7Li NMR Research Articles

Comparative NMR studies on Ca3LiRuO6 and Ca3NaRuO6

We report a comparative study of two ruthanate compounds, Ca3LiRuO6 and Ca3NaRuO6 by magnetic measurements, heat capacity and NMR. Ca3LiRuO6 is a weak ferromagnet with a magnetic ordering temperature of 115 K. The 7Li NMR linewidth of Ca3LiRuO6 displays a broad shoulder above the magnetic ordering temperature. Anomalous shoulder of this type is observed in the susceptibility data also. The origin of these phenomena is not clear but could possibly be attributed to low dimensional magnetism. A contrasting magnetic behavior is seen in Ca3NaRuO6, an antiferromagnet with a transition temperature at 87 K. The NMR study shows that the Knight shift is proportional to the magnetic susceptibility. Also, in Ca3NaRuO6, the Knight shift and the linewidth of the spectra change differently compared to Ca3LiRuO6. The heat capacity of both compounds show a λ-type anomaly at respective magnetic transition temperatures. However, in both the systems the entropy change (S) is much less than that of an ordered S = 3/2 system.

Ab Initio Molecular Dynamics Simulations and GIPAW NMR Calculations of a Lithium Borate Glass Melt.

The atomic structure of a molten 0.3Li2O-0.7B2O3 glass at 1250 K was investigated using ab initio molecular dynamics (AIMD) simulations. The gauge including projector augmented wave (GIPAW) method was then employed for computing the chemical shift and quadrupolar coupling constant of (11)B, (17)O, and (7)Li from 764 AIMD derived structures. The chemical shift and quadrupolar coupling constant distributions were directly estimated from the dynamical structure of the molten glass. (11)B NMR parameters of well-known structural units such as the three-coordinated ring, nonring, and four-coordinated tetrahedron were found to be in good agreement with the experimental results. In this study, more detailed classification of B units was presented based on the number of O species bonded to the B atoms. This highlights the limitations of (11)B NMR sensitivity for resolving (11)B local environment using the experimentally obtained spectra only. The (17)O NMR parameter distributions can theoretically resolve the bridging and nonbridging O atoms with different structural units such as nonring, single boroxol ring, and double boroxol ring. Slight but clear differences in the number of bridging O atoms surrounding Li that have not been reported experimentally were observed in the theoretically obtained (7)Li NMR parameters.

Substitution of Lithium for Magnesium, Zinc, and Aluminum in Li15 Si4 : Crystal Structures, Thermodynamic Properties, as well as (6) Li and (7) Li NMR Spectroscopy of Li15 Si4 and Li15-x Mx Si4 (M=Mg, Zn, and Al).

An investigation into the substitution effects in Li15 Si4 , which is discussed as metastable phase that forms during electrochemical charging and discharging cycles in silicon anode materials, is presented. The novel partial substitution of lithium by magnesium and zinc is reported and the results are compared to those obtained for aluminum substitution. The new lithium silicides Li14 MgSi4 (1) and Li14.05 Zn0.95 Si4 (2) were synthesized by high-temperature reactions and their crystal structures were determined from single-crystal data. The magnetic properties and thermodynamic stabilities were investigated and compared with those of Li14.25 Al0.75 Si4 (3). The substitution of a small amount of Li in metastable Li15 Si4 for more electron-rich metals, such as Mg, Zn, or Al, leads to a vast increase in the thermodynamic stability of the resulting ternary compounds. The (6,7) Li NMR chemical shift and spin relaxation time T1 -NMR spectroscopy behavior at low temperatures indicate an increasing contribution of the conduction electrons to these NMR spectroscopy parameters in the series for 1-3. However, the increasing thermal stability of the new ternary phases is accompanied by a decrease in Li diffusivity, with 2 exhibiting the lowest activation energy for Li mobility with values of 56, 60, and 62 kJ mol(-1) for 2, Li14.25 Al0.75 Si14 , and 1, respectively. The influence of the metastable property of Li15 Si4 on NMR spectroscopy experiments is highlighted.

Syntheses and structures of two new lithium-heptamolybdates

The synthesis, crystal structures, IR, UV–vis, 7Li NMR spectra, electrochemical investigations, and conductivity studies of two new lithium-heptamolybdates, (NH4)4[Li2(H2O)7][Mo7O24]·H2O (1) and (NH4)3[Li3(H2O)4(μ6-Mo7O24)]·2H2O (2), are reported. In 1 the (NH4)+ and [Li2(H2O)7]2+, cations are charge balanced by the heptamolybdate anion. In 2, the [Mo7O24]6− anion is coordinated to three unique Li+ ions via a μ6-hexadentate-binding mode resulting in the formation of a two-dimensional (2-D) [Li3(H2O)4(μ6-Mo7O24)]3− anionic complex, charge neutralized by three (NH4)+ ions. The cations, anions, and the lattice water molecules in 1 and 2 are linked by weak H-bonding interactions.

In Situ NMR Insights into the Electrochemical Reaction of Cu3P Electrodes in Lithium Batteries

This study reports a multinuclei in situ (real-time) NMR spectroscopic characterization of the electrochemical reactions of a negative Cu3P electrode toward lithium. Taking advantage of the different nuclear spin characteristics, we have obtained real-time 31P and 7Li NMR data for a comprehensive understanding of the electrochemical mechanism during the discharge and charge processes of a lithium battery. The large NMR chemical shift span of 31P facilitates the observation of the chemical evolutions of different lithiated and delithiated LixCu3–xP phases, whereas the quadrupolar line features in 7Li enable identification of asymmetric Li sites. These combined NMR data offer an unambiguous identification of four distinct LixCu3–xP phases, Cu3P, Li0.2Cu2.8P, Li2CuP, and Li3P, and the characterization of their involvement in the electrochemical reactions. The NMR data led us to propose a delithiation process involving the intercalation of metallic Cu0 atomic aggregates into the Li2CuP structure to form a Cu0...

Crystal Structure of Garnet-Related Li-Ion Conductor Li7-3x Ga x La3Zr2O12: Fast Li-Ion Conduction Caused by a Different Cubic Modification?

Li-oxide garnets such as Li7La3Zr2O12 (LLZO) are among the most promising candidates for solid-state electrolytes to be used in next-generation Li-ion batteries. The garnet-structured cubic modification of LLZO, showing space group Ia-3d, has to be stabilized with supervalent cations. LLZO stabilized with Ga3+ shows superior properties compared to LLZO stabilized with similar cations; however, the reason for this behavior is still unknown. In this study, a comprehensive structural characterization of Ga-stabilized LLZO is performed by means of single-crystal X-ray diffraction. Coarse-grained samples with crystal sizes of several hundred micrometers are obtained by solid-state reaction. Single-crystal X-ray diffraction results show that Li7–3xGaxLa3Zr2O12 with x > 0.07 crystallizes in the acentric cubic space group I-43d. This is the first definite record of this cubic modification for LLZO materials and might explain the superior electrochemical performance of Ga-stabilized LLZO compared to its Al-stabilized counterpart. The phase transition seems to be caused by the site preference of Ga3+. 7Li NMR spectroscopy indicates an additional Li-ion diffusion process for LLZO with space group I-43d compared to space group Ia-3d. Despite all efforts undertaken to reveal structure–property relationships for this class of materials, this study highlights the potential for new discoveries.

Comparative structural analysis of LiMPO4 and Li2MPO4F (M = Mn, Fe, Co, Ni) according to XRD, IR, and NMR spectroscopy data

A comparative structural study of LiMPO4 (M = Mn, Fe, Co, Ni) orthophosphates and Li2MPO4F (M = Co, Ni) fluorophosphates obtained by mechanochemically assisted solid-state synthesis is performed using powder XRD, IR, and NMR spectroscopy methods. It is shown that all compounds crystallize in the orthorhombic symmetry (space group Pnma). Lattice parameters decrease on passing from Mn to Ni, which is due to the decrease in the ionic radius of the d metal. According to the IR spectroscopy data, in this series an increase in the covalency of the P–O bond is observed along with a decrease in the covalency of the M–O bond. On passing to fluorophosphates, the symmetry of PO4 tetrahedra increases. 6Li and 31P NMR spectra of all compounds are characterized by the dependence of the contact shift on the nature of metal M and the degree of distortion of the MO6 coordination polyhedron. 6Li MAS NMR line width is noticeably affected by the concentration of structural defects. Unlike orthophosphates with equivalent lithium ions, fluorophosphates contain lithium ions in three different positions.

Reprint of Structural characterization of a tetrametallic diamine-bis(phenolate) complex of lithium and synthesis of a related bismuth complex

A novel lithium complex was prepared from the reaction of 1,4-bis(2-hydroxy-3,5-di-tert-butyl-benzyl)imidazolidine H2[O2N2]BuBuIm (L1H2) with n-butyllithium to provide the corresponding tetralithium amine-bis(phenolate) complex {Li2[L1]}2·4THF, 1. Variable temperature 7Li NMR revealed that this complex is labile in solution, dissociating at elevated temperatures to afford two dilithium entities. Additionally, 7Li MAS NMR was performed on 1 to provide information regarding the lithium coordination environment in the bulk solid-state. The reactivity of 1 was assessed in the ring-expansion polymerization of ε-caprolactone (ε-CL), which was first order in ε-CL with an activation energy of 50.9kJmol−1. Reaction of 1 and a related Li complex (formed in situ) with BiCl3 afforded hydrolytically unstable bismuth phenolate species, as evidenced by the isolation and structural characterization of [Bi4(Cl)3(μ-Cl)(μ-O)(O)2{[O2N2]BuBuPip}2], 2, where [O2N2]BuBuPip is the homopiperazine-containing analog of L1.

Diffusion-induced 7Li NMR spin-lattice relaxation of fully lithiated, mixed-conducting Li7Ti5O12

Li4Ti5O12 (LTO) belongs to one of the most promising anode materials for lithium-ion batteries. Its superior cycling performance and negligible aging make it a potential candidate to be used in, e.g., stationary applications. Besides this application-oriented interest it serves as an excellent model system to study Li ion transport in a 3D mixed conducting host crystallizing with spinel structure. Whereas Li ion diffusion in Li4Ti5O12 was the subject of several studies that appeared over the past years; Li ion transport in mixed conducting Li7Ti5O12 crystallizing with rock-salt type structure is, however, much less frequently investigated. Li7Ti5O12 is the compound that is formed after an LTO-type battery has been fully charged. In the present study we used spin-lock NMR relaxometry to quantify Li ion diffusion in terms of jump rates, activation energies and microscopic Li ion self-diffusion coefficients. Extending the measurements to higher temperatures enabled us to record the diffusion induced rate maxima from which Li+ self-diffusion coefficients were obtained directly. Compared to the non-lithiated source material Li4Ti5O12, showing poor Li ion diffusivity, Li ion diffusivity in Li7Ti5O12 is clearly enhanced but by far as high as recently reported for spinel-type Li4+xTi5O12, with x being significantly smaller than 1. Obviously, the small number of vacant 16c sites in Li7Ti5O12 as well as repulsive the 8a–16c interactions are responsible for the low Li ion diffusivity found.

7Li NMR studies of lithium ion dynamics in polymer-derived silicon oxycarbide ceramics

7Li NMR spin–lattice relaxation, line-shape, and stimulated-echo analyses are performed to investigate lithium ionic motion in a polymer-derived silicon oxycarbide (SiOC) ceramic. In particular, we compare microscopic jump dynamics in lithiated and delithiated compounds. We find that the large variety of lithium environments in the studied SiOC ceramic results in broad distributions of correlation times for the jump motion of the lithium ions, but the experimental results yield no evidence that clearly distinguishable lithium dynamics can be attributed to various electrochemically active lithium sites in different regions of structurally heterogeneous carbon-rich materials. Moreover, we observe that the lithium ionic jumps are, on average, faster in the lithiated than in the delithiated compound at ambient temperatures. Specifically, the mean logarithmic correlation times amount to τm=2⋅10-4s and τm=1⋅10-2s for the former and latter samples at 300K, respectively. On the other hand, the temperature dependence of lithium jumps is higher for lithiated than for delithiated SiOC so that the difference in the ionic mobilities is reduced upon cooling. Finally, we show that the prepared lithiated and delithiated samples undergo irreversible changes when heating to 400K. Specifically, when subject to thermal treatment, 7Li spin–lattice relaxation becomes slower for one lithium fraction, while it remains unaffected for another lithium fraction.

Natural abundance 17O, 6Li NMR and molecular modeling studies of the solvation structures of lithium bis(fluorosulfonyl)imide/1,2-dimethoxyethane liquid electrolytes

Natural abundance 17O and 6Li NMR experiments, quantum chemistry and molecular dynamics studies were employed to investigate the solvation structures of Li+ at various concentrations of LiFSI in DME electrolytes. It was found that the chemical shifts of both 17O and 6Li changed with the concentration of LiFSI, indicating the changes of solvation structures with concentration. For the quantum chemistry calculations, the coordinated cluster LiFSI(DME)2 forms at first, and its relative ratio increases with increasing LiFSI concentration to 1 M. Then the solvation structure LiFSI(DME) become the dominant component. As a result, the coordination of forming contact ion pairs between Li+ and FSI− ion increases, but the association between Li+ and DME molecule decreases. Furthermore, at LiFSI concentration of 4 M the solvation structures associated with Li+(FSI−)2(DME), Li+2(FSI−)(DME)4 and (LiFSI)2(DME)3 become the dominant components. For the molecular dynamics simulation, with increasing concentration, the association between DME and Li+ decreases, and the coordinated number of FSI− increases, which is in perfect accord with the DFT results.

Aromatic Dicupra[10]annulenes.

Metal-containing aromatic systems (metalla-aromatics) are unique and important both experimentally and theoretically. Among metalla-aromatics, six-membered metallabenzenes and metallabenzynes have attracted much attention in recent years. However, reports on their superior homologues are rare. In this work, the first series of aromatic dicupra[10]annulenes were isolated from the reaction of dilithio reagents and copper salts. Single-crystal X-ray structural analysis revealed dicupra[10]annulenes with averaged bond lengths. (7)Li NMR spectra and theoretical calculations revealed considerable aromatic character. XPS data suggested that the oxidation state of Cu atom in dicupra[10]annulenes was more likely to be Cu(I), indicating that the dilithio moieties in dicupra[10]annulenes participated as noninnocent ligands. This work demonstrates a novel approach to construct macrocyclic metalla-aromatics.

High-pressure/high-temperature synthesis and characterization of the first palladium or platinum containing lithium transition-metal sulfides Li2M3S4 (M=Pd, Pt)

The new lithium transition-metal sulfides Li2M3S4 (M=Pd, Pt) were obtained via multianvil high-pressure/high-temperature syntheses at 8GPa and 1150°C starting from a stoichiometric mixture of lithium nitride, sulfur, and palladium or platinum. Single crystal structure analyses indicated the space group P21/c (no. 14) with the following lattice parameters and refinement results: a=492.9(1), b=1005.9(2), c=614.9(2)pm, β=110.9 (1)°, R1=0.0165, wR2=0.0308 (all data) for Li2Pd3S4 and a=498.2(1), b=1005.5(2), c=613.0(2)pm, β=110.8(1)°, R1=0.0215, wR2=0.0450 (all data) for Li2Pt3S4. The crystal structures are built up from two distinct Pd/Pt sites, one of which is a special position (0,0,0), two sulfur sites, and one lithium site. The atoms Pd2/Pt2 form isolated square planar PdS4/PtS4 units, whereas the Pd1/Pt1 atoms form pairs of square planar PdS4/PtS4 units, which are connected via a common edge. These two structural motives built up a three-dimensional network structure by linking through common corners. The lithium atoms are positioned inside of the so formed channels. Li2M3S4 (M=Pd, Pt) are isostructural to the minerals jaguéite, Cu2Pd3Se4 and chrisstanleyite, Ag2Pd3Se4, which are up to now the only representatives of this structure type. Both compounds were studied with respect to their magnetic properties and can be classified as Pauli paramagnetic or diamagnetic. Regarding the possibility of lithium mobility inside the channels, of the structure, solid state 7Li NMR and high-temperature single crystal investigations revealed localization of the lithium atoms on their crystallographic sites.

Li+ ion transport in ionic liquid-based electrolytes and the influence of sulfonate-based zwitterion additives

The influence of sulfonate-based zwitterion (ZI) additives on the thermodynamic properties, ion transport properties and electrochemical properties of ionic liquid/Li-TFSI mixtures was studied by combining a number of experimental methods, namely DSC, conductivity measurements, viscosity measurements, 7Li NMR spectroscopy, pulsed field gradient NMR spectroscopy (PFG-NMR), Raman spectroscopy and cyclic voltammetry. We find that the addition of ZI leads to a suppression of crystallization processes in the ternary mixtures. The ion transport properties were analysed in a modified Walden plot with a newly defined reference line. The comparison of experimental data with the reference line points to simple liquid behaviour at high temperatures around 100°C and to a dynamic decoupling of faster ionic species from slower ionic species at lower temperatures. Thus, the addition of ZI increases the amount of decoupling in IL/Li salt mixtures. This interpretation is confirmed by the results of the PFG-NMR measurements, which indicate the existence of faster TFSI− anions and slower Li+/ZI complexes in the ternary mixtures. Raman spectra reveal strong changes in the coordination environment of the TFSI− anion upon addition of the ZIs. The cyclic voltammograms point to a cathodic shift of the Li+ reduction potential caused by the strong binding between Li+ ions and ZI.

Ge2]4− Dumbbells with Very Short Ge−Ge Distances in the Zintl Phase Li3NaGe2: A Solid‐State Equivalent to Molecular O2

AbstractThe novel ternary Zintl phase Li3NaGe2 comprises alkali‐metal cations and [Ge2]4− dumbbells. The diatomic [Ge2]4− unit is characterized by the shortest Ge−Ge distance (2.390(1) Å) ever observed in a Zintl phase and thus represents the first Ge=Ge double bond under such conditions, as also suggested by the (8−N) rule. Raman measurements support these findings. The multiple‐bond character is confirmed by electronic‐structure calculations, and an upfield 6Li NMR shift of −10.0 ppm, which was assigned to the Li cations surrounded by the π systems of three Ge dumbbells, further underlines this interpretation. For the unperturbed, ligand‐free dumbbell in Li3NaGe2, the π‐ bonding py and pz orbitals are degenerate as in molecular oxygen, which has singly occupied orbitals. The partially filled π‐type bands of the neat solid Li3NaGe2 cross the Fermi level, resulting in metallic properties. Li3NaGe2 was synthesized from the elements as well as from binary reactants and subsequently characterized crystallographically.

Ge2](4-) Dumbbells with Very Short Ge-Ge Distances in the Zintl Phase Li3NaGe2: A Solid-State Equivalent to Molecular O2.

The novel ternary Zintl phase Li3NaGe2 comprises alkali-metal cations and [Ge2](4-) dumbbells. The diatomic [Ge2](4-) unit is characterized by the shortest Ge-Ge distance (2.390(1) Å) ever observed in a Zintl phase and thus represents the first Ge=Ge double bond under such conditions, as also suggested by the (8-N) rule. Raman measurements support these findings. The multiple-bond character is confirmed by electronic-structure calculations, and an upfield (6)Li NMR shift of -10.0 ppm, which was assigned to the Li cations surrounded by the π systems of three Ge dumbbells, further underlines this interpretation. For the unperturbed, ligand-free dumbbell in Li3NaGe2, the π- bonding py and pz orbitals are degenerate as in molecular oxygen, which has singly occupied orbitals. The partially filled π-type bands of the neat solid Li3NaGe2 cross the Fermi level, resulting in metallic properties. Li3NaGe2 was synthesized from the elements as well as from binary reactants and subsequently characterized crystallographically.

High grain boundary density Li4Ti5O12/anatase-TiO2 nanocomposites as anode material for Li-ion batteries

Li4Ti5O12/TiO2 nanocomposites are synthesized by a sol-gel method. The size of Li4Ti5O12 and TiO2 particles is of 4–5 and 7–10nm, respectively. The obtained materials are characterized by XRD, SEM, HRTEM and BET. Ion mobility of the composites and their performance as anode materials for lithium-ion batteries are studied. According to the conductivity and 7Li NMR data, Li+ mobility is much higher in the Li4Ti5O12/TiO2 nanocomposites as compared with that in pure Li4Ti5O12. For Li4Ti5O12/TiO2 nanocomposites, marked changes in the charge–discharge curves are observed; charge–discharge rate and effective capacity at a high cycling rate are shown to increase. During the first cycle, charge capacity of these materials surpasses the theoretical capacity of Li4Ti5O12. However, this parameter decreases sharply with cycling, whereas the discharge capacity remains almost unchanged. This phenomenon is attributed to the solid electrolyte interphase formation due to a partial electrolyte reduction on the Li4Ti5O12/TiO2 composite surface.

Anion Reorientations and Cation Diffusion in LiCB11H12 and NaCB11H12: 1H, 7Li, and 23Na NMR Studies

To study the dynamical properties of the monocarba-closo-dodecaborates LiCB11H12 and NaCB11H12 showing the exceptionally high ionic conductivities in the high-temperature disordered phases, we have measured the temperature dependences of the 1H, 7Li, and 23Na NMR spectra and spin–lattice relaxation rates in these compounds below and above the phase transition points. It has been found that for both compounds the transition from the low-T ordered to the high-T disordered phase (near 384 and 376 K for LiCB11H12 and NaCB11H12, respectively) is accompanied by a nearly 3 orders of magnitude increase in the reorientational jump rate of [CB11H12]− anions. The results of our 7Li and 23Na NMR measurements indicate that the phase transitions from the low-T to the high-T phases of both LiCB11H12 and NaCB11H12 are also accompanied by a strong acceleration of translational diffusion of cations (Li+ or Na+). In the high-T phases of LiCB11H12 and NaCB11H12, the cation diffusion is characterized by low activation energie...

Evaluation of the Stability of Trimethyl Phosphate as a Li–O2 Battery Electrolyte via Multinuclear Solid-State NMR

Solid-state 17O NMR was used to compare the stability of two potential Li–O2 electrolytes—tetraethylene glycol dimethyl ether (TEGDME) and trimethyl phosphate (TMP). The TEGDME electrolyte demonstrated superior stability to the TMP electrolyte. Li2O2 and evidence of electrolyte breakdown was observed in the TEGDME cell, whereas only electrolyte breakdown products were discovered within the TMP cell. Potential decomposition pathways of TMP are proposed here that account for the formation of the discharge species observed in the 17O, 7Li, 1H, and 31P solid-state NMR of the cycled cathodes.

Solid-State and Solution Structures of Glycinimine-Derived Lithium Enolates.

A combination of crystallographic, spectroscopic, and computational studies was applied to study the structures of lithium enolates derived from glycinimines of benzophenone and (+)-camphor. The solvents examined included toluene and toluene containing various concentrations of tetrahydrofuran, N,N,N',N'-tetramethylethylenediamine (TMEDA), (R,R)-N,N,N',N'-tetramethylcyclohexanediamine [(R,R)-TMCDA], and (S,S)-N,N,N',N'-tetramethylcyclohexanediamine [(S,S)-TMCDA]. Crystal structures show chelated monomers, symmetric disolvated dimers, S4-symmetric tetramers, and both S6- and D3d-symmetric hexamers. (6)Li NMR spectroscopic studies in conjunction with the method of continuous variations show how these species distribute in solution. Density functional theory computations offer insights into experimentally elusive details.