Surface complexes formed by monohydric alcohols on lithium

The He(I) photoelectron spectra of clean polycrystalline evaporated lithium films exposed to ethanol (g), n-propanol (g), and n-butanol (g) in UHV are reported. The formation of alkoxy-type surface species RO/Li (surf), at subsaturation coverages is indicated from the spectra in each case. No evidence for decomposition of the RO/Li (surf) complexes at room temperature was found. Reactivity was not indicated on exposure of clean lithium to 100 L or more of NH₃, diethylether, N₂, CO, or ethylene. Interpretation of the spectra was supported through ab initio molecular orbital calculations for models of the type RO/Li_nH_m (4? _n ?9, m = 0 or 1) as well as LiOCH₃ and LiOCH₂CH₃. Calculations including geometric variations of the methoxy group relative to the faces of fixed clusters of lithium atoms were used to locate sites of minimum energy. On the (110) face, oxygen is above a 3-atom hollow formed by two pair of near neighbor lithium atoms and one pair of next near neighbor lithium atoms. The OC direction is normal to the plane of the lithiums. On (100) the O forms a bridge between pairs of near neighbor lithiums 3.509 Å apart while on (111) oxygen forms a bridge between near neighbor lithiums 3.03 Å apart. In these bridges the OC direction is normal to the LiLi axis.     

Ab initio calculations of endo-and exohedral C60 fullerene complexes with Li+ ion and the endohedral C60 fullerene complex with Li2 dimer

The results of ab initio Hartree-Fock calculations of endo-and exohedral C₆₀ fullerene complexes with the Li⁺ ion and Li₂ dimer are presented. The coordination of the Li⁺ ion and the Li₂ dimer in the endohedral complexes and the coordination of Li⁺ ion in the exohedral complex of C₆₀ fullerene are determined by the geometry optimization using the 3–21G basis set. In the endohedral Li⁺C₆₀ complex, the Li⁺ ion is displaced from the center of the C₆₀ cage to the centers of carbon hexa-and pentagons by 0.12 nm. In the Li₂ dimer encapsulated inside the C₆₀ cage, the distance between the lithium atoms is 0.02 nm longer than that in the free molecule. The calculated total and partial one-electron densities of states of C₆₀ fullerene are in good agreement with the experimental photoelectron and X-ray emission spectra. Analysis of one-electron density of states of the endohedral Li⁺@C₆₀ complex indicates an ionic bonding between the Li atoms and the C₆₀ fullerene. In the Li⁺C₆₀ and Li⁺@C₆₀ complexes, there is a strong electrostatic interaction between the Li⁺ ion and the fullerene.     

Theoretical study of the toroidal forms of carbon and related endohedral complexes with lithium

The atomic and electron structures of toroidal carbon molecules (C₂₄₀ and two C₁₂₀ isomers) and related endohedral complexes with lithium (Li₂@C_n and Li₄@C_n) were theoretically studied using both nonempirical (3–21G basis set) and semiempirical (MNDO) calculation schemes. For the metal-containing compounds, the behavior of lithium atoms embedded into internal cavities of the carbon framework was studied using methods of molecular dynamics. It is demonstrated that the structure of electron levels of metal-containing carbon complexes exhibits an embedded state in the forbidden band, which appears due to the presence of electrons accepted from metal atoms. The position of this embedded state and the bandgap width depend both on the initial carbon structure and on the amount of metal atoms incorporated.     

Electronic and geometric properties of alkali-C60 molecules

First-principle electronic structure calculations are carried out for M_xC ₆₀ ^q , where M = Li, Na, K and ( x , q ) = (1, 0),(1,±1),(2, 0),(3, - 1),(6, 0),(6, - 1),(12, 0) using the local density functional. The electric dipole moment for MC₆₀ agrees with the experimental results. The calculated Mulliken charge indicates that the bonding of the alkali atom with C₆₀ is mostly ionic except for lithium. The alkali atom prefers to make many bonds with the carbon atoms rather than a single bond with the neighbor carbon atom. The calculated adsorption energy suggest that the metal-metal bonding of sodiums and potassiums on C₆₀ arises for more than the six valence electrons in the alkali atoms. The lithium-lithium bond is, on the other hand, not appeared for x ? 12. The difference in the most stable geometry between lithiums and the other alkali atoms on C₆₀ comes from the covalent character of the lithium-carbon bond.     

Ion bombardment-induced decomposition of Li and Ba sulfates and carbonates studied by X-ray photoelectron spectroscopy

Radiation damage to the surfaces of lithium and barium sulfates and carbonates under 4 ke V Ar⁺ bombardment has been investigated by X-ray photoelectron Spectroscopy (XPS). Damage is readily observed at a dose of 1 × 10¹⁶ ions cm^?2 with saturation occurring over the range 2–8 × 10¹⁷ ions cm^?2. Both valence and core level XPS spectra indicate that, at the saturation dose, the basic sulfate and carbonate structures remain along with decomposition products. Both sulfur and carbon are preferentially lost from all four compounds and oxygen is preferentially lost from both Li compounds but not from the Ba compounds as a result of bombardment. The major decomposition products are the metal oxides with smaller quantities of carbides, sulfides, and SO_n^x?(n = 3,2,1) species.     

An interpretation of the Auger LVV transitions from oxides of third-row elements

The principal features in the LVV Auger spectra from the oxides of third-row elements are semi-empirically derived for the XO₄^n? species of Si, PS and Cl, and the XO₆^n? species of Mg and Al. Electron molecular orbital energies are derived from X-ray photoelectron and X-ray emission spectra; the central atom 3p electron density of states is taken from the Kβ X-ray emission. Two principal peaks, separated by ca. 14 eV, are predicted for the central atom LVV Auger spectra and are experimentally confirmed for the XO₄^n? species. Similar features are observed in published spectra for oxides of Mg and Al. These peaks correspond to central atom 3p electrons in orbitals whose energy is dominated by the atomic oxygen 2s and 2p electron levels. An examination of the total LVV line-shape shows that a self-convolution of the Kβ spectra does not reproduce the more subtle features, which are probably a result of the contributions of other electron orbitals and final-state effects. The possibility of using the LVV Auger spectra to discriminate between various oxide stoichiometries, i.e. sulfate, sulfite, etc., and between various ligand species, i.e. carbide, nitride, oxide, fluoride, is discussed.     

Kinetic performance of Li4Ti5O12 anode material synthesized by the solid-state method

Li₄Ti₅O₁₂ anode was successfully synthesized by solid-state method. X-ray diffraction and scanning electron micrographs show that Li₄Ti₅O₁₂ prepared by solid-state method has a purity phase with a uniform particle size in the range of 0.5?C1???m. Cyclic voltammogram reveals that there is a big irreversible capacity for the first cycle. Li₄Ti₅O₁₂ shows a stable cycling stability at 1?C rate. After 152 cycles, the discharge capacity is 213?mAh?g^?1, which keeps 93% of it at the second cycle. Electrochemical impedance spectroscopy shows that the resistance of charge-transfer of Li₄Ti₅O₁₂ electrode decreased with increasing the storage temperatures, and the lithium diffusion coefficient is increased with increasing the storage temperatures, revealing that the kinetics of Li⁺ and electron transfer into the electrodes were much faster at high temperature than that at low temperature. The apparent activation energy of the charge transfer and lithium diffusion can be calculated to be 33.1 and 27.3?kJ?mol^?1, respectively.     

The ionic conductivity of Li6BaLa2M2O12 with coexisting Nb and Ta on the M sites

In a view to balancing cost and lithium ion conductivity, Li₆BaLa₂Nb _x Ta_2???x O₁₂ (x?=?0–2) was prepared by solid-state reaction, and its corresponding AC impedances were tested at temperatures ranging from 20 to 250 °C in air. Li₆BaLa₂Ta₂O₁₂ exhibits the highest conductivity, 8.77?×?10^?6?S/cm, and the second highest is Li₆BaLa₂Nb₂O₁₂ with 6.69?×?10^?6?S/cm. Partial replacement of Ta with Nb cannot bestow the advantages of cost saving or the enhancement of lithium ion conductivity. X-ray diffraction patterns revealed a gradual change as an increasing amount of Nb replaces Ta in Li₆BaLa₂Nb _x Ta_2???x O₁₂ (x?=?0–2), and it is thought that the trending of Nb and Ta to rest on the crystallographic planes is different.     

Effect of doping functionalized MWCNTs on the electrochemical performances of Li<Subscript>2</Subscript>CoSiO<Subscript>4</Subscript> for lithium-ion batteries

We report the synthesis of Li₂CoSiO₄ by the sol-gel method and the preparation of a composite electrode by incorporating functionalized multi-walled carbon nanotubes (fn. MWCNTs) as conductive additive. XRD pattern of the composite confirms the structural stability of Li₂CoSiO₄ even after the addition of fn. MWCNTs. SEM images of the composite reveal the presence of conductive bridges formed by MWCNTs between the submicron-sized particles of Li₂CoSiO₄. The cyclic voltammograms of the composite cathode show redox peaks with higher current density than pure Li₂CoSiO₄ and the current density increases with increase in sweep rate. The diffusion coefficient of lithium has been improved by the addition of fn. MWCNTs from 1 × 10^?14 to 8 × 10^?14 cm²/s as calculated using Randles-Sevcik equation. The charge-discharge cycling performance of both pure Li₂CoSiO₄ and composite cathode has been discussed.     

Chloride spinels: A new group of solid lithium electrolytes

The chloride spinels Li₂MCl₄ with M = Mg, Mn, Fe and Cd show very high lithium ionic conductivity in the solid state. The ionic conductivity in the compounds under investigation was established with the help of emf measurements. The specific conductivities measured by both frequency response analysis and the four probe ac method are 1.3 Ω^?1 · cm^?1 for Li₂CdCl₄, and about 0.9Ω^?1 · cm^?1 for Li₂MnCl₄, Li₂MgCl₄, and Li₂FeCl₄ at 773 K. There are several indications that the ternary chlorides become highly disordered at elevated temperatures. Thus the Arrhenius plots, i.e. In σ · T vs 1/T-curves, exhibit significant bends, the slopes below the transition temperature being considerably higher than those above.     

Chemical diffusivity of lithium in LiyTi1+xS2

Chemical diffusivity of lithium was measured in polycrystalline Li_yTi_1+xS₂ using current—pulse relaxation technique on Li/1M LiC1O₄ in THF/Ti_1+xS₂ cell. Excess titanium of the nonstoichiometric titanium disulfide did not so much reduce the lithium diffusivity in the interlayer region as in the case of sodium. The diffusivity varied with the amount of intercalated lithium. It had a maximum value of 5 × 10^?8cm²/s for all compounds of Ti_1+xS₂ (0?x?0.13) when the calculations were based on the geometrical surface area. It was calculated as about 3 × 10^?10cm²/s using the effective surface area.     

Evolution of geometrical structures,stabilities and electronic properties of neutral and anionic Li n Cu λ (n = 1–9, λ = 0, −1) clusters: compare with pure lithium clusters

The structural evolution, stabilities, and electronic properties of copper-doped lithium Li _n Cu^λ (n?=?1–9, λ?=?0, ?1) clusters have been systematically investigated using a density functional method at PW91PW91 level. Extensive searches for ground-state structures were carried out, and the results showed the copper tends to occupy the most highly coordinated position and form the largest probable number of bonds with lithium atoms. By calculating the binding energies per atom, fragmentation energies and the HOMO-LOMO gaps, we found LiCu, Li₇Cu, LiCu^?, Li₂Cu^? and Li₈Cu^? clusters have the stronger relative stability and enhanced chemical stability. The content and pattern of frontier MOs for the most stable doped isomers were analysed to investigate the bond nature of interaction among Li and Cu atoms. The results show some σ-type and π-type bonds are formed among them, and with small admixture of the Cu d characters. To achieve a deep insight into the electron localization and reliable electronic structure information, the natural population analysis and electron localization function were performed and discussed.     

Electrochemical properties of Li[CnF2n+1BF3] as electrolyte salts for lithium-ion cells

The fundamental electrochemical properties of lithium perfluoroalkyltrifluoroborates Li[C_nF_2n+1BF₃] (n = 1∼4) were evaluated as electrolyte salts for lithium-ion battery in comparison with LiBF₄ and LiPF₆. Li[C_nF_2n+1BF₃] showed higher electrolytic conductivities than LiBF₄ in aprotic solvents. In these series, the conductivities decreased with the perfluoroalkyl group being longer, and Li[C₂F₅BF₃] exhibited a comparable conductivity to LiPF₆. The relationship between the conductivity and the anion size showed that the anion with a moderate size is in favor of obtaining high conductivities. The limiting oxidation potentials determined by linear sweep voltammetry demonstrated that Li[C_nF_2n+1BF₃] were less resistant against oxidation than LiBF₄. The HOMO energies and ionization energies of [C_nF_2n+1BF₃]⁻ calculated by ab initio molecular orbital (MO) theory and density functional theory (DFT) supported this observation, however, there was no accuracy to explain the effect of the chain length of perfluoroalkyl groups on the limiting oxidation potentials. The cell performances of a LiC₆/Li_0.5CoO₂ cell using Li[C₂F₅BF₃] were comparable to those using LiPF₆ at room temperature, however, it deteriorated at elevated temperature due to the reaction on the cathode.     

Dehydrogenation of acetylene and ethylene studied on clean and oxygen covered palladium surfaces

The interaction of acetylene and ethylene with a clean and oxygen covered Pd surface has been studied at a temperature of 473 K. The measurements were performed on a hydrogen sensitive Pd-MOS structure making it possible to obtain direct information on the dissociation of both hydrogen and oxygen containing species on a palladium surface. Desorption studies were also performed as well as ultraviolet photoelectron spectroscopy and work function measurements. The studies show that both acetylene and ethylene adsorb dissociatively at this temperature leaving mainly carbon on the surface. When an oxygen covered Pd surface is exposed to C₂H₂ or C₂H₄ carbon dioxide and water will be formed and desorb until the surface is oxygen free. In the case of acetylene the presence of preadsorbed oxygen does not block or prevent the C₂H₂ dissociation on the surface. For C₂H₄, a large preadsorbed oxygen coverage (⪆ 0.45) will have an impeding effect on the dissociation. The CO₂ desorption is oxygen coverage dependent contrary to the H₂O desorption. This is due to the fact that hydrogen has a large lateral mobility on the surface while carbon has not. Both the CO₂ and H₂O reactions are, however, due to the same type of mechanisms.     

Determination of the diffusion coefficient of lithium ions in nano-Si

The diffusion coefficients of lithium ions (D_Li⁺) in nano-Si were determined by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT). D_Li⁺ values are estimated to be ~ 10^? 12 cm² s^? 1 and exhibit a “W” type varying with the lithium concentration in silicon. Two minimum regions of D_Li⁺ (at Li_2.1 ± 0.2Si and Li_3.2 ± 0.2Si) are found, which probably result from two amorphous compositions (a-Li₇Si₃ and a-Li₁₃Si₄). Besides the two minimum regions, one maximum D_Li⁺ is observed at Li₁₅Si₄, corresponding to the crystallization of highly lithiated amorphous Li_xSi.     

Ordered phases of lithium nickelite Li<Subscript>1−<Emphasis Type="Italic">x</Emphasis>−<Emphasis Type="Italic">z</Emphasis></Subscript>Ni<Subscript>1+<Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript>

A symmetry analysis of ordering in lithium nickelite Li_1?x?zNi_1+xO₂ (Li_1?x?z□_yNi_1+xO₂) was performed with regard to the substitution of Li and Ni atoms and the occurrence of structural vacancies □ in the metal sublattice. For all the ordered phases, the k ₉ ⁽³⁾ ray of the Lifshitz {k₉} star is present in the order-disorder transition channel. This ray determines the consecutive alternation of atomic planes filled with only Ni atoms or only Li atoms and vacancies in the \([1\bar 11]_{B1} \) direction. It was shown that the rhombohedral ordered LiNiO₂ phase is formed in the defect-free lithium nickelite, whereas a family of three monoclinic Li₃□Ni₄O₈ (C2/m space group) and Li₂□Ni₃O₆ (C2/m and C2 space groups) superstructures arises as the concentration of structural vacancies increases. For all the superstructures, the order-disorder phase-transition channels were determined and the distribution functions of Li and Ni atoms have been calculated. The long-range order parameters describing each superstructure were found as functions of the Li_{1?x? z}Ni_1+xO₂ composition.     

Stoichiometric synthesis of fullerene compounds with lithium and sodium and analysis of their IR and EPR spectra

A modified method is proposed for preparing fullerene compounds with alkali metals in a solution. The compounds synthesized have the general formula Me _n C₆₀(THF)_x, where Me = Li or Na; n=1–4, 6, 8, or 12; and THF = tetrahydrofuran. The use of preliminarily synthesized additives MeC₁₀H₈ makes it possible to prepare fullerene compounds with an exact stoichiometric ratio between C ₆₀ ^n? and Me ⁺. The IR and EPR spectra of the compounds prepared are analyzed and compared with the spectra of their analogs available in the literature. The intramolecular modes T _u (1)-T _u (4) for the C ₆₀ ^n? anion are assigned. The splitting of the T _u (1) mode into a doublet at room temperature for Me _n C₆₀(THF)_x (n=1, 2, 4) compounds indicates that the fullerene anion has a distorted structure. An increase in the intensity of the T _u (2) mode, a noticeable shift of the T _u (4) mode toward the long-wavelength range, and an anomalous increase in the intensity of the latter mode for the Li₃C₆₀(THF)_x complex suggest that, in the fullerene anion, the coupling of vibrational modes occurs through the charge-phonon mechanism. The measured EPR spectra of lithium-and sodium-containing fullerene compounds are characteristic of C ₆₀ ^? anions. The g factors for these compounds are almost identical and do not depend on temperature. The g factor for the C ₆₀ ^n? anion depends on the nature of the metal and differs from the g factor for the C ₆₀ ^? anion.     

The C1Πu-X1Σg+ fluorescence of Li2 excited by ultraviolet lines of an argon ion laser

The fluorescence spectra of ⁷Li₂ and ⁶Li₂ excited by an argon ion (3511 Å) laser are analyzed. No fluorescence was observed for 3514- or 3638-Å excitation or for ⁶Li⁷Li. For the C¹Π_u-X¹Σ_g⁺ electronic transition, the spectrum of ⁷Li₂ shows R and P doublets for 0 ≤ v″ ≤ 6 and that of ⁶Li₂ consists of Q lines for 0 ≤ v″ ≤ 11. Through the assignments of these lines (a) Hsu's (Ph.D. thesis, Fordham University, 1974, unpublished) molecular constants for C state have been verified, (b) the reliability of C- and X-state constants for ⁶Li₂ derived from those of ⁷Li₂ through mass-reduced scaling has been verified, and (c) the transition moment for the C-X transition of Li₂ has been shown by comparison of the observed and calculated intensities to be roughly independent of internuclear distance in the region near R_e for the C state.     

Emission secondaire de petits agregats NipCn par des carbures de nickel

The intensities of emission of Ni_pC_n⁺(p = 1–3) and NiC_n^? secondary ions given by two alloys: Ni₃C and NiC 5% at. C, show off a saw-toothed behaviour according to the parity of the number n of carbon atoms. Maxima occur when n is odd for NiC_n⁺ ions and when n is even in the other cases (p = 2, 3; negative ions). Besides, the influence of the carbon concentration in the alloy can be observed.The alternations of NiC_n⁺ and Ni₂C_n⁺ ions can be interpreted from Pitzer and Clementi model (the clusters are supposed to be linear). Thus it can be found greater stabilities for NiC_2k+1 and Ni₂C_2k chains than for NiC_2k and Ni₂C_2k+1 chains respectively, which very well agrees with the “correspondence rule” between the emissions of different species of ions and their electronic properties.     

Electrochemical characterization on layered lithium ruthenate for electrochemical supercapacitors

Electrochemical characteristics of lithium ruthenate (Li_xRuO_2+0.5x·nH₂O) for electrochemical capacitors' electrode material were first examined in this paper by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge–discharge tests. Results show that Li_xRuO_2+0.5x·nH₂O has electrochemical capacitive characteristic within the potential range of − 0.2–0.9 V (vs. SCE) in 1 M Li₂SO₄ solution. The capacitance mainly arises from pseudo-capacitance caused by lithium ions' insertion/extraction into/out of the Li_xRuO_2+0.5x·nH₂O electrode. The specific capacitance of 391 F g^− 1 can be delivered at 1 mA charge–discharge current for Li_xRuO_2+0.5x·nH₂O electrode with an energy density of 65.7 W h kg^− 1. This material also exhibits an excellent cycling performance and there is no attenuation of capacitance over 600 cycles.