Lithium Self-diffusion Coefficient Research Articles

Lithium Self-Diffusion in a Polymer Electrolyte for Solid-State Batteries: ToF-SIMS/ssNMR Correlative Characterization and Modeling Based on Lithium Isotopic Labeling.

Manufacturers aim to commercialize efficient and safe batteries by finding new strategies. Solid-state electrolytes can be seen as an opportunity to develop batteries with a high energy density. They allow the use of lithium foil as the anode, increasing the energy density. Also, they are composed of nonflammable materials making them safer than liquid electrolytes. However, to enhance the electrochemical performances of forthcoming solid-state lithium metal batteries, phenomena governing ionic conductivity have yet to be mastered in such devices. Lithium isotopic tracing was successfully used in previous works to further understand lithium ion transport mechanisms in batteries. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and 6/7Li high-resolution solid-state nuclear magnetic resonance (ssNMR) spectroscopy are two complementary techniques probing local and global scale, respectively. Both techniques can distinguish lithium isotopes. Here, four polymer membranes were elaborated with the same lithium concentration, but with various isotopic enrichments from 7.6 to 95.4% of 6Li. The selected material was a poly(ethylene oxide) (PEO) membrane containing lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) as lithium salt. They are widely studied in the lithium battery field. First, reliable ToF-SIMS and ssNMR methodologies were validated in light of the converging results. They led to accurate determination of lithium isotopic abundance of polymer membranes with a 1 or a 2% uncertainty, respectively. Then, the developed methodologies were applied to characterize lithium self-diffusion in a polymer membrane. Furthermore, numerical simulations based on a two-dimensional diffusion model compared with ToF-SIMS analyses allowed us to extract a lithium self-diffusion coefficient of 1.6 × 10-12 m2·s-1 at 60 °C, which complements other published values. The robust methodologies described in this work can be extended to various applications and materials. They stand as powerful strategies to better understand lithium ionic transport, especially in multiphase materials, for example, in hybrid solid-state electrolytes.

Dynamics of the extended and intermediate range order in model polymer electrolyte poly(ethylene oxide) and lithium bis(trifluoromethanesulfonyl)imide

The dynamics of lithium ions and polymer chains were investigated at the molecular scale in the model polymer electrolyte Poly (ethylene oxide) (PEO)/Lithium bis(trifluoromethanesulfonyl)imide as a function of temperature. This system is known to present an intermediate range order from the arrangement of neighboring chain segments as well as an extended range order of cylindrically arranged chains. The collective dynamics of the systems at lengthscales matching these structural features was measured using Neutron Spin Echo spectroscopy, gaining insights into their lifetime. Moreover, using isotope substitution techniques the dynamics of the lithium ions with respect to the other atoms was probed. The obtained results are compared with the conductivity and the lithium self-diffusion coefficient measured by NMR to gain experimental insight on the molecular processes triggering lithium transport.

Sulfurized Polyacrylonitrile (SPAN): Mechanical Properties and Reduction Mechanisms of Carbonate-Based Solvents on Its Surface

The lithium-sulfur (Li-S) system promises the most for the next generation of rechargeable batteries, as the Li-S battery offers a high theoretical energy density of 2567 Wh/kg and raw sulfur enjoys of widespread availability at low cost. The massive commercialization of this technology, however, relies heavily on tackling yet unsolved operational issues that dramatically diminish the practical energy density delivered by Li-S batteries, such as (i) low electric conductivity of sulfur and the sulfur reduction products, (ii) continuous loss of active sulfur due to shuttling of long-chain lithium polysulfides, and (iii) dendritic growth on the anode surface. An alternative strategy to solve these operational issues is the chemical sequestration of sulfur through sulfur-carbon bonding, which has shown improved electrochemical stability and longer cycling stability compared to the commonly used strategy of physical confinement of sulfur into a carbonaceous porous matrix. The sulfur polyacrylonitrile (SPAN) is now one of the most promising materials for chemical sequestration of sulfur. Experiments and theoretical calculations have shown that this material avoids the formation of long-chain lithium polysulfides and allows the introduction of carbonate-based solvents into the electrolyte, which opens up the possibility of using the same electrolyte manufacturing technology of Li-ion batteries for Li-S batteries. Even though the advantages that SPAN materials bring for the development of the Li-S battery technology, there is still a lack of understanding on how to increase the sulfur loading, fundamental to guarantee high energy density, and also on why the SPAN performs better with carbonate-based electrolytes compared to the ether-based electrolytes traditionally used in Li-S batteries. In this work, we aimed at characterizing the mechanical properties of the SPAN and the chemical reactions at the electrolyte-SPAN interface. Reactive molecular dynamics (ReaxFF) calculations allowed evaluating the stress-strain behavior of the SPAN and the lithium self-diffusion coefficient as a function of sulfur content and lithiation stage, whereas Ab initio molecular dynamics (AIMD) calculations aimed at identifying the reduction mechanisms of carbonate-based solvents such as ethylene carbonate (EC) and fluoroethylene carbonate (FEC) on SPAN surfaces various degrees of lithiation. We elucidated the impact that sulfur loading has on the SPAN structural stability and the accessibility of lithium into those regions where sulfur agglomerates in the SPAN structure, allowing us to find out a trade-off between sulfur loading, structural stability, and electrochemical activity. Regarding the solvent/SPAN interface dynamics, we elucidate the EC/FEC decomposition mechanisms on the SPAN surface and its dependence on the lithiation degree. We believe that our results will contribute to the development of SPAN-based cathodes with higher areal-loading and a high-quality solid electrolyte interphase (SEI) protecting the electrode.

Slice-Selective NMR Diffusion Measurements - a Tool for the Characterization of Ion Transport Properties in Lithium Ion Battery Electrolytes

The main impediments to the wide-spread acceptance of electric drive vehicles are the cost, energy storage capacity, and durability of Li-ion batteries. The first issue is best addressed within the context of materials and batteries manufacturing, the second by research on the synthesis and characterization of new materials. Successfully tacking of the third issue requires an improved understanding of battery degradation mechanisms and the development of suitable mitigation measures. In situ experimental techniques which can accurately detect and monitor performance degradation mechanisms at the nanoscale, including the identities of short-lived chemical species, or changes in materials properties as functions of temperature, position or time are emerging only gradually, due to their associated difficulties and complex challenges. We show that the combination of in situ one-dimensional imaging and slice-selective NMR diffusion measurements (Fig. 1) is a tool for spatially and temporally resolving the lithium self-diffusion coefficient in a liquid electrolyte during the application of a dc current (Fig. 2). A solution of 1M LiTFSI in propylene carbonate was used for our method development work.

Concentration effects on aqueous lithium chloride solutions. Molecular dynamics simulations and x-ray scattering studies

Molecular dynamics simulations have been performed on aqueous LiCl solutions over a wide range of salt concentrations, using a flexible SPC/E water model. The resulting molecular dynamics structure factors agree remarkably with recently published x-ray ones. The diffusion coefficients of both ions and water decrease with increasing salt concentration. The self-diffusion coefficients of lithium and chloride are nearly equal at higher salt concentration, showing that large clusters of ions move as an entity. The deduced reorientational correlation time for the dipole moment speeds up as the salt concentration increases, indicating the presence of an angular jump model. The dielectric constant decreases with increasing salt concentration.

Self-Diffusion of Lithium in LiAlSi2O6 Glasses Studied Using Mass Spectrometry

In order to improve our understanding of the transport mechanisms of lithium in glasses, we have performed diffusion and ionic conductivity studies on spodumene composition (LiAlSi(2)O(6)) glasses. In diffusion couple experiments pairs of chemically identical glasses with different lithium isotopy (natural Li vs pure (7)Li) were processed at temperatures between 482 and 732 K. Profiles of lithium isotopes were measured after the diffusion runs innovatively applying femtosecond UV laser ablation combined with inductively coupled plasma mass spectrometry (LA ICP-MS). Self-diffusion coefficients of lithium in the glasses were determined by fitting the isotope profiles. During some of the diffusion experiments the electrical conductivity of the samples was intermittently measured by impedance spectrometry. Combining ionic conductivity and self-diffusivity yields a temperature-independent correlation factor of ~0.50, indicating that motions of Li ions are strongly correlated in this type of glasses. Lithium self-diffusivity in LiAlSi(2)O(6) glass was found to be very similar to that in lithium silicate glasses although Raman spectroscopy demonstrates structural differences between these glasses; that is, the aluminosilicate is completely polymerized while the lithium silicate glasses contain large fractions of nonbridging oxygen.

Self-diffusion coefficient study of liquid lithium

Little liquid lithium experimental self-diffusion coefficient were reported in the literature because of higher risk of radiation measurement method of diffusion coefficient. In the paper, the EAM potential is applied to calculate self-diffusion coefficient of liquid lithium with emphasis on a wide range of temperature, pressure, magnetic field, and gravity acceleration. The results show that the liquid lithium self-diffusion coefficient increases with temperature increasing and decreases with pressure increasing. Calculated self-diffusion coefficient is in good agreement with Murday’s experiment results in atmosphere. We get the Arrhenius equation according to the simulation results. The increasing of pressure enlarges the liquid lithium activation energy and lowers the movement of atom in liquid lithium.

Self-diffusion of lithium, hydrogen, and oxygen ions in crystalline lithium hydroxide

The self-diffusion coefficients of ions of the three chemical elements forming lithium hydroxide have been determined by the crystal-crystal and crystal-gas isotope exchange method in the temperature range 500–720 K. Crystal samples with different isotope compositions have been grown by the Bridgman method from melts. The melting temperature is 743 ± 2 K. Original methods have been developed for high-precision measurements of the isotope ratios of all three elements, i.e., lithium (6Li/7Li), hydrogen (H/D), and oxygen (16O/18O), and their changes after diffusion annealings with the use of the same sample. The self-diffusion coefficients of lithium and hydrogen ions differ but by a factor of no more than 3–5; however, their values exceed those for oxygen by several orders of magnitude. In particular, at 670 K, they are equal to 6.0 × 10−9, 3.2 × 10−9, and 2.0 × 10−12 cm2 s−1 for hydrogen, lithium, and oxygen, respectively. In the range 680–720 K, the self-diffusion coefficients of hydrogen and lithium increase sharply with increasing temperature to approximately 10−6 cm2 s−1. A probable mechanism of migration of protons and lithium ions in LiOH and the role played in this process by the oxygen ions with a lower mobility have been discussed.

Transport properties of ionic liquid electrolytes with organic diluents

Ionic liquids (ILs) form a novel class of electrolytes with unique properties that make them attractive candidates for electrochemical devices. In the present study a range of electrolytes were prepared based on the IL N-methyl-N-propylpyrrolidinium bis(trifluoromethylsulfonyl) amide ([C(3)mpyr][NTf(2)]) and LiNTf(2) salt. The traditional organic solvent diluents vinylene carbonate (VC), ethylene carbonate (EC), tetrahydrofuran (THF) and toluene were used as additives at two concentrations, 10 and 20 mol%, leading to a ratio of about 0.6 and 1.3 diluent molecules to lithium ions, respectively. Most promisingly, the lithium ions see the greatest effect in the presence of all the diluents, except toluene, producing a lithium self-diffusion coefficient of almost a factor of 2.5 times greater for THF at 20 mol%. Raman spectroscopy subtly indicates that THF may be effectively breaking up a small portion of the lithium ion-anion interaction. While comparing the measured molar conductivity to that calculated from the self-diffusion coefficients of the constituents indicates that the diluents cause an increase in the overall ion clustering. This study importantly highlights that selective ion transport enhancement is achievable in these materials.

Molecular dynamics simulations of kinetic isotope fractionation during the diffusion of ionic species in liquid water

Interpretation of isotope ratios, a powerful tool in geochemical investigations of fluid-rock systems, requires an understanding of all relevant processes that fractionate isotopes. One such process, diffusion in liquid water, has remained problematic despite its potential significance as a major cause of kinetic isotope fractionation. Recent laboratory experiments published by [Richter, F. M., Mendybaev, R. A., Christensen, J. N., Hutcheon, I. D., Williams, R. W., Sturchio, N. C., and Beloso Jr., A. D. (2006) Kinetic isotopic fractionation during diffusion of ionic species in water. Geochim. Cosmochim. Acta 70, 277–289.] have shown clearly for the first time that lithium and chloride isotopes are fractionated by diffusion in liquid water, whereas magnesium isotopes are not. In the present paper, we present the results of molecular dynamics simulations of lithium, chloride, and magnesium diffusion in liquid water that were designed to provide molecular-scale insight into the experimental findings of Richter et al. (2006). Our results indicate that the self-diffusion coefficients of lithium, chloride, and magnesium isotopes follow an inverse power-law dependence on ion mass ( D i ∝ m i - β , where D i is the self-diffusion coefficient of a solute with isotopic mass m i ). The power-law exponents ( β) deduced for lithium, chloride, and magnesium from the diffusivity data of Richter et al. (2006) are consistent with the mass dependencies found in our simulations. Further analysis of our simulation results showed that the experimental β-values are inversely related to the residence times of water molecules in the first solvation shells of the diffusing ions, as expected from mode-coupling and renormalized kinetic theories.

Investigation of ionic conduction and mechanical properties of PMMA–PVdF blend-based polymer electrolytes

Polymeric gel electrolytes, based on a blend of poly(methylmethacrylate)/poly(vinylidene fluoride) (PMMA/PVdF), ethylene carbonate/propylene carbonate (EC/PC) as plasticizer and lithium perchlorate as electrolyte, have been studied as a function of the different polymeric ratios to obtain the best compromise between ionic conduction and mechanical properties of the systems involved. Ionic conductivity and the lithium self-diffusion coefficient were measured by the PFG–NMR method, which revealed a maximum of lithium mobility for the composition PMMA 60%–PVdF 40%. The Raman spectroscopic study revealed a change of the interaction between that of the lithium cations and the plasticizer molecules for different PMMA / PVdF ratios. Oscillatory rheological tests have shown better mechanical properties for the intermediate compositions of the blend.

The role of structural and electronic alterations on the lithium diffusion in LixCo0.5Ni0.5O2

The mechanisms for lithium diffusion in LixCo0.5Ni0.5O2 were investigated using the galvanostatic intermittent titration technique (GITT). Membrane electrodes prepared with poly(vinylidene fluoride) and carbon black were employed in this study. The measured Brunauer–Emmett–Teller (BET) area of the LixCo0.5Ni0.5O2 powder was combined with the GITT data to obtain the lithium chemical diffusion coefficient (ĎLi+), the lithium self-diffusion coefficient (DLi+) and the thermodynamic factor (Φ) as a function of Li concentration (x). All three parameters vary non-monotonically with x. A minimum in ĎLi+ and DLi+ at x=0.5, along with structural changes, suggests the formation of a lithium superlattice at that concentration. The behavior of ĎLi+ is complex but for x<0.34 it eventually undergoes a continuous decrease due to the metallic character of LixCo0.5Ni0.5O2. We attribute the limitation of the specific reversible capacity of LixCo0.5Ni0.5O2 to this decrease in ĎLi+ and to elevated electrode voltages. Li transport in LixCo0.5Ni0.5O2 is analyzed taking the variations in the cell parameters and the oxidation states of the Ni, Co and O ions into account.

The role of structural and electronic alterations on the lithium diffusion in Li xCo 0.5Ni 0.5O 2

The mechanisms for lithium diffusion in Li x Co 0.5Ni 0.5O 2 were investigated using the galvanostatic intermittent titration technique (GITT). Membrane electrodes prepared with poly(vinylidene fluoride) and carbon black were employed in this study. The measured Brunauer–Emmett–Teller (BET) area of the Li x Co 0.5Ni 0.5O 2 powder was combined with the GITT data to obtain the lithium chemical diffusion coefficient ( D ̌ Li + ), the lithium self-diffusion coefficient ( D Li + ) and the thermodynamic factor ( Φ) as a function of Li concentration ( x). All three parameters vary non-monotonically with x. A minimum in D ̌ Li + and D Li + at x=0.5, along with structural changes, suggests the formation of a lithium superlattice at that concentration. The behavior of D ̌ Li + is complex but for x<0.34 it eventually undergoes a continuous decrease due to the metallic character of Li x Co 0.5Ni 0.5O 2. We attribute the limitation of the specific reversible capacity of Li x Co 0.5Ni 0.5O 2 to this decrease in D ̌ Li + and to elevated electrode voltages. Li transport in Li x Co 0.5Ni 0.5O 2 is analyzed taking the variations in the cell parameters and the oxidation states of the Ni, Co and O ions into account.

Investigation of the solution condition of lithium electrolyte solutions with LiCF3SO3 salt

Solution condition of the lithium electrolyte of LiCF3SO3 salt dissolved in propylene carbonate (PC), dimethoxyethane (DME) and tetrahydrofuran (THF) were investigated based on the measurements of the self-diffusion coefficients of lithium (DLi) and anion (DF) species using the pulsed-field gradient (PFG) NMR, viscosity and conductivity. DLi and DF decreased with the increase in the solution concentration for these electrolytes. This result reflects the change in the dissociation degree of the salt and the viscosity depending on the solution concentration. In the case of PC solution (the dielectric constant (∈) of PC: ∼65), measured DLi and DF were separated each other with the decrease in the concentration because the dissociation of the salt was promoted to increase the content of dissociated ions. With an increase in the concentration, the dissociation would be restricted and DLi and DF approximated each other, which means that the associated ion pairs are dominant in the solution. The effective ionic radius (reff) of cation species of PC solution estimated from the Stokes-Einstein relation using the diffusion coefficient and the viscosity results was four times greater than that of the naked lithium ion and independent of the dissociation degree. On the other hand, the reff of anion species changed depending on the dissociation degree. This suggests that the dissociated lithium ions are solvated by the PC solvent in the solution. DME and THF solutions did not show the solvation effect from the result of the change in reff with the concentration. This suggests that the dissociation degree of the dissolved salt was low due to the low ∈ of their solvents (∈ ∼ 7.2) and the ion pairs would dominant in the solutions independent of the solution concentration.

Self-diffusion coefficients of lithium, anion, polymer, and solvent in polymer gel electrolytes measured using 7Li, 19F, and 1H pulsed-gradient spin-echo NMR

Four series of solution and corresponding polymer gel electrolyte systems were studied. The systems were composed of a solvent (γ-butyrolactone (GBL) or propylene carbonate (PC)), (three different concentrations of) a lithium salt (LiBF 4 or lithium bis(trifluromethanesulfonyl)-imide (LiTFSI, LiN(SO 2CF 3) 2)), and poly(ethylene glycol diacrylate) of molecular weight 4000 (PEO), which was cross-linked to form the polymer gels. The self-diffusion coefficients of the lithium, the anions, the solvents and the polymer were obtained independently using 7Li, 19F and 1H pulsed-gradient spin-echo NMR measurements. From the individual diffusion coefficients of each component of the GBL–LiBF 4, GBL–LiTFSI, PC–LiBF 4, and PC–LiTFSI solutions and the corresponding polymer gel electrolytes, the solvation and the solvent-dependent behaviour of the lithium and the anions are clearly shown. Especially in the gels, the lithium binding with the PEO matrix were found to be quite different depending on whether the solvent was PC or GBL.

Ionic conductivity, DSC and self diffusion coefficients of lithium, anion, polymer, and solvent of polymer gel electrolytes: the structure of the gels and the diffusion mechanism of the ions

The polymer gel electrolytes studied in this paper are composed of two kinds of organic solvents (γ-butyrolactone (GBL) or propylene carbonate (PC)), two kinds of lithium salts (LiBF 4 or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, LiN(SO 2CF 3) 2)) and chemically cross-linked poly(ethyleneoxide) (PEO). The ionic conductivity and the thermal properties were measured by the AC impedance method and differential scanning calorimetry (DSC), respectively. The individual self diffusion coefficients ( D) of the electrolyte components measured by the pulsed-gradient spin-echo (PGSE)-NMR method were compared with the ionic conductivities to clarify the ionic conduction mechanisms, the ion compositions and the degree of dissociation. The results suggest that although the degrees of ion dissociation in the gel electrolytes are larger than in the liquid electrolytes, the ionic conductivities of the gels are lower than that of the liquids due to the slower diffusion of the lithium ion. From diffusion behaviours observed at various salt concentrations in the gels (especially in the PC-based gels), it was found that the lithium ions are trapped in the polymer matrix.

Kinetics of electrochemical insertion of lithium into WO

A kinetic study of the electrochemical insertion of lithium into the original form of WO 3, formed by the heat-treatment of H 2WO 4 at 448 K, were carried out using an ac impedance method. The chemical diffusion coefficients, D̃, of lithium in the oxide were measured as functions of the lithium composition and temperature by using several kinds of electrolytes. The obtained values of D̃, based on a geometric surface area, depended strongly on the lithium composition and the kind of electrolytes. The D̃ values, obtained using 1M LiClO 4 and 1M LiAsF 6 solutions of propylene carbonate, were of the order of 10 −11 cm/s at 298 K for 0.2< x<1.0 in Li x WO 3, corresponding to a lithium self-diffusion coefficient of the order of 10 −12 cm 2/s, while using the 1M LiBF 4 and 1 M LiPF 6 solutions considerably lower values of D̃, 10 −13−10 −12 cm 2/s, were obtained for 0.2< x<1.0. The activation energy for the diffusion of lithium in WO 3 obtained using the former electrolyte (20–40 kJ/mol) is typical of diffusion in intercalation materials, whereas that obtained using 1M LiBF 4 solution (∼60 kJ/mol) corresponds to the kinetics controlled by the surface layer.

Kinetic and structural characteristics of 3R-niobium disulfide as a positive material for secondary lithium batteries

The kinetic and thermodynamic studies of the intercalation process of lithium ions in the layered structure of niobium disulfide with a 3R-type-modification were made. The standard free energy of lithium intercalation into the van der Waals gaps, Δ G 0 I, was −218 kJ mol −1 at 298 K in the range of x = 0–1 in Li xNbS 2. Applying the thermodynamic model by Nagelberg and Worrell [Nagelberg and Worrell, J. Solid St. Chem. 38, 321 (1981)] the interaction energy between the intercalated lithium ions was estimated as a model parameter. The chemical diffusion coefficients, D̃, of lithium in the disulfide were measured as functions of the lithium composition and temperature by using several kinds of electrolytes and an ac impedance method. The obtained values of D̃, based on a geometrical surface area, were dependent on the lithium composition and the kind of electrolytes. The values of D̃ obtained in 1M LiClO 4 and 1 M LiAsF 6 solutions of propylene carbonate were found to be of the order of 10 −8 cm 2s −1 at 298 K for 0.2 < x <0.6 in Li x NbS 2, corresponding to a lithium self-diffusion coefficient of 10 −9 cm 2s −2 order, while in the 1 M LiBF 4 solution a considerably lower values of D̃, 10 −10-10 −11 cm 2s −1, were obtained for 0.1 < x<0.5. The activation energies for the diffusion of lithium in the range of 20–30 kJ mol −1 in the LiClO 4 and LiAsF 6 solutions, and in the range of 80–90 kJ mol −1 in the LiBF 4 solution; the values in the former electrolytes are typical of diffusion in layered insertion materials, whereas in the latter electrolyte the kinetics may be controlled by the surface layer.

Lithium ion diffusion in the defect thiospinel Li xCu 0.07Ti 2S 4 (0.1 ⩽ x ⩽ 1.85)

The room-temperature chemical diffusion coefficient ( D) of lithium in the lithiated defect thiospinel Li x Cu 0.07Ti 2 S 4 (0.1 ⩽ x ⩽ 1.85) was measured by galvanostatic pulse and ac impedance methods. The galvanostatic pulse experiment gave D = 1 × 10 −9 cm 2s −1 ( x = 1.0) at 293 K. This corresponds to a lithium self-diffusion coefficient D Li = 2 × 10 −10cm 2s −1 and to a bulk lithium-ion conductivity α Li = 6 × 10 −6 ω −1cm −1. The ac impedance experiments gave similar values of D over most of the lithium composition range, but indicated that D is an order of magnitude lower at the extreme compositions x = 0.1 and x = 1.85. The lithium-ion chemical diffusion coefficient in Li x Cu 0.07Ti 2S 4 is thus clearly lower than that in the corresponding layered insertion compounds Li x TiS 2 ( D≈1 × 10 −8cm 2s −1; this may be due to the residual copper present in Li x Cu 0.07Ti 2S 4.

Vacancy-antistructure defect interaction diffusion in β-LiAl and β-LiIn

The lithium mass transport mechanisms of the NaTl-type intermetallic compounds β-LiAl and β-LiIn were studied by using the pulsed-field-gradient (PFG) nuclear magnetic resonance (NMR) spin-echo technique over a temperature range of 297–485 K. The lithium self-diffusion coefficients in β-LiAl alloys were found to follow Arrhenius behavior. The lithium diffusion coefficient and the associated diffusion constant D 0 (Li) and activation energy 〈E〉 decrease with increasing lithium content. The results can be interpreted if two types of vacancy point defects are considered: vacancies associated with immobile antistructure defects and vacancies which are otherwise free. A vacancy-diffusion mechanism based on two mean effective jump times, τ A and τ B τ B / τ A = 9.0), for these two types of vacancies yields a quantitative description of the dependence of the lithium diffusion rate on defect concentrations under a V Li − Li Al attractive interaction at a nearest neighbor distance. Very high values of lithium diffusivities (approximately 10 −6 cm 2 s −1 at room temperature) which increase with decreasing lithium content were observed in β-LiIn alloys. The lithium self-diffusion coefficient obeys the Arrhenius relation over the temperature range 300–400 K. The diffusion constant D 0 (Li) and activation energy 〈E〉 determined from the Arrhenius relation decrease with increasing lithium content. The results suggest that there is a repulsive interaction between the vacancy V Li and the antistructure atom Li In. Theoretical analyses based on a three-effective-jump-times diffusion model indicate that this V Li − Li In repulsive interaction is so strong that it extends well into the second nearest-neighbor distance.