Small Lithium Research Articles

P14-07 小型リチウムイオン二次電池の発熱挙動の研究

The overvoltage resistances and the entropy changes, which are the heat sources for small lithium ion secondary batteries, have been measured by several methods. The calculated temperature rises and the heat production rates of the batteries at the discharge cycle by using the measured results were compared with the experimental temperature rises and the heat production rates. The overvoltage resistance was estimated by four kinds of measurement methods, i. e. the voltage-current characteristics of batteries at constant-current discharge, the difference between the open circuit voltage and the cell voltage, the voltage change by the 60 seconds intermittent discharge, and the AC impedance measurement. The overvoltage resistance by the voltage-current characteristics is almost the same with the one by the difference between the open circuit voltage and the cell voltage. However, in some cases the resistances by the intermittent discharge and the AC impedance are shown to be smaller than the above two methods. The entropy change ΔS measured by the temperature change of open circuit voltage is shown to agree almost with the measured ΔS by the temperature rise difference between charge and discharge cycle. The cell temperature rises and the heat production rates of the batteries calculated by the overvoltage resistances by the voltage-current characteristics, and by the difference between the open circuit voltage and the cell voltage agree well with the measured for two kinds of batteries.

Energy dependence of the stopping power of MeV 16O ions in a laser-produced plasma

The energy dependence of the stopping power of 16O ions in a laser-produced plasma target was experimentally investigated in the projectile energy range of 150–350 keV/ u. In order to produce the target plasma a Q-Switched Nd-glass laser was focused onto a small lithium hydride (LiH) pellet. The plasma electron temperature and the electron line density were 15 eV and 2×10 17 cm −2, respectively. The energy loss of 16O ions in the plasma was measured by a time-of-flight (TOF) method. We found that the stopping power in the plasma agreed with the theoretical estimation based on a modified Bohr equation with correction at low velocities. In this evaluation, the effective charge of the projectile was calculated by means of rate equations on the loss and capture of electrons. It has been also found that in this projectile energy range the stopping power of the 16O ions in the plasma still increases with decreasing projectile energy, while it decreases in cold equivalent.

Lithium Ion Implantation Effects in MgO (100)

Single crystals of MgO (100) were implanted with 10(16) (6)Li ions cm(-2) at an energy of 30 keV. After ion implantation the samples were annealed isochronally in air at temperatures up to 1200K. After implantation and after each annealing step, the defect evolution was monitored with optical absorption spectroscopy and depth-sensitive Doppler Broadening Positron Beam Analysis (PBA). A strong increase in the S-parameter is observed in the implantation layer at a depth of approximately 100 nm. The high value of the S-parameter is ascribed to positron annihilation in small lithium precipitates. The results of 2D-ACAR and X-TEM analysis show evidence of the presence of lithium precipitates. The depth distribution of the implanted (6)Li atoms was monitored with Neutron Depth Profiling (NDP). It was observed that detrapping and diffusion of (6)Li starts at an annealing temperature of 1200K.

Rechargeable batteries with aqueous electrolytes

In recent years, rechargeable batteries (RB’s) have found important new applications in rapidly expanding markets, such as portable computers (laptops), telecommunication equipment (handies), camcorders and tools. The interest in electric vehicles has continued to stimulate research on RB’s having improved specific energy. Attention has been focussed on nonaqueous battery systems, in particular on lithium batteries. Small rechargeable lithium batteries, available on the market today, show specific energies of 100–120 Wh kg −1. The upper limit surpasses those of aqueous electrolyte counterparts (nickel–cadmium or nickel–metal hydride) by a factor of 1.5–2. Is there still a future for aqueous electrolyte battery systems? This paper reviews the present status of the various RB’s with aqueous electrolytes and analyses their outlook for the future. Traditionally, lead, cadmium and iron were used as active materials in the negative electrode. In recent years, research on rechargeable zinc electrodes has been intensified. The development of metal hydride negative electrodes has resulted in RB’s with improved specific energy (60–70 Wh kg −1, under some conditions even 80 Wh kg −1). Similar values can be reached with nickel–zinc batteries, the latter having, however, a considerably lower cycle life. Rechargeable zinc–air batteries, with bifunctional air electrodes, are capable of specific energies matching those of lithium batteries. Their cycle life is, however, up to now still totally unsatisfactory. Systems with ‘mechanical recharge’ of the highly porous zinc electrodes have been tested in electric vehicles. Although the specific energy during discharge exceeded 200 Wh kg −1, this system has not gained any large scale practical acceptance. All metal–air batteries suffer, in principle, from a poor energy efficiency ( η<50%). At present, it appears unlikely that alternative negative electrode materials, such as anthraquinone, polypyrrole, or specially passivated lithium, can be adapted to permit long-term cycling in aqueous electrolytes. Regarding positive electrodes, no alternatives to lead dioxide and nickel-oxy hydroxide are in sight. Manganese dioxide electrodes tend to rapidly loose capacity during cycling. So far, active materials such as bromine, chlorine and insertion electrodes based on carbon, have not, and will probably not in the near future, see commercial use. The main advantages of aqueous electrolyte systems are low cost and ability to withstand overcharge (due to the establishment of the socalled oxygen cycle). This simplifies charging equipment. Due to high electrolyte conductivity, relatively thick electrodes can be used. Lead–acid batteries, in particular maintenance-free or sealed types, will remain ‘work horses’ in SLI and stationary (standby) applications. Large stationary redox cells may possibly find use for the storage of solar energy. Of all the aqueous systems, the metal hydride batteries might have the brightest future. Chances are good that their specific energy can be further improved. Negative and positive electrodes are both of the ‘insertion type’, thus avoiding a dissolution–redeposition step. This results in excellent cycle life. As to electric cars, aqueous–electrolyte fuel cell systems might some day become power sources being capable to beat lithium batteries with respect to specific energy and driving range.

Size and Shape Effects on Electronic Energy Levels: From Infinite to Nanoscopic Systems in Three-Dimensional Space

The size and shape effects on the electronic energy levels of a system are studied in the light of a recently proposed solvable model for the non-relativistic quantum scattering in three-dimensional space of a particle off several interactions centred at N arbitrary points. The transition from infinite to finite size is studied numerically for perfect systems, such as a massive solid, a layer and a linear chain. In particular, the case of systems with lithium atomic centres is tackled. Finally, with the more stable geometries of small lithium clusters found in the literature, the vertical ionization potential is also discussed qualitatively within the present model.

Ab initio Monte Carlo Investigations of Small Lithium Clusters

Structural and thermal properties of small lithium clusters are studied using ab initio-based Monte Carlo simulations. The ab initio scheme uses a Hartree-Fock/density functional treatment of the electronic structure combined with a jump-walking Monte Carlo sampling of nuclear configurations. Structural forms of Li8 and Li+9 clusters are obtained and their thermal properties analyzed in terms of probability distributions of the cluster potential energy, average potential energy and configurational heat capacity all considered as a function of the cluster temperature. Details of the gradual evolution with temperature of the structural forms sampled are examined. Temperatures characterizing the onset of structural changes and isomer coexistence are identified for both clusters.

Ab initio Monte Carlo Investigations of Small Lithium Clusters

Structural and thermal properties of small lithium clusters are studied using ab initio-based Monte Carlo simulations. The ab initio scheme uses a Hartree-Fock/density functional treatment of the electronic structure combined with a jump-walking Monte Carlo sampling of nuclear configurations. Structural forms of Li{sub 8} and Li{sub 9}{sup +} clusters are obtained and their thermal properties analyzed in terms of probability distributions of the cluster potential energy, average potential energy and configurational heat capacity all considered as a function of the cluster temperature. Details of the gradual evolution with temperature of the structural forms sampled are examined. Temperatures characterizing the onset of structural changes and isomer coexistence are identified for both clusters.

Static electric dipole polarizabilities of alkali clusters

We have measured the static dipole polarizability of lithium and sodium clusters (n = 1 − 22). Values measured for sodium are in agreement with previous experiments. While the polarizability per atom for sodium clusters decreases slowly as a function of the cluster size, a sharp decrease between sizes 1 and 4 is observed for lithium clusters. Experimental values are compared to Density Functional Theory (DFT/PW91) calculations. The size evolutions for sodium and lithium cluster polarizabilities are well reproduced by our calculations. The sharp decrease observed for small lithium clusters is discussed in terms of electronic density.

Ionization potentials of hypervalent LinC (2≤n≤10)

We report on a combined experimental and theoretical. investigation of the ionization potentials of small lithium monocarbide clusters. The clusters were produced by a laser vaporization source, and their ionization potentials were measured by threshold photoionization spectroscopy. The structures of the smaller clusters (n ≤ 8), which are governed by hypervalent (hyperlithiated) bonding mechanisms, were calculated by means of density functional theory. Vertical and adiabatic ionization potentials were computed and compared with the experimental data.

The role of quantum and thermal fluctuations upon properties of lithium clusters

The impact of quantum effects and thermal fluctuations on properties of small lithium clusters, Li8 and Li20, is investigated at low temperatures with ab initio path integrals. The static optimized structures, i.e., the minima of the potential energy surface, are characterized by packings of multicenter bonded tetrahedral building blocks featuring short and long Li–Li bonds. Quantum effects at 10 K are found to be induced by zero-point motion, whereas tunneling turns out to be irrelevant. The simulations uncover that these quantum effects destroy the distinction between short and long chemical bonds, while preserving the overall structural shape of the clusters.

Structure determination of lithium chloroacetate, lithium bromoacetate and lithium iodoacetate by powder diffraction

Most halogenoacetates of alkali salts readily undergo a thermally induced polymerization reaction to poly-(hydroxyacetic acid) in the solid state. The lithium salts represent a remarkable exception. The crystal structures of lithium chloroacetate, lithium bromoacetate and lithium iodoacetate were determined ab initio from synchrotron powder diffraction data. The three compounds are isostructural and differ considerably from the structures of sodium chloroacetate and silver chloroacetate, two compounds that undergo polymerization. Most likely, the strong polarizing effect of the small lithium cation is responsible for the unfavorable crystal structure in which each lithium cation is coordinated to four O atoms from four different halogenoacetate molecules. Lithium chloroacetate: a = 9.3882 (9), b = 4.8452 (4), c = 9.0119 (7) Å, beta = 94.330 (5) degrees; lithium bromoacetate: a = 9.7165 (11), b = 4.8610 (6), c = 9.0228 (11) Å, beta = 93.946 (5) degrees; lithium iodoacetate: a = 10.1812 (10), b = 4.8922 (8), c = 9.0468 (10) Å, beta = 93.251 (5) degrees, all crystallizing in space group P2(1)/c with Z = 4.

Resonating Valence Bond calculations on small anionic lithium clusters

We recast the Resonating Valence Bond theory, first introduced by Linus Pauling, in a nonorthogonal ab initio Valence Bond formalism and apply the method to study some properties of the anionic clusters \(\)\(\).We show how to choose appropriate structures and orbitals, and also how to use the so-called metallic orbitals. The problem of interpreting the role of a specific Valence Bond structure looking up its weight in the general wave function is elucidated. Information about the excited states of the systems is obtained. The theory can make good qualitative predictions on the electronic behaviour of the clusters by using a wave function that is a linear combination of a small set of structures. Pauling's theory is shown to be quite appropriate for describing anionic systems, specially the small ones, where the loosely bounded electron largely influences the properties of the systems. We verify the preference of some clusters for linear geometries.

Pellet charge exchange measurements of confined alphas in deuterium–tritium plasmas (invited) (abstract)

Alpha particle confinement is essential to achieving ignition in deuterium–tritium plasmas, and measuring the energy and spatial distributions of fusion alphas is one of the most challenging tasks in plasma diagnostics research. Confined trapped-alpha energy spectra and radial density profiles in the Tokamak Fusion Test Reactor (TFTR) have been obtained using the pellet charge exchange (PCX) diagnostic, which measures high energy (Eα=0.5–3.5 MeV), trapped alphas (|v∥/v|=0.048) at a single time slice (Δt∼1 ms) with a spatial resolution of Δr∼5 cm. PCX measures the energy spectrum of energetic helium neutrals resulting from charge exchange interactions of alphas incident on the ablation cloud surrounding small boron and lithium pellets injected radially into TFTR. The success of PCX has led to a number of important results on the behavior of alphas in TFTR. The measured alpha energy spectrum in the plasma core of sawtooth-free discharges is consistent with the alphas being well confined and slowing down classically. Outside the plasma core, the trapped alphas show the effects of stochastic diffusion due to the toroidal magnetic field ripple, with the PCX measured profiles consistent with the functional dependence of the stochastic ripple diffusion on the alpha energy and the q profile. Large sawtooth instabilities result in radial redistribution of the trapped alphas to well outside the q=1 radius and beyond the stochastic ripple loss boundary. Broadening of the radial profiles of trapped alphas is also observed in reversed and reduced shear discharges on TFTR, with potential implications for reactor designs based on optimized shear configurations. Finally, radial redistribution of trapped alpha particles in the presence of core localized Toroidal Alfv́en Eigenmode activity is also observed. Application of PCX measurements to future experiments, including the International Thermonuclear Experimental Reactor will also be discussed.

European helium cooled pebble bed blanket: Design of blanket: module to be tested in ITER

The helium-cooled pebble bed (HCPB) blanket for a fusion DEMO reactor is based on the use of separate small lithium orthosilicate and beryllium pebble beds placed between radial toroidal cooling plates. The cooling is provided by helium at 8 MPa. The tritium produced in the pebble beds is purged by the flow of helium at 0.1 MPa. The structural material is martensitic steel. It is foreseen, after extensive R&D, to test in ITER a blanket module based on the HCPB design which is one of the two European proposals for the ITER Test Blanket Programme. To facilitate the handling operations, the blanket test module (BTM) is bolted to a surrounding water cooled frame fixed to the ITER shield blanket back plate. For the design of the test module, 3D Monte Carlo neutronic calculations and thermo-hydraulic and stress analyses for the operation during the basic performance phase (BPP) and during the extended performance phase (EPP) of ITER have been performed. The behaviour of the test modules during LOCA, LOFA and electromagnetic transients has been investigated. Conceptual designs of the required ancillary loops have been performed.

An ab initio path integral Monte Carlo simulation method for molecules and clusters: Application to Li4 and Li5+

A novel method for simulating the statistical mechanics of molecular systems in which both nuclear and electronic degrees of freedom are treated quantum mechanically is presented. The scheme combines a path integral description of the nuclear variables with a first-principles adiabatic description of the electronic structure. The electronic problem is solved for the ground state within a density functional approach, with the electronic orbitals expanded in a localized (Gaussian) basis set. The discretized path integral is computed by a METROPOLIS Monte Carlo sampling technique on the normal modes of the isomorphic ring polymer. An effective short-time action correct to order τ4 is used. The validity and performance of the method are tested by studying two small lithium clusters, namely Li4 and Li5+. Structural and electronic properties computed within this fully quantum-mechanical scheme are presented and compared to those obtained within the classical nuclei approximation. Quantum delocalization effects turn out to be significant as shown by the fact that quantum simulation results at 50 K approximately correspond to those of classical simulations carried out at 150 K. The scaling factor depends, however, on the specific physical property, thus evidencing the different character of quantum and thermal correlations. Tunneling turns out to be irrelevant in the temperature range investigated (50–200 K).

Threshold photoionization behaviour of (Li $_2$ O)Li $_n$ clusters produced by a laser vaporization source

We report on the production of small and medium size lithium and lithium oxide clusters by a laser vaporization cluster source. The isotopomeric distribution of natural lithium allowed to identify LikO clusters as the most abundant components in the mass spectrum. Photoionization efficiency curves of LikO clusters with photon energies from 3.4 to 4.7 eV were measured for 8 ≤ k ≤ 27. Using linear extrapolation of the increase in photoionization efficiency with photon energy, ionization potentials were extracted. With the chemical bond of the O2- anion to two Li atoms, leaving n = k-2 valence electrons in the (Li2O)Lin clusters, clear shell closure effects are present at n = 8 and n = 20.

Grain growth kinetics of Li 3PO 4-doped calcium carbonate

Grain growth mechanisms of calcium carbonate doped with lithium phosphate were determined. With small lithium phosphate addition, an abnormal needle-like grain growth was observed. Addition of the dopant as solid solution in calcite follows the equation: Li 3PO 4 CaCO 3 →3(Li i +) + + V Ca 2+ 2− + (PO 4 3−) CO 3 2+ −. In slightly higher quantities (2 wt.%) above the solubility limit of Li 3PO 4, a second phase segregated at the grain boundaries. Whatever the thermal treatment (temperature, CO 2 partial pressure), the grain distribution was self-similar ( G( t)/ G ( t))=time independent) and followed a single log normal law. The grain growth kinetics can be described by the equation: d G /d t= k( G −1- G c −1). The grain growth was controlled by the mobility of the second phase.

Response to “Comment on ‘Density functional theory study of some structural and energetic properties of small lithium clusters’ ” [J. Chem. Phys. 107, 1032 (1997)

It is shown that whereas the spherical and spheroidal jellium models are inadequate to describe lithium clusters, only the ellipsoidal jellium model is adequate. The corresponding result, obtained by Yannouleas and Landman, was unpublished at the time of submission of our paper.

Comment on “Density functional theory study of some structural and energetic properties of small lithium clusters” [J. Chem. Phys. 105, 9933 (1996)

The Ionization Potentials of small LiN clusters are calculated with a Shell Correction Method. They are used to illustrate that, within the jellium approximation, deformed cluster shapes provide an adequate description of the observed systematic size dependence of the properties of simple metal clusters. Such deformation effects were overlooked in the analysis of Gardet et al.

Ab initiocalculations on small lithium clusters

We present a systematic study of the optimized geometries of several small closed-shell lithium clusters, as well as energy differences between isomers, using a variety of density functional and post-Hartree-Fock quantum chemical methods. Using different Gaussian basis sets we compare and contrast the results of the calculations for Li${}_{2}$, Li${}_{3}^{+}$, Li${}_{4}$, Li${}_{5}^{+}$, and Li${}_{6}$ including two and three isomers of the latter two clusters, respectively. On the basis of these results a few guidelines for economically but nevertheless reliably studying lithium clusters are proposed.