Molecular dynamics simulation of ionic transport on molten Li–KCl interface

A molecular dynamics study is performed to determine the dynamics and transport properties of the ions on the molten interface between anode metal Li and electrolyte KCl. Radial distribution function of the ionic pair and the behavior of the mean‐square displacement (MSD) as a function of time (t) indicate that KCl and metal Li are in the molten state at 2,200 K in the canonical ensemble. The dynamics of the ionic transport are characterized by studying MSD for the centers of mass of the ions at different temperatures. Diffusion coefficient is evaluated from the linear slope of the MSD (t) function in the range of 0–500 ps. The MSD and diffusion coefficient of the Li⁺ ions are much larger than those of the Cl^? and K⁺ ions due to the difference in ionic characteristic. The transport process has been dominated by the Li⁺ ions on the molten interface and the Li⁺ ions are main charge carriers. The energy barrier of the Li⁺ ions transporting into the molten KCl is fitted to be 5.28 kcal/mol in the light of the activation model. The electrical conductivity of the Li⁺ ions transporting into the molten KCl are calculated from the Nernst–Einstein formula to be in the range of 0.2–0.3 S cm^?1. The current density resulted from the Li⁺ ions through the interface are estimated to be an order of 10⁶ A cm^?2, which may be the value corresponding to a larger concentration gradient of the Li⁺ ions. Simulated results at different temperatures show that the diffusion coefficient, conductivity and current density have increased with the temperature. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

In Situ Construction of an Ultra-Stable Conductive Composite Interface for High-Voltage All-Solid-State Lithium Metal Batteries

The garnet electrolyte presents poor wettability with Li metal, resulting in an extremely large interfacial impedance and drastic growth of Li dendrites. Herein, a novel ultra-stable conductive composite interface (CCI) consisting of Li_ySn alloy and Li₃N is constructed in situ between Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) pellet and Li metal by a conversion reaction of SnN_x with Li metal at 300 °C. The Li_ySn alloy as a continuous and robust bridge between LLZTO and Li metal can effectively reduce the LLZTO/Li interfacial resistance from 4468.0 Ω to 164.8 Ω. Meanwhile, the Li₃N as a fast Li-ion channel can efficiently transfer Li ions and give their uniform distribution at the LLZTO/Li interface. Therefore, the Li/LLZTO@CCI/Li symmetric battery stably cycles for 1200 h without short circuit, and the all-solid-state high-voltage Li/LLZTO@CCI/LiNi_0.5Co_0.2Mn_0.3O₂ battery achieves a specific capacity of 161.4 mAh g⁻¹ at 0.25 C with a capacity retention rate of 92.6 % and coulombic efficiency of 100.0 % after 200 cycles at 25 °C.     

The Li ion transport behavior in the defect graphene composite Li3N SEI: a first-principle calculation

An artificial solid electrolyte interface (SEI) of a graphene composite lithium salt can inhibit the growth of dendrites by driving the lithium deposition behavior on the surface of the lithium metal anode. The first-principle method was used to calculate the graphene/lithium nitride SEI, including the structural form and stability of intrinsic (G-Li₃N), single-vacancy defect (SVG-Li₃N), and double-vacancy defect (DVG-Li₃N) graphene heterostructure. The adsorption and migration behavior of lithium ions on the heterostructure surface and the interface were also calculated. This study showed that the modification of double-vacancy defect graphene improved the stability of the heterostructure, and the adhesion work of the composite SEI is the highest. The modification of defective graphene increases the adsorption energy of lithium atoms on the surface and interface of the heterostructure: the strongest adsorption of Li atoms on the single-vacancy defect region of the heterostructure, the opposition migration pathway of Li atoms on the surface and interface of the DVG-Li₃N heterostructure, and the decrease diffusion energy of Li atoms on the surface and interface of the DVG-Li₃N heterostructure. A composite layered SEI of graphene and Li₃N was constructed to inhibit dendritic growth by adjusting the deposition behavior of lithium atoms.     

Lithium Ion Mobility in Lithium Phosphidosilicates: Crystal Structure, 7Li, 29Si,and 31P MAS NMR Spectroscopy,and Impedance Spectroscopy of Li8SiP4 and Li2SiP2

The need to improve electrodes and Li‐ion conducting materials for rechargeable all‐solid‐state batteries has drawn enhanced attention to the investigation of lithium‐rich compounds. The study of the ternary system Li‐Si‐P revealed a series of new compounds, two of which, Li₈SiP₄ and Li₂SiP₂, are presented. Both phases represent members of a new family of Li ion conductors that display Li ion conductivity in the range from 1.15(7)×10^?6 Scm^?1 at 0 °C to 1.2(2)×10^?4 Scm^?1 at 75 °C (Li₈SiP₄) and from 6.1(7)×10^?8 Scm^?1 at 0 °C to 6(1)×10^?6 Scm^?1 at 75 °C (Li₂SiP₂), as determined by impedance measurements. Temperature‐dependent solid‐state ⁷Li NMR spectroscopy revealed low activation energies of about 36 kJ mol^?1 for Li₈SiP₄ and about 47 kJ mol^?1 for Li₂SiP₂. Both compounds were structurally characterized by X‐ray diffraction analysis (single crystal and powder methods) and by ⁷Li, ²⁹Si, and ³¹P MAS NMR spectroscopy. Both phases consist of tetrahedral SiP₄ anions and Li counterions. Li₈SiP₄ contains isolated SiP₄ units surrounded by Li atoms, while Li₂SiP₂ comprises a three‐dimensional network based on corner‐sharing SiP₄ tetrahedra, with the Li ions located in cavities and channels.     

The first compound with an unusual type of anion, [Li(SR)2]–: bis­(μ2‐aqua‐d2)tetra­kis(aqua‐d2)dilithium(I) bis­[bis­(tri‐tert‐butoxy­silanethiol­ato‐κ2O,S)lithate(I)] dihydrate‐d2

The title complex, [Li₂(D₂O)₆][Li(C₉H₂₇SSiO₃)₂]₂·2D₂O, is the first compound with an S—M bond (M = alkali metal) within an unusual type of lithate anion, [Li(SR)₂]⁻ {where R is Si[OC(CH₃)₃]₃}. There is a centre of symmetry located in the middle of the Li₂O₂ ring of the cation. All Li atoms are four‐coordinate, with LiO₄ (cations) and LiO₂S₂ (anions) cores. The singly charged [Li(SR)₂]⁻ anions are well separated from the doubly charged [Li₂(D₂O)₆]²⁺ cations; the distance between Li atoms from differently charged ions is greater than 5 Å. Both ion types are held within an extended network of O—D⋯O and O—D⋯S hydrogen bonds.     

Li15Al3Si6 (Li14.6Al3.4Si6), a compound displaying a heterographite‐like anionic framework

The title compound, lithium aluminium silicide (15/3/6), crystallizes in the hexagonal centrosymmetric space group P6₃/m. The three‐dimensional structure of this ternary compound may be depicted as two interpenetrating lattices, namely a graphite‐like Li₃Al₃Si₆ layer and a distorted diamond‐like lithium lattice. As is commonly found for LiAl alloys, the Li and Al atoms are found to share some crystallographic sites. The diamond‐like lattice is built up of Li cations, and the graphite‐like anionic layer is composed of Si, Al and Li atoms in which Si and Al are covalently bonded [Si—Al = 2.4672 (4) Å].     

In Situ Construction of an Ultra‐Stable Conductive Composite Interface for High‐Voltage All‐Solid‐State Lithium Metal Batteries

The garnet electrolyte presents poor wettability with Li metal, resulting in an extremely large interfacial impedance and drastic growth of Li dendrites. Herein, a novel ultra‐stable conductive composite interface (CCI) consisting of Li_ySn alloy and Li₃N is constructed in situ between Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) pellet and Li metal by a conversion reaction of SnN_x with Li metal at 300 °C. The Li_ySn alloy as a continuous and robust bridge between LLZTO and Li metal can effectively reduce the LLZTO/Li interfacial resistance from 4468.0 Ω to 164.8 Ω. Meanwhile, the Li₃N as a fast Li‐ion channel can efficiently transfer Li ions and give their uniform distribution at the LLZTO/Li interface. Therefore, the Li/LLZTO@CCI/Li symmetric battery stably cycles for 1200 h without short circuit, and the all‐solid‐state high‐voltage Li/LLZTO@CCI/LiNi_0.5Co_0.2Mn_0.3O₂ battery achieves a specific capacity of 161.4 mAh g^?1 at 0.25 C with a capacity retention rate of 92.6 % and coulombic efficiency of 100.0 % after 200 cycles at 25 °C.     

Electrochemical intercalation reaction of lithium into sulfides of nonlayer structure: I. Lithium intercalation in lead sulfide

The reaction mechanism of cell Li/PbS has been studied with coulombic titration, cyclic voltammetry and X-ray diffraction methods. It was found that in the first stage of discharge (0< y ≤1.5), the intercalation of lithium into lead sulfide took place. The X-ray diffraction patterns showed that the main crystalline structure of PbS remained unchanged after lithiation, and the lithium intercalated probably locates in the center of the cubic-interspace of the crystal. The intercalation free energy of Li into PbS forming LiPbS was found to be ?300.48 KJ·mol^?1 (at 25°C). The chemical diffusion coefficient of lithium in Li_yPbS (0<y≤1) was determined by electrochemical method to be about 10^?11 cm²S-1.     

Intermolecular Interactions in Li+‐glyme and Li+‐glyme–TFSA− Complexes: Relationship with Physicochemical Properties of [Li(glyme)][TFSA] Ionic Liquids

The stabilization energies (ΔE_form) calculated for the formation of the Li⁺ complexes with mono‐, di‐ tri‐ and tetra‐glyme (G1, G2, G3 and G4) at the MP2/6‐311G** level were ?61.0, ?79.5, ?95.6 and ?107.7 kcal mol^?1, respectively. The electrostatic and induction interactions are the major sources of the attraction in the complexes. Although the ΔE_form increases by the increase of the number of the O???Li contact, the ΔE_form per oxygen atom decreases. The negative charge on the oxygen atom that has contact with the Li⁺ weakens the attractive electrostatic and induction interactions of other oxygen atoms with the Li⁺. The binding energies calculated for the [Li(glyme)]⁺ complexes with TFSA^? anion (glyme=G1, G2, G3, and G4) were ?106.5, ?93.7, ?82.8, and ?70.0 kcal mol^?1, respectively. The binding energies for the complexes are significantly smaller than that for the Li⁺ with the TFSA^? anion. The binding energy decreases by the increase of the glyme chain length. The weak attraction between the [Li(glyme)]⁺ complex (glyme=G3 and G4) and TFSA^? anion is one of the causes of the fast diffusion of the [Li(glyme)]⁺ complex in the mixture of the glyme and the Li salt in spite of the large size of the [Li(glyme)]⁺ complex. The HOMO energy level of glyme in the [Li(glyme)]⁺ complex is significantly lower than that of isolated glyme, which shows that the interaction of the Li⁺ with the oxygen atoms of glyme increases the oxidative stability of the glyme.     

Chemical diffusion in intermediate phases in the lithium-tin system

The compositional variation of the chemical diffusion coefficient in the six intermediate phases LiSn, Li₇Sn₃, Li₅Sn₂, Li₁₃Sn₅, Li₇Sn₂, and Li₂₂Sn₅ of the lithium-tin system at 415°C has been measured. Among these intermediate phases, the phase Li₁₃Sn₅ has the highest chemical diffusion coefficient, varying with composition from 5.01 × 10^?5 to 7.59 × 10^?4 cm²/sec at that temperature. Combining this information with coulometric titration curves (emf versus composition), the self-diffusion coefficient of lithium has also been determined in the various intermetallic phases as a function of composition under the assumption that the tin atoms do not move appreciably compared with the lithium atoms. The lithium self-diffusion coefficient in the phase LiSn is lower than those in the more lithium-rich phases by one order of magnitude. This result is discussed in terms of the difference between the crystal structures of LiSn and the other lithium-rich phases in the lithium-tin system.     

Structural Characterisation of the Li Argyrodites Li7PS6 and Li7PSe6 and their Solid Solutions: Quantification of Site Preferences by MAS‐NMR Spectroscopy

Li₇PS₆ and Li₇PSe₆ belong to a class of new solids that exhibit high Li⁺ mobility. A series of quaternary solid solutions Li₇PS_6?xSe_x (0≤x≤6) were characterised by X‐ray crystallography and magic‐angle spinning nuclear magnetic resonance (MAS‐NMR) spectroscopy. The high‐temperature (HT) modifications were studied by single‐crystal investigations (both F$\bar 4$ 3m, Z=4, Li₇PS₆: a=9.993(1) Å, Li₇PSe₆: a=10.475(1) Å) and show the typical argyrodite structures with strongly disordered Li atoms. HT‐Li₇PS₆ and HT‐Li₇PSe₆ transform reversibly into low‐temperature (LT) modifications with ordered Li atoms. X‐ray powder diagrams show the structures of LT‐Li₇PS₆ and LT‐Li₇PSe₆ to be closely related to orthorhombic LT‐α‐Cu₇PSe₆. Single crystals of the LT modifications are not available due to multiple twinning and formation of antiphase domains. The gradual substitution of S by Se shows characteristic site preferences closely connected to the functionalities of the different types of chalcogen atoms (S, Se). High‐resolution solid‐state ³¹P NMR is a powerful method to differentiate quantitatively between the distinct (PS_4?nSe_n)^3? local environments. Their population distribution differs significantly from a statistical scenario, revealing a pronounced preference for P? S over P? Se bonding. This preference, shown for the series of LT samples, can be quantified in terms of an equilibrium constant specifying the melt reaction Se_P+S^2??S_P+Se^2?, prior to crystallisation. The ⁷⁷Se MAS‐NMR spectra reveal that the chalcogen distributions in the second and third coordination sphere of the P atoms are essentially statistical. The number of crystallographically independent Li atoms in both LT modifications was analysed by means of ⁶Li{⁷Li} cross polarisation magic angle spinning (CPMAS).     

Kristallstruktur eines Lithiumsilylamidbutanids

Crystal Structure of a Lithiumsilylamidebutanide Colorless single crystals of {Li₆[Me₂(H)Si—N—Si(H)—(CHMe₂)₂]₂[n‐C₄H₉]₄} ( 1 ) were obtained from a solution of Me₂(H)SiN(Li)Si(H)(CHMe₂)₂ and n‐C₄H₉Li in n‐hexane. The X‐ray analysis showed that the core of 1 is a distorted octahedron of lithium atoms with ten long and with two short LiÄLi distances. Four of the eight triangular Li₃ faces are capped by an n‐butyl group. The nitrogen atoms of the amide groups are situated about opposite edges of adjacent unoccupied Li₃ faces. (Si)H····Li interactions exist between the hydridic H atom of each Me₂(H)Si group and one Li atom.     

catena‐Poly­[[di­aqua­lithium(I)]‐μ‐[9H‐purine‐2,6(1H,3H)‐dionato‐O2:N7]]

In the title compound, [Li(C₅H₃N₄O₂)(H₂O)₂]_n, the coordinate geometry about the Li⁺ ion is distorted tetrahedral and the Li⁺ ion is bonded to N and O atoms of adjacent ligand mol­ecules forming an infinite polymeric chain with Li—O and Li—N bond lengths of 1.901 (5) and 2.043 (6) Å, respectively. Tetrahedral coordination at the Li⁺ ion is completed by two cis water mol­ecules [Li—O 1.985 (6) and 1.946 (6) Å]. The crystal structure is stabilized both by the polymeric structure and by a hydrogen‐bond network involving N—H?O, O—H?O and O—H?N hydrogen bonds.     

Synthesis and charge-discharge performance of Li<Subscript>5</Subscript>SiN<Subscript>3</Subscript> as a cathode material of lithium secondary batteries

Li₅SiN₃ crystals are synthesized by direct reaction between Li₃N and Si₃N₄ with the molar ratio Li₃N/Si₃N₄ of 10:1. Reaction is performed at 1073 K for 1 h under a nitrogen atmosphere of 700 Torr. The lattice constant determined by the X-ray powder diffraction method is 4.718 Å. Four broad Raman peaks are observed at 196, 286, 580, and 750 cm^?1. By analogy with LiMgN, the broad peak at 580 cm^?1 with a half width of 140 cm^?1 is attributed to homogenously random distribution of Li and Si atoms. The band gap of Li₅SiN₃ is found to be a direct gap of about 2.5 eV by optical absorption and photoacoustic spectroscopy methods. Comparison with the conventional cathode materials for lithium ion batteries, this gap value is close to d-d transition energy of Mn in LiMn₂O₄ (1.63 eV or 2.00 eV) and that of Co in LiCoO₂ (2.1 eV), suggesting that Li₅SiN₃ is a possible cathode material. The 5 × 5 mm²-sized lithium secondary battery of Li₅SiN₃ cathode/propylene carbonate + LiClO₄ electrolyte/Li anode structure shows a discharge capacity of 2.4 μAh cm^?2 for a discharge current of 1.0 μA.     

Molekül- und Kristallstruktur des 1,4-Bis[tris(tetrahydrofuran)lithium]-octaphenyltetrasilans

Molecular and Crystal Structure of 1,4-Bis[tris(tetrahydrofuran)lithium]-octaphenyltetrasilane 1,4-Dilithium-octaphenyltetrasilane prepared from octaphenyl-cyclo-tetrasilane and lithium in tetrahydrofuran (THF) [4], can be isolated from tetrahydrofuran/n-pentane as an adduct with six molecules of tetrahydrofuran per formula unit. The orange-red compound crystallizes in the triclinic space group P1 {a = 1159.6(3); b = 1268.4(2); c = 1367.8(3) pm; α = 92,23(2)° β = 113.79(2)° γ = 111.62(2)° at ?5 ± 3°C; Z = 1}. An x-ray structure determination (R_w = 0.046) shows the existence of a centrosymmetric molecule with an extended planar Li? Si₄? Li unit; either lithium atom is bound to silicon and to the oxygen atoms of three molecules of tetrahydrofuran. Characteristic bond lengths and angles are: Li? Si 271; Si? Si 241 and 243; Si? C 190 to 192 pm; Li? Si? Si 126°; Si? Si? Si 127°. ²⁹Si and ⁷Li n.m.r. measurements at low temperatures indicate the presence of three different adducts.     

Halide/sulfide composite solid-state electrolyte for Li-anode based all-solid-state batteries

Li₂ZrCl₆ (LZC) solid-state electrolytes (SSEs) have been recognized as a candidate halide SSEs for all-solid-state Li batteries (ASSLBs) with high energy density and safety due to its great compatibility with 4 V-class cathodes and low bill-of-material (BOM) cost. However, despite the benefits, the poor chemical/electrochemical stability of LZC against Li metal causes the deterioration of Li/LZC interface, which has a detrimental inhibition on Li⁺ transport in ASSLBs. Herein, we report a composite SSE combining by LZC and argyrodite buffer layer (Li₆PS₅Cl, LPSC) that prevent the unfavorable interaction between LZC and Li metal. The Li/LPSC-LZC-LPSC/Li symmetric cell stably cycles for over 1000 h at 0.3 mA/cm² (0.15 mAh/cm²) and has a high critical current density (CCD) value of 2.1 mA/cm² at 25 °C. Under high temperature (60 °C) which promotes the reaction between Li and LZC, symmetric cell fabricated with composite SSE also display stable cycling performance over 1200 h at 0.3 mAh/cm². Especially, the Li/NCM ASSLBs fabricated with composite SSE exhibit a high initial coulombic efficiency, as well as superior cycling and rate performance. This simple and efficient strategy will be instrumental in the development of halide-based high-performance ASSLBs.     

Mixed-phase WO3 Cocatalysts on Hierarchical Si-based Photocathode for Efficient Photoelectrochemical Li Extraction

Photoelectrochemical lithium (Li) extraction can be expected to provide a useful recycle of Li⁺ from waste Li-containing battery, but the process is limited by the photocathodes with poor Li⁺ absorption and low yield rate. Here, we have designed a hierarchical silicon (Si)-based photocathode with mixed-phase tungsten oxide (WO₃) cocatalysts for photoelectrochemical Li extraction under 1 sun illumination, achieving a high Li yield rate of ≈223.0 μg cm⁻² h⁻¹ and an excellent faradaic efficiency of 91.9 % at 0.0817 V versus Li^0/+ redox couple. The WO₃ cocatalysts with the mixture of amorphous and crystalline phase accelerates the Li⁺ insertion and precipitation and enriches the concentration of Li⁺ at the photocathode surface. This robust photoelectrochemical Li extraction system provides a new insight on designing green and efficient route for cyclic utilization of Li resources in the sustainable energy field.     

Water-rich molybdotellurates: Preparation and crystal structure of Li6[TeMo6O24] · 18 H2O and Li6[TeMo6O24] · Te(OH)6 · 18 H2O

Li₆[TeMo₆O₂₄] · 18 H₂O is triclinic (space group P1 , a = 1 041.7(1), b = 1 058.6(1), c = 1 070.8(1) pm, α = 61.08(1), β = 60.44(1), γ = 73.95(1)°). Single crystal X-ray structure analysis (Z = 1, 295 K, 317 parameters, 3 973 reflections, R_g = 0.0250) revealed an infinite branched chain of edge-sharing Li coordination polyhedra to be the prominent structural feature. One of the four crystallographically independent Li⁺ is coordinated octahedrally. The coordination polyhedra of the remaining Li⁺ are distorted trigonal bipyramids. Only three unique oxygen atoms (O(9), O(10), O(12)) of the centrosymmetric [TeMo₆O₂₄]^6? anion are bound to Li⁺. The further positions in the coordination spheres of the Li⁺ are occupied by water molecules. Intermolecular hydrogen bonds involve mainly oxygen atoms of the [TeMo₆O₂₄]^6? anion as nearly equivalent proton acceptors without regard to their different bonding modes to Te and Mo, respectively. Li₆[TeMo₆O₂₄] · Te(OH)₆ · 18 H₂O crystallizes monoclinically in space group P2₁/n with Z = 4, a = 994.1(3), b = 2 344.8(10), c = 1 764.9(4) pm, and β = 91.36(4)°. Single crystal structure analysis with least squares refinement of 627 parameters (5 900 reflections, 295 K) converged to R_g = 0.0324. There are six unique Li⁺ cations. The coordination polyhedra of Li(1), Li(2), Li(3), and Li(4) are linked by common edges to yield an eight membered centrosymmetric strand. The coordination polyhedra of the remaining two Li⁺ sites (Li(5), Li(6)) are connected to a dimeric unit via a common corner. All oxygen atoms of the Te(OH)₆ molecule are involved in the coordination of Li⁺. However, only three oxygen atoms (O(13), O(18), O(23)) of the [TeMo₆O₂₄]^6? anion which lacks crystallographic symmetry are involved in the coordination of Li⁺. The oxygen atoms of the anion act as proton acceptors in hydrogen bonds of predominantly medium strength. Te(OH)₆ molecules and [TeMo₆O₂₄]^6? anions connected by strong hydrogen bonds form an infinite chain.     

Synthesis,Crystal Structure and Lithium Motion of Li8SeN2 and Li8TeN2

The compounds Li₈EN₂ with E = Se, Te were obtained in form of orange microcrystalline powders from reactions of Li₂E with Li₃N. Single crystal growth of Li₈SeN₂ additionally succeeded from excess lithium. The crystal structures were refined using single‐crystal X‐ray diffraction as well as X‐ray and neutron powder diffraction data (I4₁md, No. 109, Z = 4, Se: a = 7.048(1) Å, c = 9.995(1) Å, Te: a = 7.217(1) Å, c = 10.284(1) Å). Both compounds crystallize as isotypes with an anionic substructure motif known from cubic Laves phases and lithium distributed over four crystallographic sites in the void space of the anionic framework. Neutron powder diffraction pattern recorded in the temperature range from 3 K to 300 K and X‐ray diffraction patterns using synchrotron radiation taken from 300 K to 1000 K reveal the structural stability of both compounds in the studied temperature range until decomposition. Motional processes of lithium atoms in the title compounds were revealed by temperature dependent NMR spectroscopic investigations. Those are indicated by significant changes of the ⁷Li NMR signals. Lithium motion starts for Li₈SeN₂ above 150 K whereas it is already present in Li₈TeN₂ at this temperature. Quantum mechanical calculations of NMR spectroscopic parameters reveal clearly different environments of the lithium atoms determined by the electric field gradient, which are sensitive to the anisotropy of charge distribution at the nuclear sites. With respect to an increasing coordination number according to 2 + 1, 3, 3 + 1, and 4 for Li(3), Li(4), Li(2), and Li(1), respectively, the values of the electric field gradients decrease. Different environments of lithium predicted by quantum mechanical calculations are confirmed by ⁷Li NMR frequency sweep experiments at low temperatures.     

Theoretical prediction for the structures of gas phase lithium oxide clusters: (Li2O)n (n = 1–8)

We apply genetic algorithm combining directly with density functional method to search the potential energy surface of lithium‐oxide clusters (Li₂O)_n up to n = 8. In (Li₂O)_n (n = 1–8) clusters, the planar structures are found to be global minimum up to n = 2, and the global minimum structures are all three‐dimensional at n ≥ 3. At n ≥ 4, the tetrahedral unit (TU) is found in most of the stable structures. In the TU, the central Li is bonded with four O atoms in sp³ interactions, which leads to unusual charge transformation, and the probability of the central Li participating in the bonding is higher by adaptive natural density partitioning analysis, so the central Li is in particularly low positive charge. At large cluster size, distortion of structures is viewed, which breaks the symmetry and may make energy higher. The global minimum structures of (Li₂O)₂, (Li₂O)₆, and (Li₂O)₇ clusters are the most stable magic numbers, where the first one is planar and the later both have stable structural units of tetrahedral and C_4v. © 2012 Wiley Periodicals, Inc.