Elemental Lithium Research Articles

Zintl-phase Sr3LiAs2H: crystal structure and chemical bonding analysis by the electron localizability approach.

The compound Sr3 LiAs2 H was synthesized by reaction of elemental strontium, lithium, and arsenic, as well as LiH as hydrogen source. The crystal structure was determined by single-crystal X-ray diffraction: space group Pnma; Pearson symbol oP28; a = 12.0340(7), b = 4.4698(2), c = 12.5907(5) Å; V = 677.2(1) Å(3) ; RF = 0.047 for 1021 reflections and with 36 parameters refined. The positions of the hydrogen atoms were first revealed by the electron localizability indicator and subsequently confirmed by crystal structure refinement. In the crystal structure of Sr3 LiAs2 H the metal atoms are arranged in a Gd3 NiSi2 -type motif, whereas the hydrogen atoms are arranged in a distorted tetrahedral environment formed by strontium. The calculated band structure revealed that Sr3 LiAs2 H is a semiconductor, which is in agreement with its diamagnetic behavior. Thus, Sr3 LiAs2 H is considered as a (charge-balanced) Zintl phase.

Molecular ion battery: a rechargeable system without using any elemental ions as a charge carrier.

Is it possible to exceed the lithium redox potential in electrochemical systems? It seems impossible to exceed the lithium potential because the redox potential of the elemental lithium is the lowest among all the elements, which contributes to the high voltage characteristics of the widely used lithium ion battery. However, it should be possible when we use a molecule-based ion which is not reduced even at the lithium potential in principle. Here we propose a new model system using a molecular electrolyte salt with polymer-based active materials in order to verify whether a molecular ion species serves as a charge carrier. Although the potential of the negative-electrode is not yet lower than that of lithium at present, this study reveals that a molecular ion can work as a charge carrier in a battery and the system is certainly a molecular ion-based “rocking chair” type battery.

Lithium Sulfide/Carbon (Li2S/C) Electrode Preparation in Hydrogen Sulfide (H2S) Flow and Its Electrochemical Performance

Energy storage for automotive and portable devices is one of the main research topics today and in the future. Today’s batteries based on Li-ion technology are not up to par with the demands of long-range vehicles[1]. The solutions to this problem are beyond Li-ion technologies, e.g. Li/S or Li/air. Possible distances of >400 km or >550 km for Li/S or Li/air, respectively, compared to today’s 160 km with Li-ion technology are desirable[2]. The biggest obstacle in Li/S and Li/air batteries are safety concerns due to the use of elemental lithium as anode material[3]. This may be overcome by using a Li2S cathode, equivalent to the discharged state of the Li/S battery, and a lithium free anode such as carbon. Since Li2S is very moisture sensitive, preparation of Li2S electrodes needs to be in a very controlled environment. We invented a new method to produce Li2S/C electrodes in a H2S flow, by using various lithium salts as starting materials. This way the air-sensitive Li2S is introduced in the electrode in the very last step. This lowers the process costs and allows an easier handling of the electrodes during preparation, since it is less moisture sensitive. Furthermore it might allow the use of aqueous binder systems which is novel for Li2S electrodes. Electrodes containing a lithium salt, carbon and a binder were cast and after drying exposed to H2S. The resulting electrode consists of lithium sulfide, carbon and the binder. The reaction is confirmed by X-ray diffraction and elemental analysis. The morphology and homogeneity of the electrode is investigated by scanning electron microscopy. Galvanostatic cycling of the Li2S/C electrode validates the new method. [1] X. Ji, L.F. Nazar, Advances in Li–S batteries, Journal of Materials Chemistry, 20 (2010) 9821. [2] P.G. Bruce, S.A. Freunberger, L.J. Hardwick, J.M. Tarascon, Li-O2 and Li-S batteries with high energy storage, Nature materials, 11 (2012) 19-29. [3] J.M. Tarascon, M. Armand, Issues and challenges facing rechargeable lithium batteries, Nature, 414 (2001) 359-367.

A Saturated and Unsaturated Backbone of the Products from the Reaction of 1, 2‐Diimine with Aluminum Precursors

Abstract An aluminum(III) monohydride [(2, 6‐iPr2C6H3)NC(Me)]2AlH(NMe3) (1) was synthesized by oxidative addition of 1, 2‐diimine (L) {L = [(2, 6‐iPr2C6H3)NC(Me)]2} with equivalent amounts of H3Al·NMe3. A lithium salt (LLi2) was obtained when L was treated with elemental lithium. Under these conditions 1, 2‐diimine is reduced to LLi2 with simultaneous formation of a C=C bond. The LLi2 is formed in‐situ and treated with AlBr3 to result in the formation of aluminum(III) monobromide [(2, 6‐iPr2C6H3)NC(Me)]2AlBr(OEt2) (2). The two products 1 and 2 show a saturated as well as an unsaturated backbone of the ligand.

A new tetragonal structure type for Li2B2C.

The ternary dilithium diboron carbide, Li2B2C (tetragonal, space group P-4m2, tP10), crystallizes as a new structure type and consists of structural fragments which are typical for structures of elemental lithium and boron or binary borocarbide B13C2. The symmetries of the occupied sites are .m. and 2mm. for the B and C atoms, and -4m2 and 2mm. for the Li atoms. The coordination polyhedra around the Li atoms are cuboctahedra and 15-vertex distorted pseudo-Frank-Kasper polyhedra. The environment of the B atom is a ten-vertex polyhedron. The nearest neighbours of the C atom are two B atoms, and this group is surrounded by a deformed cuboctahedron with one centred lateral facet. Electronic structure calculations using the TB-LMTO-ASA method reveal strong B...C and B...B interactions.

Lithium Plating on Graphite Negative Electrodes: Innovative Qualitative and Quantitative Investigation Methods

The effect of metallic lithium depositing on the negative electrode surface of a carbon-based lithium-ion battery instead of intercalating into the graphitic layers, namely lithium plating, can be assigned to charging at low temperatures and/or high currents. Cell parameters, such as performance and safety, are negatively influenced by this phenomenon. Elemental lithium deposited on the negative electrode requires more space than the intercalated compound and therefore increases the cell volume. Thus, the thickness changes during cycling can be used as a qualitative indicator for lithium plating. In this context, two different non-destructive experimental setups detecting the thickness profiles in situ are presented. Moreover, a quantitative titration technique to determine the exact amount of lithium deposited is established.

Silicon Nitride Coated Silicon Thin Films As Anodes for Li-Ion Batteries

Silicon has proven to have a great potential as anode material in lithium-ion batteries due to its high theoretical electrochemical capacity. However, silicon anodes deteriorate quickly during cyclic charging and discharging, rendering them useless in only a few cycles [1]. This has been attributed to the stresses induced by the large volume change of the material during cycling. Numerous attempts have been made to reduce these stresses, e.g. by using nanoparticles, nanorods, nanowires, thin films and porous structures, with a varying degree of success [2, 3]. While using finely structured materials aids in the intercalation of lithium by reducing the necessary diffusion distance, it also has the unfortunate effect of greatly increasing the specific surface area of the silicon. When using nano-sized materials, silicon’s ability to form a thin and stable solid electrolyte interphase (SEI) therefore becomes increasingly important. There are a number of factors that have a large influence on the SEI formation, making the process notoriously difficult to analyze, but also makes it possible to manipulate. Coating silicon with different nitrides and oxides, e.g. TiN and TiO, have previously been shown to enhance the cycling stability and Coulombic efficiency of the material [4, 5]. In this project the effect of coating the surface of silicon thin films with a thin (< 4-5 nm) layer of silicon nitride is investigated, as well as the effect of varying the stoichiometry of the silicon nitride. By itself silicon nitride has been shown to function as a conversion electrode material, forming elemental silicon and lithium nitride during the initial cycle, with thin films exhibiting capacities of up to 1800 mAh/g [6].40 nm silicon thin films were deposited by PECVD on copper foil using silane as precursor. The nitride was formed by addition of ammonia to the gas flow in the late stages of the deposition, and different stoichiometries were obtained by changing the ratio of these gases. By varying the flow rate of ammonia, coatings with four different compositions were made; pure silicon (A), stoichiometric Si3N4(D) and two intermediate compositions (B and C). Three electrodes were punched from each of the resulting films and mounted in coin cells with lithium metal counter electrodes and cycled at a current rate of C/3 for 150 cycles. During cycling, all the cells exhibited an initial increase in capacity, peaking at close-to-theoretical capacity within 10-40 cycles before beginning a slow decline. The average charge capacity for each series after 50, 100 and 150 cycles is presented in the figure, showing that the capacity retention increases with increasing nitrogen content for series A, B and C, and then decreases for series D. This indicates that a nitrogen coating has a positive effect on the deterioration mechanisms of the electrode, and that this effect increases with increasing nitrogen content of the coating, as long as a stoichiometric nitride is not formed.1. Kasavajjula, U., C. Wang, and A.J. Appleby, Nano-and bulk-silicon-based insertion anodes for lithium-ion secondary cells. Journal of Power Sources, 2007. 163(2): p. 1003-1039.2. Wu, H. and Y. Cui, Designing nanostructured Si anodes for high energy lithium ion batteries. Nano Today, 2012. 7(5): p. 414-429.3. Ge, M., et al., Scalable preparation of porous silicon nanoparticles and their application for lithium-ion battery anodes.Nano Research, 2013: p. 1-8.4. Memarzadeh Lotfabad, E., et al., ALD TiO2 coated silicon nanowires for lithium ion battery anodes with enhanced cycling stability and coulombic efficiency. Physical chemistry chemical physics : PCCP, 2013. 15(32): p. 13646-57.5. Kohandehghan, A., et al., Silicon nanowire lithium-ion battery anodes with ALD deposited TiN coatings demonstrate a major improvement in cycling performance. Journal of Materials Chemistry A, 2013. 1(41): p. 12850-12861.6. Suzuki, N., et al., Silicon nitride thin film electrode for lithium-ion batteries. Journal of Power Sources, 2013. 231(0): p. 186-189.

Transition Metal‐Depleted Graphenes for Electrochemical Applications via Reduction of CO2 by Lithium

Graphene has immense potential for future applications in the electrochemical field, such as in supercapacitors, fuel cells, batteries, or sensors. Graphene materials for such applications are typically fabricated through a top-down approach towards oxidation of graphite to graphite oxide, with consequent exfoliation/reduction to yield reduced graphenes. Such a method allows the manufacture of graphenes in gram/kilogram quantities. However, graphenes prepared by this method can contain residual metallic impurities from graphite which dominate the electrochemical properties of the graphene formed. This dominance hampers their electrochemical application. The fabrication of transition metal-depleted graphene is described, using ultrapure CO₂ (with benefits of low cost and easy availability) and elemental lithium by means of reduction of CO₂ to graphene. This preparation method produces graphene of high purity with electrochemical behavior that is not dominated by any residual transition metal impurities which would dramatically alter its electrochemical properties. Wide application of such methodology in industry and research laboratories is foreseen, especially where graphene is used for electrochemical devices.

High-pressure synthesis of lithium hydride

By compressing elemental lithium and hydrogen in a diamond anvil cell, we have synthesized lithium hydride (LiH) at pressures as low as 50 MPa at room temperature. Combined Raman spectroscopy and synchrotron x-ray diffraction measurements reveal that, once synthesized, LiH remains stable at 300 K up to 160 GPa in the presence of molecular hydrogen. The mixture of lithium hydride and molecular hydrogen and application of pressure alone cannot form a higher H${}_{2}$ content hydride (LiH${}_{x}$, $x&gt;1$) as was suggested from the theoretical ab initio calculations and therefore, cannot be considered as a route to low-pressure hydrogen rich material metallization.

Nanostructured β-Li3PS4 for All-Solid Lithium-Sulfur Batteries

not Available.

Endocyclic P–P bond cleavage in carbaborane-substituted 1,2-diphosphetane: a new route to secondary phosphinocarbaboranes

Carbaborane-substituted 1,2-diphosphetane reacts with elemental lithium and hydrogen chloride to give exclusively secondary mono- and bis(phosphino)carbaboranes. The latter reacts with two equivalents of formaldehyde and one equivalent of aniline to give a carbaborane-substituted 1-aza-3,6-diphosphepane.

Ion transport and phase transition in Li7−xLa3(Zr2−xMx)O12(M = Ta5+, Nb5+, x = 0, 0.25)

Due to their favourable combination of high ionic conductivity and stability versus elemental lithium, garnet-related lithium ion conductors Li7La3Zr2O12 have raised strong interest for both all-solid-state batteries and as protective layers for anode materials. Here we study the correlation between structure and ion mobility in Li7−xLa3(Zr2−xMx)O12 (x = 0, 0.25; M = Ta5+, Nb5+) combining Molecular Dynamics (MD) simulations, bond valence (BV) studies and experimental characterisation. In situXRD demonstrates a tetragonal-to-cubic phase transition above 450 K for LixLa3Zr2O12. MD simulations using our new BV-based Morse-type force field reproduce static (lattice constants, thermal expansion, phase transition) and dynamic characteristics of this material. Simulations and structure refinements for the tetragonal phase accordingly yield an ordered Li distribution. The majority of Li fully occupies the 16f and 32g octahedral sites. Out of the two tetrahedral sites only the 8a site is fully occupied leaving the 16e tetrahedral sites with slightly higher site energy due to the tetragonal distortion vacant. For the cubic phase recent structural studies either suggest a major Li+ redistribution to nearly fully occupied tetrahedral sites and distorted octahedral sites with a low occupancy (which leads to unphysically short Li–Li distances) or suggest the existence of additional Li sites. MD simulations however show that the lithium distribution just above the phase transition closely resembles that in the tetragonal phase with only slightly more than 1/3 of the now equivalent tetrahedral 24d sites and almost half of the distorted octahedral 96h sites occupied, so that overly short Li–Li distances are avoided. Pentavalent doping enhances ionic conductivity by increasing the vacancy concentration and by reducing local Li ordering. At higher temperatures Li is gradually redistributed to the tetrahedral sites that can be occupied up to a site occupancy factor of 0.56. BV pathway analysis and closely harmonizing Li trajectories demonstrate that the two partially occupied Li sites of similar site energy form a 3D network suitable for fast ion conduction. The simulated diffusion coefficient and its activation energy closely match the experimental conductivities. The degree of correlation of the vacancy-type Li+ ion migration is analyzed in terms of the van Hove correlation function.

Shorter and Easier Syntheses of Di‐tert‐butylketene and Relatedgem‐Di‐tert‐butyl Compounds

AbstractThe ketenetBu2C=C=O is prepared fromtBu2C=O in three steps (performable as a two‐stage operation) through elimination of HCl from the intermediate producttBu2CCl–CH=O. The acidtBu2CH–CO2H, obtainable in two, three, or four preparative stages fromtBu2C=O, adds slowly to the ketene to produce the anhydride (tBu2CH–CO)2O. Elemental lithium together with ClSiMe3convertstBu2CCl–CH=O intotBu2C=CH–OSiMe3, which is a durable precursor oftBu2CH–CH=O, making this aldehyde easily and cheaply available fromtBu2C=O. By exclusion of alternative mechanistic possibilities, the reduction oftBu2CCl–CH=O bytBuMgCl is shown to involve at least one single‐electron transfer, leading to the enolatetBu2C=CH–OMgCl, which can be converted intotBu2CH–CH=O (three steps fromtBu2C=O) or intotBu2C=CH–OSiMe3. Hydride transfer from NaBH4totBu2CCl–CH=O affordstBu2CCl–CH2OH, the transformations of which provide an entertaining set of SN1‐type reactions. Several other examples of carbenium‐type behavior are encountered in thisgem‐tBu2system; they are attributed to steric congestion, which also impedes bond rotations in the anhydride and in two esters. A convenient route totBu2CH–C≡N (five steps fromtBu2C=O) uses the conversion oftBu2C=CH–OSiMe3intotBu2CH–CH=NOH. The slow thermal (Z)/(E) equilibration oftBu2CH–NH–CH=O reveals the ranking of ecliptic repulsions as H3C &lt;tBu &lt;tBu2CH.

Fe II/Fe III mixed-valence state induced by Li-insertion into the metal-organic-framework Mil53(Fe): A DFT+U study

The iron-based metal-organic-framework MIL53(Fe) has recently been tested as a cathode materials for Li-Ion batteries, leading to promising cycling life and rate capability. Despite a poor capacity of 70 mAh g −1 associated with the exchange of almost 0.5Li/Fe, this result is the first evidence of a reversible lithium insertion never observed in a MOF system. In the present study, the MIL53(Fe) redox mechanism is investigated through first-principles DFT+U calculations. The results show that MIL53(Fe) is a weak antiferromagnetic charge transfer insulator at T = 0 K, with iron ions in the high-spin S = 5/2 state. Its reactivity vs elemental lithium is then investigated as a function of lithium composition and distribution over the most probable Li-sites of the MOF structure. The redox mechanism is fully interpreted as a two-step insertion/conversion mechanism, associated with the stabilization of the Fe 3+/Fe 2+ mixed-valence state prior to the complete decomposition of the inorganic–organic interactions within the porous MOF architecture.

A simple apparatus for the injection of lithium aerosol into the scrape-off layer of fusion research devices

A simple device has been developed to deposit elemental lithium onto plasma facing components in the National Spherical Torus Experiment. Deposition is accomplished by dropping lithium powder into the plasma column. Once introduced, lithium particles quickly become entrained in scrape-off layer flow as an evaporating aerosol. Particles are delivered through a small central aperture in a computer-controlled resonating piezoelectric disk on which the powder is supported. The device has been used to deposit lithium both during discharges as well as prior to plasma breakdown. Clear improvements to plasma performance have been demonstrated. The use of this apparatus provides flexibility in the amount and timing of lithium deposition and, therefore, may benefit future fusion research devices.

N-Heterocyclic Germylidenide and Stannylidenide Anions: Group 14 Metal(II) Cyclopentadienide Analogues

The reaction of a sterically bulky β-diketiminato lithium complex [Li(ButNacnac)] (ButNacnac = [{N(Dip)C(But)}2CH]−, Dip = C6H3Pri2-2,6) with GeCl2·dioxane has given the germanium(II) chloride complex [(ButNacnac)GeCl] (3). Both it and its known tin analogue, [(ButNacnac)SnCl] (4), were crystallographically characterized and found to be monomeric in the solid state. The reduction of both complexes with elemental lithium in THF led to lithium complexes of N-heterocyclic germylidenide and stannylidenide anions, viz., [(THF)Li{η5-EC(But)C(H)C(But)N(Dip)}] (E = Ge, 5; Sn, 6). The reduction of the germanium(II) precursor, 3, also afforded the germanium(II) amide complex [(ButNacnac)Ge{N(H)(Dip)}] (7). The mechanisms of formation of the complexes are thought to involve a number of steps, including reductive ring contraction reactions. The crystallographic and spectroscopic data for [(THF)Li{η5-EC(But)C(H)C(But)N(Dip)}] indicate a significant degree of aromatic π-delocalization within their heterocycles.

Easier Preparation of 2,6-Di-tert-butylphenyl Derivatives¹

Despite steric shielding by the 2,6-di-tert-butylphenyl group (‘super-2,6-xylyl’ = xyl*), inexpensive sodium phenolate (xyl*-ONa) reacts with dimethyl sulfate to produce only xyl*-OCH3 (94%) with complete suppression of the alternative 4-methylation. Reductive cleavage of xyl*-OCH3 by elemental lithium with the help of an electron carrier generates xyl*-Li, which in turn yields xyl*-CO2H (63%). The corresponding 4-methyl-derivatives of these compounds were obtained analogously. The acid chloride xyl*-COCl (77% yield) acylates HalMgCH2R to give only xyl*-COCH3 (86%) or xyl*-COEt (97%). These two ketones react with n-butyllithium (no carbonyl addition) and Cl-PO(OEt)2 to furnish only the enol phosphates xyl*-C(=CH2)OPO(OEt)2 (84%) or xyl*-C(=CHCH3)OPO(OEt)2 (up to 70%), respectively. Only 1,2-elimination occurs when the latter two products are treated with tert-butyllithium, affording xyl*-C≡CH (68%) or xyl*-C≡CMe (88%), respectively.

Design of Electrode Materials for Lithium-Ion Batteries: The Example of Metal−Organic Frameworks

In the field of energy storage and Li-ion batteries, searching for new (positive) electrode materials with better electrochemical performances than those of transition-metal oxides is of permanent concern. To that aim, very simple concepts of chemical bonding can be used to find out the origin of the electrode limitations and to guide experimentalists for the design of new promising materials. This local approach was recently applied to hybrid architectures, such as metal−organic frameworks (MOFs), and allowed some of us to demonstrate the first reversible lithium insertion into the MIL53(Fe) positive electrode. In this paper, we combine first-principles density functional calculations and local chemical bond analyses to fully interpret the redox mechanism of this material. Its reactivity versus elemental lithium is investigated as a function of (i) the lithium composition from xLi/Fe = 0−1, (ii) the lithium distribution over the most probable Li sites, and (iii) the OH/F substitution ratio along the redo...

The competition between Si–Si and Si–C cleavage in functionalised oligosilanes: their reactivity with elemental lithium

The reaction of aryl-substituted disilanes with elemental lithium is a common method for the preparation of lithiosilanes and the subsequent synthesis of functionalised oligosilanes, especially of enantiomerically pure compounds. A series of alkyl- and arylsubstituted di- and trisilanes has been investigated with respect to their reactivity against elemental lithium. Thereby, depending on the substituents, silicon-silicon bond cleavage of the central Si-Si unit and/or silicon-carbon bond cleavage to arenes are observed. Quantum chemical studies provide a deeper insight into the ongoing processes. The reactive centre can be estimated by both, bond elongation after electron transfer and frontier orbital interactions (pi-bonding and sigma-antibonding part). Aromatic substituents at the silicon atoms proved to be necessary for the processing of any cleavage reaction in the studied systems by stabilising the radical anion after electron transfer at the corresponding di- or trisilane. Yet, selective cleavage reactions do not depend on the number of arenes.

Synthesis and characterization of three new thermally stable N-heterocyclic germylenes

Abstract Three new stable germylenes, rac -1,3-di- tert -butyl-4,5-dimethyl-1,3-diaza-2-germacyclopentane-2-ylide ( 1 ), 1,3-di- tert -butyl-4,4-dimethyl-1,3-diaza-2-germacyclopentane-2-ylide ( 2 ), and rac -1,3,4-tri- tert -butyl-1,3-diaza-2-germacyclopentane-2-ylide ( 3 ) have been synthesized by the reaction of their corresponding germyl dichlorides with elemental lithium. Full synthetic procedures and characterizations are described.