Lithium Concentration Profiles Research Articles

Lithium isotope fractionation by diffusion in minerals. Part 1: Pyroxenes

Several recent studies found large lithium isotopic fractionations correlated with concentration gradients in pyroxene minerals from lava flows and mantle nodules that were interpreted as indicating diffusion of lithium into the grains. Motivated by these findings experiments were undertaken in which powdered spodumene (LiAlSi2O6) or Li2SiO3 was used to diffuse lithium into Templeton augite or Dekalb diopside grains at 900°C and oxygen fugacity ranging from logfO2=−17 to logfO2=−12. The purpose of these experiments was to determine the diffusion coefficient of lithium in pyroxene minerals and to measure the isotopic fractionation of lithium in the diffusion boundary layer due to the relative mobility of 6Li compared to 7Li. The diffusion profiles of lithium that had not yet reached the center of Templeton augite grains were in most cases sharp steps propagating in from each boundary. In one case a more usual profile with smoothly decreasing lithium concentration with distance from the grain boundary was found. A model in which lithium occupies two different sites – one being fast diffusing interstitial lithium, the other much less mobile lithium in a metal site, reproduced both types of profiles. The step-like profiles arise in the model when interstitial lithium diffusing into the grain is strongly partitioned into abundant metal sites and thus does not penetrate further into the grain until all the metal sites at a given distance become filled. While the rate of propagation of the concentration step can be used to calculate an effective diffusivity for the penetration of lithium into the augite grains, the multiple speciation of lithium precludes making a separate precise determination of the diffusion coefficient of the interstitial lithium. Isotopic fractionations of 7Li/6Li of about 30‰ were found in the step-like diffusion boundary layers, which translate into a ratio of the isotope diffusion coefficients D7Li/D6Li=0.9592 (i.e., (6/7)β with β=0.27). The same value of β=0.27 was also able to fit the isotopic fractionation data from the experiment with the smoothly decreasing lithium concentration profile. The laboratory experiments confirmed that diffusion of lithium produces large kinetic isotopic fractionations and thus highlight the importance of isotopic measurements for discriminating when a particular instance of chemical zoning in minerals was the result of diffusion or some other process such crystal growth from an evolving melt. The experiments also showed that, contrary to conventional wisdom, isotopic gradients do not dissipate faster than gradients in the parent element, indeed the contrary is seen in several of the Templeton experiments where very large lithium isotopic fractionations persisted after the lithium concentration had become effectively homogenized. Published data of lithium isotopic fractionation of zoned augite grains from a Martian meteorite and in clinopyroxene grains from both lava flows on the Solomon Islands and from a San Carlos mantle xenolith were modeled in terms of lithium diffusion with an isotope fractionation parameter β between 0.25 and 0.30, which is very similar to that derived from the laboratory experiments.

A parameter study of intercalation of lithium into storage particles in a lithium-ion battery

The effect of stress on storage particles within a lithium ion battery, while acknowledged, is not fully understood. In this study we identify three non-dimensional parameters which govern the stress response within a spherical storage particle, and we carry out numerical simulations to characterize the stresses that are developed. The non-dimensional parameters are developed using system properties such as the diffusion coefficient, particle radius, lithium partial molar volume and Young’s modulus. Stress maps are generated for various values of these parameters for fixed rates of insertion, with boundary conditions applied to particles similar to those found in a battery. Stress and lithium concentration profiles for various values of these parameters show that the coupling between stress and concentration is magnified depending on the values of the parameters. The resulting maps can be used for different materials, depending on the value of the dimensionless parameters. Finally, the value of maximum stress generated is calculated for extraction of lithium from the particle and compared with those generated during insertion.

Parametrisation and estimation of surrogate critical surface concentration in lithium-ion batteries

In this paper a surrogate electrochemical lithium-ion battery model, presented and discussed in Di Domenico et al. (2008a) and Di Domenico et al. (2008b), is parametrised and validated through experimental data by a 10 cell 37 V 6.8 Ah Li-ion battery pack. Following past results (Zhang et al., 2000; Smith, 2010), the model is based on an approximate relationship between the electrode-averaged Butler-Volmer current and the solid-electrolyte interface concentration of a surrogate single particle for each cell electrode. Equally-spaced radially-discretised diffusion dynamics of the surrogate single particle for the positive electrode are then used to emulate the lithium concentration evolution in the cell. The surface concentration of the surrogate single particle, defined as surrogate Critical Surface Concentration (sCSC) is then used to predict the cell terminal voltage. The resulting model is as compact as an equivalent-circuit model but its underpinnings are lumped lithium-ion diffusion dynamics. A few parameters of the lumped lithium concentration dynamics are tuned using an iterative optimisation procedure with continuous and pulsed current profiles. The single particle lithium concentration profile and the surface concentration are then estimated using a 4th order Extended Kalman Filter (EKF) and the voltage predictions are compared with data.

Maximum Recommended Dosage of Lithium for Pregnant Women Based on a PBPK Model for Lithium Absorption.

Treatment of bipolar disorder with lithium therapy during pregnancy is a medical challenge. Bipolar disorder is more prevalent in women and its onset is often concurrent with peak reproductive age. Treatment typically involves administration of the element lithium, which has been classified as a class D drug (legal to use during pregnancy, but may cause birth defects) and is one of only thirty known teratogenic drugs. There is no clear recommendation in the literature on the maximum acceptable dosage regimen for pregnant, bipolar women. We recommend a maximum dosage regimen based on a physiologically based pharmacokinetic (PBPK) model. The model simulates the concentration of lithium in the organs and tissues of a pregnant woman and her fetus. First, we modeled time-dependent lithium concentration profiles resulting from lithium therapy known to have caused birth defects. Next, we identified maximum and average fetal lithium concentrations during treatment. Then, we developed a lithium therapy regimen to maximize the concentration of lithium in the mother's brain, while maintaining the fetal concentration low enough to reduce the risk of birth defects. This maximum dosage regimen suggested by the model was 400 mg lithium three times per day.

Determination of the lithium diffusion coefficient in irradiated boron carbide pellets

During neutron irradiation, 10B atoms in B 4C are destroyed, producing lithium and helium atoms according to the well-known 10B(n,α) 7Li reaction. The aim of this work is to measure the lithium diffusion coefficient of high density boron carbide material. The nuclear microprobe technique is used to determine lithium concentration profiles in irradiated B 4C pellets. The analysis of the measured lithium concentration profiles allows to calculate a lithium diffusion coefficient in this material.

Nuclear reaction analysis profiling as direct evidence for lithium ion mass transport in thin film ‘‘rocking-chair’’ structures

A nuclear reaction analysis technique using the p,γ reaction, 7Li(p,γ)8Be, occurring at approximately 440 keV, (half-width≊12 keV), has been utilized to determine the lithium concentration profiles in multilayer electrochromic window (‘‘smart window’’)/rechargeable battery cells when in their ‘‘colored’’/charged and ‘‘bleached’’/discharged states. The lithium profiles have been observed to shift according to the cells’ states, thereby providing direct experimental evidence for the so-called rocking-chair model for such structures.

Composition dependence of lithium diffusivity in lithium niobate at high temperature

An investigation was performed on the diffusivity of lithium in lithium niobate at 1100 °C in the crystallographic z direction over the composition range from 48.38 to 49.85 mol % Li2O. A vapor transport technique was applied to produce a lithium niobate crystal with a widely varying diffusion-limited lithium concentration profile. The profile was measured through spatially resolved measurement of the phase-match temperature for frequency doubling of a Nd:YAG laser. A Boltzmann–Matano analysis was applied to the profile to estimate diffusivity as a function of composition. The validity of the Boltzmann–Matano results was examined through numerical simulation, taking into account finite interfacial mass transport. A dramatic increase of lithium diffusivity with Li/Nb ratio was observed, ranging from roughly 3×10−9 cm2/s at the 48.38 mol % Li2O congruent composition to roughly 50×10−9 cm2/s at 49.85 mol % Li2O.

Methods for the determination of lithium and impurities in Pb17Li

Analytical methods for the determination of the main compounds and impurities in Pb17Li eutectic alloy which are used in our laboratory are summarized. Metallic impurities and the lithium content are analysed by means of atomic absorption spectrometry or optical emission spectrometry with inductive plasma excitation after decomposition of the samples in nitric acid. The determination of carbon is performed by combustion in oxygen and IR-absorption of CO2. Nitrogen is distilled as NH3 by means of the micro-Kjeldahl method and photometrically determined because of its small quantity. The most important non-metallic impurity is oxygen. The analysis for oxygen is performed using vacuum hot extraction. The samples have to be carefully protected against contamination by air and moisture.The estimation of oxygen contents resp. chemical activities is successfully performed using electrochemical meters. Thoria-yttria, zirconia-yttria or -calcia are suitable as solid electrolyte materials, indium-indium oxide serves as oxygen reference potential electrode. The advantage of the oxygen meters is that they detect the oxygen contents in solution in the liquid alloy. The meters can also be used to roughly measure the chemical activity of lithium in the liquid alloy. The temperature range to apply the meters is 350 to 500°C.Analytical techniques are also necessary to detect corrosion phenomena in suurface areas of materials. The glow discharge optical spectrometry is a method which determines elemental concentrations of up to 35 elements in relation to the distance from the surface. Measurements are performed up to 50 μm depth, from the adherent layer of Pb17Li into the material matrix. This technique has the capacity to measure quantitatively and sensitively lithium concentration profiles in the adherent layer and the corroded material.

Lithium diffusion in aluminum-lithium alloy 2090 clad with 7072

The loss of lithium during solution heat treatment of alloy 2090 clad with approximately 100 μm of 7072 was investigated. Lithium concentration profiles in the alloy were measured using a nuclear reaction analysis technique after samples had been subjected to various solution heat treatments. The results showed that the cladding-base metal interface provided no impediment to lithium diffusion and that the rate of lithium diffusion in the cladding was similar to its rate of diffusion in the base metal. A lithium-rich oxide was formed on the external surface, but the concentration profiles showed that the effective lithium concentration at the surface was near zero. Thus, lithium in the bulk experienced a maximum concentration gradient and diffused to the surface as rapidly as possible. Despite the absence of any lithium diffusion barrier in the cladding, the initial rate of lithium loss is much less than in bare material. The cladding provides effective protection from lithium loss, and the rate of loss in clad materials only approaches that of bare materials after approximately 4 hours.

Diffusion characteristics and waveguiding properties of proton-exchanged and annealed LiNbO3 channel waveguides

A discussion of the modeling of the proton exchange fabrication process is given, including a brief review of results of analytical measurements of concentration and concentration/index relation, as well as some presentation of the speculations made as to mechanisms of resulting index profiles. Discussion is then given to modeling of the exchange process itself via the ion exchange equations. The concentration profiles of protons and lithium in proton-exchanged LiNbO3 crystals measured by secondary ion mass spectroscopy are then presented. The proton concentration profiles are found to be nearly rectangular in shape. The diffusion characteristics of the ion exchange process are empirically modeled by solving the ion exchange equations with concentration dependent self-diffusion coefficients. Secondary ion mass spectroscopy (SIMS) measurements on annealed H+:LiNbO3 samples show proton and lithium concentration profiles to be Gaussian in nature. The proton and lithium concentration profiles of annealed H+:LiNbO3 samples are fit to the solutions of diffusion equations obtained from standard thermal diffusion theory. The fit has resulted in values of diffusion coefficient for protons during annealing (Dp=0.77 μm2/h). Index profiles are then calculated from these equations and are found to agree with the profiles reported elsewhere. Optical mode measurements on channel waveguides fabricated under various diffusion conditions and annealed for various times, are carried out. The mode-tailoring ability of the proton exchange process is demonstrated by fabricating low-loss single-mode channel guides (λ=0.83 μm) having channel widths as large as 6 and as small as 2.5 μm, simply by changing the diffusion conditions. Some anomalous results obtained in waveguides fabricated under extreme conditions are discussed.

Thermal oxidation behavior of an Al-Li-Cu-Mg-Zr alloy

The chemical composition of oxide films formed during thermal treatments of an Al-Li-Cu-Mg-Zr alloy has been studied by means of Auger electron spectroscopy and X-ray photoelectron spectroscopy. The oxide layers formed after oxidation of 2.5 minutes to 30 minutes at 530 °C in lab air have been characterized. In the early stages of oxidation the surface is composed of both the lithium rich oxides and magnesium rich oxides. However, after longer oxidation times the oxidation of lithium becomes predominant and the air/oxide interface is completely covered by lithium compounds. Oxidation products formed on the alloy surface have been studied by X-ray diffraction analysis. The following three phases, namely, Li2CO3, α-Li5AlO4, and γ-LiAlO2, were identified. During heat treatment in lab air at 530 °C and at atmospheric pressure the dominating reaction product is Li2CO3. Due to the selective oxidation of lithium a soft surface layer is developed. The width of the soft layer formed during solution heat treatments carried out in lab air and in salt bath environments has been determined by microhardness measurements. The lithium concentration profiles were calculated from a diffusion equation. The depletion of alloying elements from the near surface region during heat treatments has been investigated using energy dispersive X-ray analysis. The oxide morphology was examined using scanning electron microscopy and optical microscopy.

Application of nuclear reaction analysis to the investigation of lithium loss in the surface of Al-Li alloys

Lithium concentration profiles have been measured using a nuclear reaction analysis technique in an Al—Li alloy that had undergone solution treatment in different environments to determine the extent of lithium loss from the surface. A finely collimated beam of 2.5 MeV 3He ions, incident on the sample, induces the 7Li( 3He, p) 9Be reaction. The emitted protons are detected with a 200 mm 2 annular silicon detector capable of achieving a sensitivity for lithium of less than 0.01% by weight. Al—Li samples are mounted on a precision micrometer drive and translated through the beam to determine the lithium concentration profiles. The charged particle detection system is calibrated using Al—Li alloys having known bulk concentration of lithium. The lithium concentration profiles have been measured for an Al—Li alloy exposed to dry air, wet air and argon environments at 500°C for durations of 1, 4 and 16 h. Good agreement was obtained between these measurements and lithium diffusion calculations assuming a constant diffusivity, D = 2.5 × 10 −9cm 2/s. Knoop microhardness measurements made on the same Al—Li samples show a definite correlation with the measured lithium concentration profile.

Investigation of electrode glass membranes: Proposal of a dissociation mechanism for pH-glass electrodes

Leached surface layers of pH-glass electrode membranes formed in aqueous solutions were investigated by an ion-sputtering method. Reversible formation of steady-state lithium concentration profiles was observed on changing temperature, pH and hydrodynamic conditions of the leaching solution. While new steady-state profiles were reached within periods comparable with times necessary for generating the corresponding layers on fresh membranes, temperature decreases were followed by extremely slow profile changes depending on the temperature difference. The formation of reproducible, thermodynamically defined, pH-dependent Galvani tensions between solutions and pH-electrode membranes, despite the non-equilibrium and non-steady state of their leached surface layers, is explained by the dissociation of ⩾ SiOH groups at the interface between layer and solution which should be an equilibrium independent of layer structure and state.

Measurement of ion concentration profiles in surface layers of leached (“swollen”) glass electrode membranes by means of luminescence excited by ion sputtering

A new method is described of measuring concentration profiles of luminous ions in glass surface layers. The method is applied to so-called “swollen surface layers” of lithium ion containing electrode membrane glass after treatment (“swelling”) in solutions of different pH containing various alkali metal ions. Thickness (up to 300 Å) and lithium concentration profile of the layers are a function of pH and Li +-concentration of the solutions. The results are discussed in terms of ion-exchange equilibria. The layers are defined as “leached layers”.