Li-Mg Alloys Research Articles

Role of Short-Range Order on Diffusion Coefficients in the Li-Mg Alloy.

Li-Mg alloys are important because of their beneficial role in fostering uniform plating and stripping of lithium in all-solid-state batteries. The alloy forms a solid solution on the BCC crystal structure when the lithium content is greater than x ≈ 0.3. The activation barriers of lithium and magnesium exchanges with a vacancy, crucial for substitutional diffusion, are predicted to be exceptionally low and almost identical, with negligible dependence on the alloy composition. The equilibrium vacancy concentration at room temperature is predicted to be very low, and it also remains almost constant with no dependence on Mg content in the alloy (for ). Nevertheless, both experiments and kinetic Monte Carlo simulations indicate that the tracer diffusion coefficients decrease by almost an order of magnitude with the addition of Mg to the alloy. In this contribution, the crucial role that chemical short-range order plays in affecting the diffusion coefficients is studied. Chemical short-range order is found to increase the effective activation barrier for lithium and magnesium diffusion by making successive atomic hops with vacancies correlated.

On the Relative Importance of Li Bulk Diffusivity and Interface Morphology in Determining the Stripped Capacity of Metallic Anodes in Solid-State Batteries.

Lithium metal self-diffusion is too slow to sustain large current densities at the interface with a solid electrolyte, and the resulting formation of voids on stripping is a major limiting factor for the power density of solid-state cells. The enhanced morphological stability of some lithium alloy electrodes has prompted questions on the role of lithium diffusivity in these materials. Here, the lithium diffusivity in Li-Mg alloys is investigated by an isotope tracer method, revealing that the presence of magnesium slows down the diffusion of lithium. For large stripping currents the delithiation process is diffusion-limited, hence a lithium metal electrode yields a larger capacity than a Li-Mg electrode. However, at lower currents we explain the apparent contradiction that more lithium can be extracted from Li-Mg electrodes by showing that the alloy can maintain a more geometrically stable diffusion path to the solid electrolyte surface so that the effective lithium diffusivity is improved.

3D artificial electron and ion conductive pathway enabled by MgH2 nanoparticles supported on g-C3N4 towards dendrite-free Li metal anode

Li metal anode is considered as one of the most promising candidates for next-generation batteries due to its high energy density. The undesired growth of Li dendrites and infinite volume change, however, hinders its practical application. Herein, a 3D structured Li metal anode featured with uniform electron and Li ion conductive pathway is fabricated through the favorable reaction between MgH2 that are uniformly distributed on g-C3N4 and molten Li. The thus-formed lithiophilic LiMg alloys under the structural support of lithiophilc g-C3N4 could synergistically lower the nucleation barrier of Li plating and hence promote the uniform Li deposition process. Simultaneously, the high Li ion conductivity of thus-formed both LiH and Li3N resulting from the reaction between molten Li and MgH2 and g-C3N4, respectively, facilitates fast Li ion transportation kinetics along their surfaces towards favorable Li deposition on the surface of g-C3N4. Consequently, the thus-fabricated Li metal anode with a high specific capacity of 3511 mA h g − 1 delivers a long cycling life of over 500 h at 3 mA cm−2 under 3 mA h cm−2. Impressively, upon coupling this anode with commercial LFP cathode, the thus-assembled full cells deliver a specific capacity of 145 mA h g − 1 after 450 cycles at 1 C.

Identifying the positive role of lithium hydride in stabilizing Li metal anodes.

Lithium hydride has been widely identified as the major component of the solid-electrolyte interphase of Li metal batteries (LMBs), but is often regarded as being detrimental to the stabilization of LMBs. Here, we identify the positive and important role of LiH in promoting fast diffusion of Li ions by building a unique three-dimensional (3D) Li metal anode composed of LiMg alloys uniformly confined into graphene-supported LiH nanoparticles. The built-in electric field at the interface between LiH with high Li ion conductivity and LiMg alloys effectively boosts Li diffusion kinetics toward favorable Li plating into lithiophilic LiMg alloys through the surface of LiH. Therefore, the diffusion coefficient of Li ions of the thus-formed 3D structured Li metal anode is 10 times higher than the identical anode without the presence of LiH, and it exhibits a long cycle life of over 1200 hours at 3 mA cm−2 under 5 mA hour cm−2.

Dendrite‐Free Li‐Metal Anode Enabled by Dendritic Structure

AbstractThe practical application of Li‐metal anode in high‐energy rechargeable Li batteries is still hindered by the uncontrollable formation of Li dendrites. Here, a facile way is reported to stabilize Li‐metal anode by building dendrite‐like Li3Mg7 alloys enriched with Li‐containing polymers as the physical protecting layer and LiH as the Li‐ion conductor. This unique dendritic structure effectively reduces local current density and accommodates volume change during the repeated Li plating/stripping process. More importantly, lithiophilic Li3Mg7 alloys not only guide the uniform Li deposition down into the below Li metal upon Li deposition, but also thermodynamically promote the extraction of Li during the reverse Li stripping process, which suppresses the parasitic reactions occurring on the surface of Li metal and hence inhibits the formation of Li dendrites. Moreover, the facile diffusion of Mg from Li3Mg7 alloys toward Li metal below is thermodynamically permitted, which leads to a uniform distribution of LiMg alloys inside the whole electrode and thus benefits long‐term deep cycling stability. As a result, the protected Li‐metal anode delivers stable and dendrite‐free cycling performance at 10 mA h cm−2 for over 900 h. When coupling this anode with LiFePO4 and S cathodes, the thus‐assembled full cells exhibit superior cycling stability.

Computational study of the magnetic and electronic properties of the LiMgN(Vc1-xZx) and LiMg(N1-xZx) alloys where Z is B, C or S

In this investigation, we performed our calculations within the Korringa-Kohn-Rostoker (KKR) scheme and Coherent Potential Approximation (CPA) as implemented in the MACHIKANEYAMA2002v08 package based on density-functional-theory to compute the electrical and magnetic properties of LiMg(N1-xZx) and LiMgN(Vc1-xZx). Z ≡ “B, C and S” where “Vc” stands for vacancy sites. The goal is to examine the ferromagnetic characteristic at low concentration amount: x = 0.02, 0.03, 0.04, 0.05. The obtained band gap is of 2.76eV. The density of states (DOS) have been analyzed, the LiMg(N1-xBx) shown the ferromagnetic (FM) stability, where there is no evidence of this behavior in LiMg(N1-xSx), since the TDOS is symmetric and the total spin moment is null. For the LiMgN(Vc1-xSx), the ferromagnetic behavior is induced by the S element incorporated in vacancy sites, which exhibits the p-type conductivity. the main contribution in the total magnetic moment is from the sulfur, it is of MS = 0.40802 μB. The outcomes of this work made these systems as promising candidates in magnetoelectronic application thanks to their ferromagnetism.

The Nature of Electrochemical Delithiation of Li-Mg Alloy Electrodes: Neutron Computed Tomography and Analytical Modeling of Li Diffusion and Delithiation Phenomenon

Li-Mg alloys are promising as positive electrodes (anodes) for Li-ion batteries due to the high Li storage capacity and the relatively lower volume change during the lithiation/delithiation process. They also present a unique opportunity to image the Li distribution through the electrode thickness at various delithiation states. In this work, spatial distributions of Li in electrochemically delithiated Li-Mg alloy electrodes have been quantitatively determined using neutron tomography. Specifically, the Li concentration profiles along thickness direction are determined. A rigorous analytical model to quantify the diffusion-controlled delithiation, accompanied by phase transition and boundary movement, has also been developed to explain the delithiation mechanism. The analytical modeling scheme successfully predicted the Li concentration profiles which agreed well with the experimental data. It is demonstrated that during discharge Li is removed by diffusion through the solid solution Li-Mg phases and this proceeds with β→α phase transition and the associated phase boundary movement through the thickness of the electrode. This is also accompanied by electrode thinning due to the change in molar volume during delithiation. Following the approaches developed here, one can develop a rigorous and quantitative understanding of electrochemical delithiation in electrodes of electrochemical cells, similar to that in the present Li-Mg electrodes.

Improvement of Cycle Life of Lithium Air Batteries Using Ag and Mg Alloyed Li Anode

Lithium-air batteries have attracted great interest due to great theoretical specific energy of Li-air excluding oxygen is 11.5 kWhkg−1, the value of which is comparable with that of gasoline/air device. This high energy density battery has the potential to be the power source for the advanced electric vehicles. However, there are a lot of challenges, one of which is low cycleability of lithium-air batteries because of formation dendrites on lithium anode and most significantly very high corrosion of lithium metal when room temperature ionic liquids (RTILs) are used. In this study, it was aimed to increase corrosion resistance therefore, cycleability of anode materials in Li-air battery cells by using mechanical alloying with silver and magnesium powders. The effect of the silver and magnesium on the electrochemical behavior of lithium anode for lithium-air batteries were investigated. Fine granules of Li metal and silver or magnesium were used as starting materials. At the first step the production of the Li-Ag and Li-Mg alloys was optimized in the mechanical alloying process. Subsequently, Li-Ag or Li-Mg powder alloys were synthesized as anode materials. The high energy ball milling was performed under argon atmosphere at room temperature. The alloys produced by mechanical alloying were cold pressed to produce dense lithium alloys. The physical characterization of the produced anodes was evaluated by X-ray diffraction (XRD) and scanning electron microscopy(SEM). Electrochemical analysis of the lithium and lithium alloys were carried out using a Swagelok-type cell with 1 M LiPF6 in TEGDME as electrolyte and GDL (gas diffusion layer) as cathode and prepared Li-Ag and Li-Mg powders as working anode. The electrochemical impedance spectroscopy (EIS) measurement of the lithium and alloys have been conducted to investigate the difference in the resistance of the cell before and after electrochemical cyclic test.

The Effect of H2 Partial Pressure on the Reaction Progression and Reversibility of Lithium-Containing Multicomponent Destabilized Hydrogen Storage Systems

It is known that the reaction path for the decomposition of LiBH(4):MgH(2) systems is dependent on whether decomposition is performed under vacuum or under a hydrogen pressure (typically 1-5 bar). However, the sensitivity of this multicomponent hydride system to partial pressures of H(2) has not been investigated previously. A combination of in situ powder neutron and X-ray diffraction (deuterides were used for the neutron experiments) have shed light on the effect of low partial pressures of hydrogen on the decomposition of these materials. Different partial pressures have been achieved through the use of different vacuum systems. It was found that all the samples decomposed to form Li-Mg alloys regardless of the vacuum system used or sample stoichiometry of the multicomponent system. However, upon cooling the reaction products, the alloys showed phase instability in all but the highest efficiency pumps (i.e., lowest base pressures), with the alloys reacting to form LiH and Mg. This work has significant impact on the investigation of Li-containing multicomponent systems and the reproducibility of results if different dynamic vacuum conditions are used, as this affects the apparent amount of hydrogen evolved (as determined by ex situ experiments). These results have also helped to explain differences in the reported reversibility of the systems, with Li-rich samples forming a passivating hydride layer, hindering further hydrogenation.

Transverse collective modes in liquid binary alloys

Transverse current correlations in binary liquid alloys are investigated by molecular dynamics simulation. The study includes several Li-Mg, Li-Na and Li-Pb alloys. The characteristics of both shear and transverse optic-like modes are discussed. The former modes are associated with the number density fluctuations whereas the latter are related to the concentration fluctuations. Special attention is paid to the dependence of the results on the mass ratio and composition of the alloy.

Generation of highly porous Li-Mg and Li-Zn alloys from kinetically controlled lithiation

Abstract Li‒Mg and Li‒Zn alloy electrodes are prepared by the kinetically controlled vapour deposition (KCVD) of Li‒Mg and Li‒Zn alloys on a temperature-controlled substrate. The mode of preparation greatly influences the microstructure, surface morphology and electrochemical properties of these Li‒Mg and Li‒Zn alloys. The KCVD technique, as applied to the generation of Li-Mg alloys, establishes the composition of each prepared alloy by independently varying the temperature of the molten lithium, the temperature of a solid magnesium surface with which the lithium interacts, and the temperature of the substrate on which a resulting intimately mixed Li-Mg mixture is deposited. Here, the required temperature for lithium induced magnesium vaporization is more than 200°C below the magnesium melting point. The effect of variable temperature control on the microstructure, morphology and electrochemical properties of the vapour-deposited alloys has been studied and the diffusion coefficients for lithium in the Li‒Mg alloy electrodes prepared by the KCVD method are found to be in the range 1.2–5.2 × 10−7 cm2/s−1 at room temperature. The diffusion coefficients for moderate lithium content alloys, firstly, exceed those for standard alloy preparation and, secondly, are two to three orders of magnitude larger than those for other lithium alloy systems (e.g. 6.0 × 10−10cm2 s−1 in LiA1). A variant of the KCVD technique is used to generate highly porous Li‒Zn alloy films prepared by controlling the temperature of a molten lithium source and the rate at which a zinc source, placed in proximity to the lithium, equilibrates in temperature as the lithium interacts with the zinc. Diffusion coefficients for the Li‒Zn alloy electrodes prepared by this variant of the KCVD method vary from 10−7 to 10−9 cm2 s−1 at room temperature, depending on the alloy composition. This should be compared with the standard alloy whose diffusion coefficient never exceeds 109 cm2 s−1 for any composition. These observations suggest that alloys generated using kinetically controlled lithiation display an enhanced porosity and diffusivity useful for a number of applications.

Generation of highly porous Li‒Mg and Li‒Zn alloys from kinetically controlled lithiation

Abstract Li‒Mg and Li‒Zn alloy electrodes are prepared by the kinetically controlled vapour deposition (KCVD) of Li‒Mg and Li‒Zn alloys on a temperature-controlled substrate. The mode of preparation greatly influences the microstructure, surface morphology and electrochemical properties of these Li‒Mg and Li‒Zn alloys. The KCVD technique, as applied to the generation of Li-Mg alloys, establishes the composition of each prepared alloy by independently varying the temperature of the molten lithium, the temperature of a solid magnesium surface with which the lithium interacts, and the temperature of the substrate on which a resulting intimately mixed Li-Mg mixture is deposited. Here, the required temperature for lithium induced magnesium vaporization is more than 200°C below the magnesium melting point. The effect of variable temperature control on the microstructure, morphology and electrochemical properties of the vapour-deposited alloys has been studied and the diffusion coefficients for lithium in the Li...

Fermiology by Compton Scattering

Recent results on the electron momentum density of simple metals are reviewed to illustrate how Compton scattering is unique and indispensable as a tool to study Fermiology of various materials. Reconstruction of the two- and the three-dimensional momentum density and occupation number density is also reviewed with presenting examples of Li, Li-Mg alloys and Cr.

Densities and molar volumes of solid lithium-magnesium (Li-Mg) alloys

Densities of solid Mg and Li-Mg alloys were measured for five compositions of mole fractions of Li equal to 0.05,0.1,0.15,0.20, and 0.25, respectively, by the dilatometric method. The curvilinear dependence of the density on temperature (room temperature up to 873 K) was observed for all investigated alloys. Results could be described by parabolic equations. The molar volumes of Li-Mg alloys were calculated from the density measurements. It has been found that the densities of solid Li-Mg alloys show positive deviations from linearity, and the molar volumes exhibit negative deviations from linear dependence for all samples in the experimental concentration range. It was possible to describe the dependence of density on temperature and concentration by a polynomial. Coefficients of thermal expansion were calculated and discussed. The density of the (Li) phase along the (Li)/[(Mg) + (Li)] boundary was calculated and described by a temperature-dependent polynomial of the third power.

Static structure and dynamics of the liquid Li-Na and Li-Mg alloys

We present calculations for the static structure and ordering properties of two lithium-based $s\ensuremath{-}p$ bonded liquid alloys, Li-Na and Li-Mg. Our theoretical approach is based on the neutral pseudoatom method to derive the interatomic pair potentials, and on the modified-hypernetted-chain theory of liquids to obtain the liquid static structure, leading to a whole combination that is free of adjustable parameters. The study is complemented by performing molecular dynamics simulations which, besides checking the theoretical static structural results, also allow a calculation of some dynamical properties. The obtained results are compared with the available experimental data.

Electronic structure and bonding of ultralight LiMg

Electronic structure calculation using the Tight Binding Linear Muffin Tin Orbital (TB-LMTO) method has been performed for ultralight LiMg alloys. The band structure, density of states, valence electron charge density and Fermi surface have been computed. The lattice constant, cohesive energy, heat of formation at the equilibrium lattice constant, and bulk modulus are in agreement with available experimental and theoretical results. The calculation shows charge transfer from Mg to Li site in agreement with positron annihilation experiment of Y. Tsuchiya et al. (J. Phys. F8, L29 (1978)).

Concentration dependence of the structure of liquid Li-Na and Li-Mg alloys

Theoretical calculations are presented for the static structure and ordering properties of the Li-Na and Li-Mg liquid alloys. The neutral pseudoatom method is used to derive the interatomic pair potentials and the modified hypernetted chain approximation to obtain the static structure. As a result the overall theory is free of adjustable parameters. Although the two alloys show rather different experimental behaviour, the present theoretical approach is able to reproduce the main structural features of both.

Pressure-induced charge transfer in Li and Al alloys.

In pure metals, the s,p,d, . . . bands have different energy shifts as the metals are compressed. Changes that are produced in this way in the amount of s,p,d, . . . type valence charge affect, e.g., the bonding properties of the atoms, which in turn can lead to structural phase transitions at high pressures. In alloys, the band shifts can produce complex changes in the electronic structure. The present work deals with the pressure-induced charge transfer in alloys. In Li-X alloys (X=Be,Na,Mg,Al,Si,P,Ca,Sr) the number of Li valence electrons is found to increase along with increasing pressure. This is attributed to the properties of Li p states. A similar type of charge transfer is also found in Al-X alloys (X=Ti,Zr,Hf,Cu,Ag,Au). The effects of fully occupied and partially occupied d bands can be studied by considering Al alloyed with noble metals and transition metals. The electronic structure of the alloys is calculated with the linear muffin-tin orbital atomic sphere approximation method. To check the magnitude of the possible computational errors involved in our results we also performed pseudopotential plane-wave calculations for Li-Mg alloys. \textcopyright{} 1996 The American Physical Society.

A first-principles study of the lattice distortion around a solute atom in BCC lithium

In this paper, we study the effect that the lattice distortion around a solute atom (Na, Mg, Al) has on the electronic and mechanical properties of BCC Li using the first-principles structural optimization method. In the present calculations, a 54-site supercell is used to get a better insight into the long-range behaviour of the lattice distortion around a solute atom. The results show that the behaviour of the first-nearest-neighbouring Li shell around a solute atom in all cases investigated is similar to that obtained in the corresponding 16-site supercell calculations. The distortion has, for instance, an effect on the average atomic volume, bulk modulus and heat of formation of Li alloys. From the present calculations, together with our previous studies, we deduce also the concentration dependence of these quantities. For example, the calculated average atomic volume and bulk modulus of dilute Li-Mg alloys, as a function of Mg concentration, agree qualitatively very well with experimental results. Furthermore, the pressure dependence of the lattice distortion is found to be rather important. Our results also predict that the solubility of Na in BCC Li under pressure above 50 kbar is possible.

KKR-CPA calculations of density of states and soft X-ray emission from disordered Li-Mg alloys

The density of state (DOS) and soft X-ray spectra from disordered Li 1− x Mg x alloys have been calculated by using the charge self- consistent KKR-CPA method. We find that the DOS at the Fermi energy ( E F ) shows an interesting behaviour as a function of x; it first increases in the range x = 0.0−0.14, then shows a flat behaviour in the range x⋍0.14−0.20 and finally decreases smoothly from x = 0.20−0.60. We show that this behaviour of the DOS is related to the development of a neck in the Fermi surface and its smearing due to disorder scattering. Theoretical results for the soft X-ray emission spectra are compared with experimental results and are found to be in good accord.