4 and Li2NaCu2O4

The electrochemical performances of Li₃Cu₂O₄ and Li₂NaCu₂O₄ as cathode materials in lithium coin type batteries have been studied. In Li₃Cu₂O₄, the copper was oxidised to the III level when cycling. The replacement of the lithium by the sodium ions in the octahedral sites in Li₂NaCu₂O₄ might have an effect on the pathway of the lithium ions during the (de)intercalations. Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.     

The first in situ 7Li NMR study of the reversible lithium insertion mechanism in disorganised carbons

We study a disordered carbon designed to be used as negative electrode in a secondary lithium battery. We perform in situ magnetic resonance, i.e. we run several electrochemical cycles inside the magnet while recording NMR spectra. We obtain simultaneous ⁷Li NMR and electrochemistry data and may thus analyse: the detailed chronology of the events, the Knight shift, the line width, the relaxation time T₁. This experimental work allows us to evidence a quasi metallic lithium, less diffusive than in metal and in graphite. The quasi metallic lithium is responsible for the very good reversible capacity, at a very low voltage. We indicate a model for the insertion/extraction of lithium in the fibers. The disordered carbon under study exhibits better qualities than graphite's for secondary battery applications. Only one drawback remains: a 0.5 V hysteresis; NMR shows that it occurs when the lasts quasi metal lithium are to be extracted. We evaluate the energy barrier.     

The solid solutions of Li2Mn4O8-Li1Fe5O8

A solid solution of (1 ?x)(Li₂Mn₄O₈)x(Li₁Fe₅O₈) for 0<x<1 has been investigated by Mössbauer spectroscopy at room temperature and at 80 K. The saturated magnetic moment has been measured forx>0.6. The results are explained by a change of site preference of the Li ion from the tetragonal (A) site atx=0 to the octahedral [B] site atx=1.