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Results for “lithium clusters”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Theoretical studies of the global minima and polarizabilities of small lithium clusters

Lithium clusters Lin (n=1-20) have been investigated with density functional theory (DFT) and coupled—cluster (CC) methods. The global-minimum structures are located via an improved basin---hopping algorithm and the lowest energy Lin isomers are confirmed with DFT geometry optimizations, CCSD(T) energy calculations, and by comparing simulated and experimental polarizabilities. The tetrahedral Li4 structure is found to be the basic building block of lithium clusters Lin (n=6-20). Simulated polarizabilities, including thermal effects at room temperature, are in good agreement with measured isotropic polarizabilities.

clusters↗
DOE OSTI2019

Generation of Lithium Clusters in Helium Plasma Flow

The formation of lithium clusters in a helium flow is considered within the method considering the widths of energy levels. It is shown that lithium atoms in a plasma flow of inert helium form a cluster consisting of lithium only. In addition to lithium clusters with interatomic distances corresponding to interatomic distances of the equilibrium state, long-lived excitations of clusters with interatomic distances of 13 Bohr radii are observed. However, if excitations are removed, such systems transfer into the ground state or decay. In addition, it is observed that Li–He systems are long-lived under conditions of external excitations but quickly lose helium when these excitations are removed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Engineering Redox Potential of Lithium Clusters for Electrode Material in Lithium-Ion Batteries

Low negative electrode potential and high reactivity makes lithium (Li) ideal candidate for obtaining highest possible energy density among other materials. Here, we show a novel route with which the overall electrode potential could significantly be enhanced through selection of cluster size. In using first principles density functional theory and continuum dielectric model, we studied free energy and redox potential as well as investigated relative stability of Li n (n ≤ 8) clusters in both gas phase and solution. We found that Li 3 has the lowest negative redox potential (thereby highest overall electrode potential) suggesting that cluster based approach could provide a novel way of engineering the next generation battery technology. The microscopic origin of Li 3 cluster’s superior performance is related to two major factors: gas phase ionization and difference between solvation free energy for neutral and positive ion. Taken together, our study provides insight into the engineering of redox potential in battery and could stimulate further work in this direction.

25 ENERGY STORAGE↗
DOE OSTI2016

Dissociation of doubly charged clusters of lithium acetate: Asymmetric fission and breakdown of the liquid drop model: Dissociation of doubly charged clusters of lithium acetate

Unimolecular and collision-induced dissociation of doubly charged lithium acetate clusters, (CH3COOLi)nLi22+, demonstrated that Coulomb fission via charge separation is the dominant dissociation process with no contribution from the neutral evaporation processes for all such ions from the critical limit to larger cluster ions, although latter process have normally been observed in all earlier studies. These results are clearly in disagreement with the Rayleigh’s liquid drop model that has been used successfully to predict the critical size and explain the fragmentation behavior of multiply charged clusters.

Cluster Ions↗
DOE OSTI2018

Energetics of Lithium Insertion into Magnetite, Defective Magnetite, and Maghemite

At low concentrations of lithium insertion into inverse spinel magnetite Fe 3 O 4 , a phase change to rock-salt-like Li x Fe 3 O 4 has been observed. Here, we used density-functional-theory-based (DFT-based) calculations to study the structural origins of this phase change, the concentration at which it occurs, the role of iron vacancies, and the stability of the various motifs that form during the electrochemical reduction process in the Li–Fe–O ternary space up to x = 1.33. We compared our results to new experimental measurements of the open circuit voltage for 8–9 nm magnetite particles over a comparable range of lithium insertion. Of the vacant sites in magnetite (16c, 8b, and 48f) lithium insertion was found to be most stable on 16c. Coulomb interactions between the added lithium and iron at the 8a site in magnetite led to substantial displacement of the iron. As further lithium was added, the most energetically favored motif involved lithium clustering in 16c sites around the shifted 8a iron up to a total of three lithiums. In competition with the lithium clustering motif, lithium insertion could be accompanied by the full displacement of all 8a iron to 16c sites, to form the rock-salt-like Li x Fe 3 O 4 , saturating at x = 1. The defective rock-salt structure was found to be more stable than the lithium clustering motif for x ≥ 0.5. The rock-salt-like LiFe 3 O 4 was found to be stable in the Li–Fe–O ternary space for a continuous range of Li–Fe organization on the 16c sites, stabilized by Coulomb interactions. For x < 1, neither the lithium clustering motif, nor the defective rock-salt-like structure for LixFe 3 O 4 were stable against phase segregation to LiFe 3 O 4 and Fe 3 O 4 . This phase segregation (0 < x < 1) occurred at a predicted voltage of ~2.0 V. However, when iron vacancies on the 16d site were introduced, lithium insertion to those vacant 16d sites in Fe 2.875 O 4 , and γ-Fe 2.67 O 4 (maghemite), resulted in stable intercalated materials at a predicted voltage of ~3.0 V. Beyond the concentration of such iron vacancy sites, phase segregation was predicted to the rock-salt-like Li 1.125 Fe 2.875 O 4 and Li 1.33 Fe 2.67 O 4 , again at ~2.0 V. These results were consistent with measured open circuit voltages. Finally, the relative stability for several lithium compositions along the FeO to LiFeO 2 tie line in the defective rock-salt structure suggested stable compound formation for a range of lithium–iron compositions, but without long-range order in the cation sublattice, consistent with what has been commonly observed in the literature.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Oxidative decomposition mechanisms of lithium peroxide clusters: an Ab Initio study

Oxidative decomposition of solid lithium peroxide is an important part of the charging process in a Li-O 2 battery. Here, we investigate oxidative decomposition mechanisms of lithium peroxide clusters as molecular models for solid lithium peroxide using density functional methods to understand charging processes in advanced energy storage systems. Most calculations are done using a (Li 2 O 2 ) 4 cluster with similar results obtained from a larger (Li 2 O 2 ) 16 cluster. Reaction pathways of the clusters involving different sequences of oxidation, oxygen evolution, lithium cation removal, and spin excitation are investigated. The computations suggest that certain oxidative decomposition routes may not have dependence on the oxygen evolution or Li-ion removal kinetics due to the exothermicity of oxygen removal and Li + removal (by solvent) upon oxidation. The computed charge potentials evaluated using a tetramer model indicates that it is possible to have low overcharge potential provided there exists a good electronic conductivity to facilitate the oxidative decomposition. Finally, oxidation potentials of a series of Li x O y clusters are investigated to assess their dependence on stoichiometry and how the local site from which the electrons are being removed affects the charge potentials.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2015

Lithium formate ion clusters formation during electrospray ionization: Evidence of magic number clusters by mass spectrometry and ab initio calculations

Small cationic and anionic clusters of lithium formate were generated by electrospray ionization and their fragmentations were studied by tandem mass spectrometry (collision-induced dissociation with N{sub 2}). Singly as well as multiply charged clusters were formed in both positive and negative ion modes with the general formulae, (HCOOLi){sub n}Li{sup +}, (HCOOLi){sub n}Li{sub m}{sup m+}, (HCOOLi){sub n}HCOO{sup −}, and (HCOOLi){sub n}(HCOO){sub m}{sup m−}. Several magic number cluster (MNC) ions were observed in both the positive and negative ion modes although more predominant in the positive ion mode with (HCOOLi){sub 3}Li{sup +} being the most abundant and stable cluster ion. Fragmentations of singly charged positive clusters proceed first by the loss of a dimer unit ((HCOOLi){sub 2}) followed by the loss of monomer units (HCOOLi) although the former remains the dominant dissociation process. In the case of positive cluster ions, all fragmentations lead to the magic cluster (HCOOLi){sub 3}Li{sup +} as the most abundant fragment ion at higher collision energies which then fragments further to dimer and monomer ions at lower abundances. In the negative ion mode, however, singly charged clusters dissociated via sequential loss of monomer units. Multiply charged clusters in both positive and negative ion modes dissociated mainly via Coulomb repulsion. Quantum chemical calculations performed for smaller cluster ions showed that the trimer ion has a closed ring structure similar to the phenalenylium structure with three closed rings connected to the central lithium ion. Further additions of monomer units result in similar symmetric structures for hexamer and nonamer cluster ions. Thermochemical calculations show that trimer cluster ion is relatively more stable than neighboring cluster ions, supporting the experimental observation of a magic number cluster with enhanced stability.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Organization of Lithium Cubane Clusters into Three-Dimensional Porous Frameworks by Self-Penetration and Self-Polymerization

Metal–organic frameworks based on lithium inherit the unique chemical and structural features of the metal ion itself. While the monomeric lithium node, usually 4-connected, is very desirable for designing zeolite-type networks, the resulting lithium MOF usually has limited stability, especially for 3-connected nets due to the solvent termination. The conventional design strategy based on lithium aryloxide clusters makes use of phenol-type ligands for cluster formation and a separate bifunctional ligand for cross-linking, which also leads to 4-connected nets. By integrating the roles of cluster-formation and framework-formation into a single ligand, 4-hydroxypyridine was previously shown to give a highly stable 8-connected framework. Still, its shortness and rigidity limit both the porosity and the type of framework topologies. Here, we demonstrate the new chemical and structural features of lithium cubane clusters with an elongated ligand, which results in two high-connected 3-D framework materials characterized by self-penetration and self-polymerization, respectively, unlike the commonly observed interpenetration. Such a method provides a feasible path to tune both stability and porosity in lithium-based MOFs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Presence of Li clusters in molten LiCl-Li

Molten mixtures of lithium chloride and metallic lithium are of significant interest in various metal oxide reduction processes. These solutions have been reported to exhibit seemingly anomalous physical characteristics that lack a comprehensive explanation. ln the current work, the physical chemistry of molten solutions of lithium chloride and metallic lithium, with and without lithium oxide, was investigated using in situ Raman spectroscopy. The Raman spectra obtained from these solutions were in agreement with the previously reported spectrum of the lithium cluster, Li 8 . Furthermore, this observation is indicative of a nanofluid type colloidal suspension of Li 8 , in a molten salt matrix. It is suggested that the formation and suspension of lithium clusters in lithium chloride is the cause of various phenomena exhibited by these solutions that were previously unexplainable.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Structure and Stability of Lithium Superoxide Clusters and Relevance to LiO2 Batteries

The discharge mechanism of a Li-O-2 battery involves lithium superoxide (LiO2) radicals. In this Letter, we have performed high-level quantum chemical calculations (G4MP2) to investigate the structure and stability of LiO2 clusters. The clusters have planar ring-shaped structures, high spins, and are thermodynamically more stable than LiO2 dimer. The computed energy barrier for disproportionation of the larger clusters is also significantly higher than the corresponding barrier in the LiO2 dimer (1.0 eV vs 0.5 eV). This means that disproportionation rate should be much slower if the reaction involves LiO2 clusters other than the dimer. As a result, the clusters may survive long enough to be incorporated into the growing discharge product. These results are discussed in terms of recent experimental studies of the electronic structure and morphology of the discharge products in Li-air batteries.

Das, Ujjal↗
DOE OSTI2014

Effect of the size-selective silver clusters on lithium peroxide morphology in lithium–oxygen batteries

Lithium–oxygen batteries have the potential needed for long-range electric vehicles, but the charge and discharge chemistries are complex and not well understood. The active sites on cathode surfaces and their role in electrochemical reactions in aprotic lithium–oxygen cells are difficult to ascertain because the exact nature of the sites is unknown. In this paper, we report the deposition of subnanometre silver clusters of exact size and number of atoms on passivated carbon to study the discharge process in lithium–oxygen cells. The results reveal dramatically different morphologies of the electrochemically grown lithium peroxide dependent on the size of the clusters. This dependence is found to be due to the influence of the cluster size on the formation mechanism, which also affects the charge process. Finally, the results of this study suggest that precise control of subnanometre surface structure on cathodes can be used as a means to improve the performance of lithium–oxygen cells.

25 ENERGY STORAGE↗
DOE OSTI2024

Cellulose acetate membranes exhibit exceptional monovalent to divalent cation selectivities

Salt transport properties of cellulose acetate membranes are reported for a series of chloride salts with mono- valent and divalent cations (LiCl, NaCl, MgCl 2 , CaCl 2 ). Measurements include salt permeability and sorption, with diffusivity values calculated from the permeability and sorption results. We report an exceptionally high LiCl/MgCl 2 selectivity of 750:1. Salts with similar valence (LiCl and NaCl; MgCl 2 and CaCl 2 ) have similar transport properties. The high monovalent/divalent selectivity arises from differences in both sorption and diffusion, with a LiCl/MgCl 2 solubility selectivity of about 11 and a diffusivity selectivity of about 70. Atomistic molecular dynamics simulations show that ions tend to reside in isolated clusters of water. Increasing ion charge strengthens ion–water interactions relative to ion–polymer interactions, explaining the reduced sorption of divalent ions. Diffusion of ions through the membrane occurs via hop-like motion between water clusters. Lithium diffuses faster than magnesium due to weaker ion–water coordination for lithium, which allows for greater mobility within water clusters and more frequent hopping. Altogether, our atomistic simulations suggest that the high LiCl/MgCl 2 selectivity is linked to cellulose acetate’s high water/salt selectivity and is a consequence of low water content and relatively uniform water distribution.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Ferromagnetic bond of Li{sub 10} cluster: An alternative approach in terms of effective ferromagnetic sites

In this work, a model to explain the unusual stability of atomic lithium clusters in their highest spin multiplicity is presented and used to describe the ferromagnetic bonding of high-spin Li{sub 10} and Li{sub 8} clusters. The model associates the (lack of-)fitness of Heisenberg Hamiltonian with the degree of (de-)localization of the valence electrons in the cluster. It is shown that a regular Heisenberg Hamiltonian with four coupling constants cannot fully explain the energy of the different spin states. However, a more simple model in which electrons are located not at the position of the nuclei but at the position of the attractors of the electron localization function succeeds in explaining the energy spectrum and, at the same time, explains the ferromagnetic bond found by Shaik using arguments of valence bond theory. In this way, two different points of view, one more often used in physics, the Heisenberg model, and the other in chemistry, valence bond, come to the same answer to explain those atypical bonds.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Electrical resistance of the current collector controls lithium morphology

Abstract The electrodeposition of low surface area lithium is critical to successful adoption of lithium metal batteries. Here, we discover the dependence of lithium metal morphology on electrical resistance of substrates, enabling us to design an alternative strategy for controlling lithium morphology and improving electrochemical performance. By modifying the current collector with atomic layer deposited conductive (ZnO, SnO 2 ) and resistive (Al 2 O 3 ) nanofilms, we show that conductive films promote the formation of high surface area lithium deposits, whereas highly resistive films promote the formation of lithium clusters of low surface area. We reveal an electrodeposition mechanism in which radial diffusion of electroactive species is promoted on resistive substrates, resulting in lateral growth of large (150 µm in diameter) planar lithium deposits. Using resistive substrates, similar lithium morphologies are formed in three distinct classes of electrolytes, resulting in up to ten-fold improvement in battery performance. Ultimately, we report anode-free pouch cells using the Al 2 O 3 -modified copper that maintain 60 % of their initial discharge capacity after 100 cycles, displaying the benefits of resistive substrates for controlling lithium electrodeposition.

25 ENERGY STORAGE↗
DOE OSTI2016

A constraint on the formation timescale of the young open cluster NGC 2264: lithium abundance of pre-main sequence stars

The timescale of cluster formation is an essential parameter in order to understand the formation process of star clusters. Pre-main sequence (PMS) stars in nearby young open clusters reveal a large spread in brightness. If the spread were considered to be a result of a real spread in age, the corresponding cluster formation timescale would be about 5–20 Myr. Hence it could be interpreted that star formation in an open cluster is prolonged for up to a few tens of Myr. However, difficulties in reddening correction, observational errors, and systematic uncertainties introduced by imperfect evolutionary models for PMS stars can result in an artificial age spread. Alternatively, we can utilize Li abundance as a relative age indicator of PMS star to determine the cluster formation timescale. The optical spectra of 134 PMS stars in NGC 2264 have been obtained with MMT/Hectochelle. The equivalent widths have been measured for 86 PMS stars with a detectable Li line (3500<T{sub eff}[K]⩽6500). Li abundance under the condition of local thermodynamic equilibrium (LTE) was derived using the conventional curve of growth method. After correction for non-LTE effects, we find that the initial Li abundance of NGC 2264 is A(Li)=3.2±0.2. From the distribution of the Li abundances, the underlying age spread of the visible PMS stars is estimated to be about 3–4 Myr and this, together with the presence of embedded populations in NGC 2264, suggests that the cluster formed on a timescale shorter than 5 Myr.

79 ASTRONOMY AND ASTROPHYSICS↗