Li NMR Studies Research Articles

Effects of Li Confined Motion on NMR Quadrupolar Interactions: A Combined 7 Li NMR and DFT-MD Study of LiR2 (PO4 )3 (R=Ti or Zr) Phases.

Ab initio molecular dynamics (MD) simulations and NMR GIPAW (gauge including projector augmented wave) calculations have been used to analyze the coordination and mobility of Li ions in LiTi2(PO4)3 (rhombohedral), LiZr2(PO4)3 (triclinic), and LiZr2(PO4)3 (rhombohedral) phases. Significant discrepancies are observed between static calculations of 7Li quadrupolar parameters and experimental values. The dynamical origin of this disagreement is demonstrated by incorporating in the calculations thermal vibrations and local motion of atoms with MD simulations. For LiTi2(PO4)3, the quadrupolar constant associated with Li ions grows with temperature because the local symmetry of the system decreases, whereas for the Zr phases, the quadrupolar constant decreases because thermal vibrations reduce the anisotropy of the interaction. Finally, for both Zr phases, MD yields Li distributions that compare well with disorder reported from diffraction studies.

Classical Spin Nematic Transition in LiGa_{0.95}In_{0.05}Cr_{4}O_{8}.

We present the results of a combined ^{7}Li-NMR and diffraction study on LiGa_{0.95}In_{0.05}Cr_{4}O_{8}, a member of the LiGa_{1-x}In_{x}Cr_{4}O_{8} "breathing" pyrochlore family. Via specific heat and NMR measurements, we find that the complex sequence of first-order transitions observed for LiGaCr_{4}O_{8} is replaced by a single second-order transition at T_{f}=11 K. Neutron and x-ray diffraction rule out both structural symmetry lowering and magnetic long-range order as the origin of this transition. Instead, reverse MonteCarlo fitting of the magnetic diffuse scattering indicates that the low-temperature phase may be described as a collinear spin nematic state, characterized by a quadrupolar order parameter. This state also shows signs of short-range order between collinear spin arrangements on tetrahedra, revealed by mapping the reverse MonteCarlo spin configurations onto a three-state color model.

Oxygen Containing Carbon Materials for High Capacity and Fast Chargeable Anode Materials of Lithium Ion Batteries

The lithium-ion battery is the most promising energy storage devices for variety of applications from portable electronics to electric vehicles because of its high energy density, power density and cycle life. However, the upcoming boom for artificial intelligence (AI) assisted transportations, Internet of Things (IoT) or potential wireless financial technologies may require batteries with much higher energy density and fast chargeable capability. Silicon and silicon monoxide have been extensive investigated for high capacity anode for more than 10 years. However, they are still hard to be used in real practice because of large volumetric expansion, poor cycle life, and bad rate capability. On the other hand, graphite is the most popular commercialized anode material for Li-ion battery because of its excellent coulombic efficiency, long cycle life, low cost and ease of processing. However, the limited theoretical capacity (372 mAh/g) and small interlayer spaces (0.335 nm) made it difficult to be used in the application of Li-ion batteries with higher energy density and fast chargeable Li-ion batteries (Fig.1a). In this study, we have introduced a novel Graphene-Like-Graphite (GLG) anode material to be used in Li-ion batteries with higher capacity and good rate capability. According to the Li-NMR study, lithium ions can intercalate into graphene layers with oxygen at 0-1.2V (vs Li) with non-stage phenomenon and delivered a capacity more than 372mAh/g. Meanwhile, at a higher potential range from 1.2 to 2V (vs Li), lithium ions continuous react with oxygen containing functional groups reversibly on the basal plane of each graphene layer. As a result, the GLG could have an initial discharge capacity up to 608mAh/g which is much larger than conventional graphite (372mAh/g). It was investigated that the higher oxygen content offers a higher reversible capacity over 1.2V (vs Li) discharge. Atom resolution STEM is also carried out for the characterization of single layer graphene of the GLG. It was learned that the GLG graphene layer has pore structure with the size less than 2nm, moreover the oxygen containing functional groups were attached on both basal plane and pores` s edge. The GLG was also characterized with NCM111 cathode for full-cell rate capability and cyclability. The cell charged to 60% of the capacity up to 6C (10min) charge with 103wh/kg cell design, while have good cycle ability. XPS, HAXPES, C-NMR were also used for the characterization of the GLG materials. Finally, a structure model was proposed for the next generation high rate, high capacity carbon based anode materials. Figure 1

Ab initio structure search and in situ 7Li NMR studies of discharge products in the Li-S battery system.

The high theoretical gravimetric capacity of the Li–S battery system makes it an attractive candidate for numerous energy storage applications. In practice, cell performance is plagued by low practical capacity and poor cycling. In an effort to explore the mechanism of the discharge with the goal of better understanding performance, we examine the Li–S phase diagram using computational techniques and complement this with an in situ 7Li NMR study of the cell during discharge. Both the computational and experimental studies are consistent with the suggestion that the only solid product formed in the cell is Li2S, formed soon after cell discharge is initiated. In situ NMR spectroscopy also allows the direct observation of soluble Li+-species during cell discharge; species that are known to be highly detrimental to capacity retention. We suggest that during the first discharge plateau, S is reduced to soluble polysulfide species concurrently with the formation of a solid component (Li2S) which forms near the beginning of the first plateau, in the cell configuration studied here. The NMR data suggest that the second plateau is defined by the reduction of the residual soluble species to solid product (Li2S). A ternary diagram is presented to rationalize the phases observed with NMR during the discharge pathway and provide thermodynamic underpinnings for the shape of the discharge profile as a function of cell composition.

Contrasting Reactivity of Mono- versus Bis-2,2,6,6-tetramethylpiperidide Lithium Aluminates Towards Polydentate Lewis Bases: Co-Complexation Versus Deprotonation

Two closely related lithium alkylaluminium amides LiAl(TMP)2iBu2 and LiAl(TMP)iBu3 (TMP: 2,2,6,6-tetramethylpiperidide) have been compared in their reactivity towards six polydentate Lewis bases containing either N or O donor atoms or a mixed N,O donor set. Seven of the twelve potential organometallic products of these reactions, which were carried out in hexane solution, have been crystallographically characterised. Three of these structures, [Li(μ-Me2NCH2CHCH2CH2CHO)(μ-TMP)Al(iBu)2], [Li(μ-Me2NCH2CH2OCH2)(μ-TMP)Al(iBu)2], and [Li(μ-Me2NCH2CH2OCHCH2NMe2)(μ-TMP)Al(iBu)2] reveal that the bis-amide LiAl(TMP)2iBu2 deprotonates (aluminates) the multifunctional Lewis base selectively at the carbon atom adjacent to oxygen with the anion generated captured by the residue of the base. In contrast, the mono-amide LiAl(TMP)iBu3 in general fails to deprotonate the Lewis bases but instead forms co-complexes with them as evidenced by the molecular structures of [Me2NCH2CHCH2CH2CH2O·Li(μ-iBu)(μ-TMP)Al(iBu)2], [Me2NCH2CH2OMe·Li(μ-iBu)(μ-TMP)Al(iBu)2], and [MeOCH2CH2OMe·Li(μ-iBu)(μ-TMP)Al(iBu)2]. Providing an exception to this pattern, the mono-amide reagent deprotonates chiral R,R,-N,N,N′,N′-tetramethylcyclohexanediamine to afford [Li(μ-CH2NMeC6H10NMe2)2Al(iBu)2], the final complex to be crystallographically characterised. All new products have been spectroscopically characterised through 1H, 7 Li, and 13C NMR studies. Reaction mixtures have also been quenched with D2O and analysed by 2D NMR spectroscopy to ascertain the full metallation versus co-complexation picture taking place in solution.

Analysis of inner-pore structure of carbon materials using Li and Xe NMR

Closed pores in non-graphitazable carbon (hard carbon) are the reason for some unique properties for lithium intercalation. Our group investigated intercalated Li in hard carbon, which is used for the anode active material of lithium ion batteries for electric vehicles, using solid state 7Li NMR. The correlation between deposition of lithium clusters in the pores and the state of charge were elucidated. The growth of the porous structure of hard carbon was also investigated using 129Xe NMR porosimetry. Xe NMR could evaluate pores in hard carbon that were hard to investigate by adsorption isotherm measurement. A Li NMR study for a ternary graphite intercalation compound consisting of alkylamine and Li is also presented.

7Li NMR Studies on Complexation Reactions of Lithium Ion with Cryptand C211 in Ionic Liquids: Comparison with Corresponding Reactions in Nonaqueous Solvents

(7)Li NMR spectra of DEME-TFSA [DEME=N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium; TFSA=bis(trifluoromethanesulfonyl)amide], EMI-TFSA (EMI=1-ethyl-3-methylimidazolium), MPP-TFSA (MPP = N-methyl-N-propylpyridinium), DEME-PFSA [PFSA=bis(pentafluoroethanesulfonyl)amide], and DEME-HFSA [HFSA=bis(heptafluoropropanesulfonyl)amide] ionic liquid (IL) solutions containing LiX (X=TFSA, PFSA, or HFSA) and C211 (4,7,13,18-tetraoxa-1,10-diazabicyclo[8.5.5]eicosane) were measured at various temperatures. As a result, it was found that the uncomplexed Li(I) species existing as [Li(X)(2)](-) in the present ILs exchange with the complexed Li(I) ([Li·C211](+)) and that the exchange reactions proceed through the bimolecular mechanism, [Li·C211](+) + [*Li(X)(2)](-)=[*Li·C211](+) + [Li(X)(2)](-). Kinetic parameters [k(s)/(kg m(-1) s(-1)) at 25 °C, ΔH(++)/(kJ mol(-1)), ΔS(++)/(J K(-1) mol(-1))] are as follows: 5.57×10(-2), 69.8 ± 0.4, and -34.9 ± 1.0 for the DEME-TFSA system; 5.77×10(-2), 70.6 ± 0.2, and -31.9 ± 0.6 for the EMI-TFSA system, 6.13×10(-2), 69.0 ± 0.3, and -36.7 ± 0.7 for the MPP-TFSA system; 1.35 × 10(-1), 65.2 ± 0.5, and -43.1 ± 1.4 for the DEME-PFSA system; 1.14×10(-1), 64.4 ± 0.3, and -47.1 ± 0.6 for the DEME-HFSA system. To compare these kinetic data with those in conventional nonaqueous solvents, the exchange reactions of Li(I) between [Li·C211](+) and solvated Li(I) in N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) were also examined. These Li(I) exchange reactions were found to be independent of the concentrations of the solvated Li(I) and hence proposed to proceed through the dissociative mechanism. Kinetic parameters [k(s)/s(-1) at 25 °C, ΔH(++)/(kJ mol(-1)), ΔS(++)/(J K(-1) mol(-1))] are as follows: 1.10 × 10(-2), 68.9 ± 0.2, and -51.3 ± 0.4 for the DMF system; 1.13×10(-2), 76.3 ± 0.3, and -26.3 ± 0.8 for the DMSO system. The differences in reactivities between ILs and nonaqueous solvents were proposed to be attributed to those in the chemical forms of the uncomplexed Li(I) species, i.e., the negatively charged species ([Li(X)(2)](-)) in ILs, and the positively charged ones ([Li(solvent)(n)](+)) in nonaqueous solvents.

Analysis of inner-pore structure of carbon materials using Li and Xe NMR

Closed pores in non-graphitazable carbon (hard carbon) are the reason for some unique properties for lithium intercalation. Our group investigated intercalated Li in hard carbon, which is used for the anode active material of lithium ion batteries for electric vehicles, using solid state 7Li NMR. The correlation between deposition of lithium clusters in the pores and the state of charge were elucidated. The growth of the porous structure of hard carbon was also investigated using 129Xe NMR porosimetry. Xe NMR could evaluate pores in hard carbon that were hard to investigate by adsorption isotherm measurement. A Li NMR study for a ternary graphite intercalation compound consisting of alkylamine and Li is also presented.

Ligand Exchange Processes on Solvated Lithium Cations. VI. Determination of Coordination Numbers by Ligand Substitution and 7Li NMR

Graphical Abstract Ligand Exchange Processes on Solvated Lithium Cations. VI. Determination of Coordination Numbers by Ligand Substitution and 7 Li NMR On the basis of 7 Li NMR studies the coordination mode of phenantroline (phen) and bipyridine (bipy) to Li + ions was found to be [Li(phen) 2 ] + and [Li(bipy) 2 ] + in the weakly coordinating solvent nitromethane. A large chemical shift of the 7 Li signal indicated a strong interaction between the ligand and the metal center. The related sp 2 -hybridized N-donor ligand 2,2´-bis[(4S)-4-benzyl-2- oxazoline] (biox) showed a negligible effect on the 7 Li shift, suggesting that almost no interaction occurs between the Li + center and biox as compared to Li + and the solvent γ -butyrolactone. Corresponding DFT (RB3LYP/LANL2DZp) calculations have clearly indicated that the poor coordination of biox is not caused by steric effects but rather by the electronic nature of the heterocyclic biox system.

Synthesis of Li4V(PO4)2F2 and 6,7Li NMR studies of its lithium ion dynamics

A single phase, well-crystallized Li4V(PO4)2F2/carbon nanocomposite has been prepared by an optimized solid-state route via oxidation of Li5V(PO4)2F2. The Li4V(PO4)2F2 composition exhibits lattice parameters close to those of the oxidized parent (a = 6.898 A, b = 10.673 A, c = 9.977 A; β = 87.84°; V = 734.0 A3). 1D 6Li solid-state magic-angle spinning nuclear magnetic resonance (MAS NMR) studies identified which of the six lithium ions are removed from the lattice of the parent Li5V(PO4)2F2. The results are in perfect accord with previous NMR-based predictions of which sites would be the most mobile and thereby most easily extracted upon cycling. Variable-temperature NMR studies and 2D exchange spectroscopy (EXSY) are used to probe the Li ion dynamics in Li4V(PO4)2F2. Importantly, our studies show that upon delithiation, the ion mobility was found to increase significantly vis a vis the parent Li5V(PO4)2F2. We ascribe this to the creation of lithium vacancies within the structure that open up pathways for ion transport.

Critical Slowing Down of Triangular Lattice Spin-3/2 Heisenberg Antiferromagnet Li7RuO6 via 7Li NMR

We report on 7 Li NMR studies of single crystals of the triangular-lattice Heisenberg antiferromagnet Li 7 RuO 6 . A slow critical divergence with a wide critical region of | T / T N -1|≤7 was observed in 7 Li nuclear spin–lattice relaxation rate. The slowing down of staggered spin fluctuations was analyzed in a renormalized classical region of a two-dimensional triangular-lattice nonlinear sigma model. Spin stiffness constant was found to decrease to about 20% of its value in spin-wave approximation. The effect of spin frustration, e.g., Z 2 vortex excitations on critical phenomena, is suggested.

Emergence of Antiferromagnetic Correlation in LiTi2-xVxO4 via 7Li NMR

We report 7 Li NMR studies of V-substitution effects on the spinel oxide superconductor LiTi 2 O 4 ( T c =13.4 K). In LiTi 2- x V x O 4 ( x =0–0.4), the V substitution for the Ti site suppressed the relative volume fraction of superconductivity faster than T c . From the observation of a fairly homogeneous increase in 7 Li nuclear spin–lattice relaxation rate, we conclude that the V substitution changes electron correlation effects through electron carrier doping from quarter electron filling 3 d 0.5 to 3 d 1.5 and then the antiferromagnetic correlation emerges.

Effects of Salt and Nanoparticles on the Segmental Motion of Poly(ethylene oxide) in Its Crystalline and Amorphous Phases: 2H and 7Li NMR Studies

We use (2)H NMR to investigate the segmental motion of poly(ethylene oxide) (PEO) in neat and nanocomposite materials that do and do not contain salt. Specifically, in addition to a neat low-molecular-weight PEO, we study mixtures of this polymer with TiO 2 nanoparticles and LiClO 4. To characterize the polymer dynamics over a wide range of time scales, we combine (2)H NMR spin-lattice relaxation, line-shape, and stimulated-echo analyses. The results consistently show that the presence of nanoparticles hardly affects the behavior of the polymer, while addition of salt leads to substantial changes; e.g., it reduces the crystallinity. For neat PEO and a PEO-TiO 2 mixture, stimulated-echo spectroscopy enables measurement of rotational correlation functions for the crystalline phase. Analysis of the decays allows us to determine correlation times, to demonstrate the existence of a nonexponential relaxation, which implies a high complexity of the polymer dynamics in the crystal, and to show that the reorientation can be described as a large-angle jump. For a PEO-TiO 2-LiClO 4 mixture, we use (2)H and (7)Li NMR to study the polymer and the lithium dynamics, respectively. Analysis of the (7)Li spin-lattice relaxation reveals a high lithium ionic mobility in this nanocomposite polymer electrolyte. The (7)Li stimulated-echo decay is well described by a stretched exponential extending over about 6 orders of magnitude, indicating that a broad and continuous distribution of correlation times characterizes the fluctuations of the local lithium ionic environments.

Mimicking Biological Cation‐Transport Based on Sphere‐Surface Supramolecular Chemistry: Simultaneous Interaction of Porous Capsules with Molecular Plugs and Passing Cations

Spherical capsules of the type [{(Mo)Mo(5)}(12){Mo(2)(ligand)}(30)](n-) exhibiting 20 {Mo(9)O(9)} pores with crown ether functions allowed us to perform a sophisticated study of the title phenomenon based on synthetic work as well as NMR spectroscopy. The pores of the host system interact in solution specifically with guests that can be noncovalently bonded, such as formamidinium and acetamidinium cations, while having different affinities to the pores. The exchange between the guest species present in solution and in the pores was investigated, including, besides the extreme scenarios of complete pore closing and complete opening, that of stepwise pore plugging. Because of this option it was possible to model for the first time passive transmembrane cation transport based on gated pores/channels. These have the appropriate dimensions and can even adopt different structure flexibilities in response to different cations. The present investigation is based on related syntheses as well as on numerous detailed (7)Li NMR studies of Li(+) transport/exchange equilibria in dependence of the pore environment/guest situations. One compound containing capsules with sulfate ligands (2) could be obtained in which all the pores are plugged with formamidinium cations and another corresponding one was obtained with additionally encapsulated Ca(2+) ions (3); these were taken up after temporary release of some of the formamidinium plugs/guests upon short heating of the related solution.

6,7Li NMR study of ion mobility on the molecular scale in lithated imidazole complexes

Two model compounds, lithium imidazolium (LiIm) and lithium 2-undecylimidazolium (und-LiIm), were synthesized. These materials are chosen as models of potential lithium ion conductors for use as electrolytes in lithium batteries. Solid-state NMR was used to provide information on the microscopic interactions including ionic mobility and ring reorientations which govern the efficiency of conductivity. Lithium imidazolium was mixed with lithium methylsulfonate, generating a doped complex in which a doubly lithiated imidazole ring was inferred based on the 7Li NMR chemical shifts. Our research includes 6,7Li variable temperature MAS NMR experiments at intermediate spinning speeds, relaxation studies to determine spin-lattice relaxation times ( T 1) of lithium ion hopping, and 2D exchange spectroscopy to determine possible chemical exchange processes. The possibility of 2-site ring reorientation for the doubly lithiated imidazole ring was supported by exchange spectroscopy. Comparisons of spin-lattice relaxation times and corresponding activation energies of the lithium imidazolium and the doped complex point to a higher degree of mobility in the latter. Lithium 2-undecylimidazolium was prepared and exhibited a lower melting point than the parent lithium imidazolium, as expected. This small molecule was chosen as representative of a side-chain functionalized polyethylene-based material. 7Li MAS spectra show mainly the presence of the doubly lithiated imidazole ring in pure und-LiIm, and in the LiCH 3SO 3–und-LiIm mixture. The data clearly indicate local mobility of the lithium ions in the materials.

Lithiation of ramsdellite–pyrolusite MnO 2; NMR, XRD, TEM and electrochemical investigation of the discharge mechanism

Electrolytic manganese dioxide (EMD) is made in aqueous sulfuric acid and neutralized or ion exchanged with aqueous lithium hydroxide before use in Li batteries. Solid state Li NMR studies show that Li is present on surface and vacancy sites and migrates into Mn (III) related sites after heat treatment to remove water. During heat treatment the MnO 2 rearranges from ramsdellite/pyrolusite intergrowth EMD to a defect pyrolusite heat-treated manganese dioxide (HEMD). EMD exhaustively treated with lithium hydroxide solution has 40–50% of the protons in EMD exchanged for Li ions to produce a structurally unchanged γ-MnO 2. Li magic angle spinning (MAS) NMR reveals that this lithiated material contains lithium in cation vacancy and Mn (III) related sites in the MnO 2 lattice in addition to ionic Li on the surface. During heat treatment, the vacancy lithium content prevents the ramsdellite to pyrolusite rearrangement in HEMD formation. Instead, an ordered ramsdellite/pyrolusite intergrowth of lithiated manganese dioxide (LiMD) is formed with an approximate composition of 50% ramsdellite and 50% pyrolusite. Li MAS NMR of LiMD shows Li resonances near 280 and 560 ppm, consistent with Li transition from surface and cation vacancy sites into the ramsdellite lattice. LiMD discharged against lithium shows two processes, one near 3.1 V, the other about 2.8 V. Li MAS NMR studies show the initial reduction results a lithium resonance near 560 ppm associated with Li near a mixed valence Mn (III/IV) environment followed by appearance of a resonance near 100 ppm consistent with a Li environment near Mn (III). TEM studies of the reduced material show initial expansion of the ramsdellite lattice accompanied by a loss in crystallinity in the 3.1 V discharge process followed by disappearance of the pyrolusite content via conversion to ramsdellite in the second discharge process.

Synthesis, Structure, and Photocatalysis in a New Structural Variant of the Aurivillius Phase: LiBi4M3O14 (M = Nb, Ta)

Two new compounds, LiBi4Nb3O14 and LiBi4Ta3O14, have been synthesized by the solid-state method, using Li2CO3, Bi2O3, and M2O5 (M = Nb, Ta) in stoichiometric quantities. These compounds crystallize in the monoclinic C2/c space group with a = 13.035(3) A, b = 7.647(2) A, c = 12.217(3) A, beta = 101.512(4) degrees , V = 1193.4(5) A3 , and Z = 4 and a = 13.016(2) A, b = 7.583(1) A, c = 12.226(2) A, beta = 101.477(3) degrees , V = 1182.6(5) A3, and Z = 4, respectively. These are isostructural and the structure along the b axis consists of layers of [Bi2O2]2+ units separated by layers of LiO4 tetrahedra and NbO6 octahedra hence depicting an unusual variation in the Aurivillius phase isolated for the first time. The presence of lithium has been confirmed by 7Li NMR studies. ac impedance measurements and variable temperature (7)Li NMR studies indicate oxygen ion conductivity in these materials. The UV-visible spectra suggest a band gap of 3.0 eV for LiBi4Nb3O14 and 3.5 eV for LiBi4Ta3O14, respectively, and the associated studies on degradation of dyes and phenols render these materials suitable for photocatalysis.

7Li NMR study of ionically conducting glasses

ABSTRACTTemperature dependence of 7Li NMR was measured in 50Li20-50B203 glasses. A new method for the analysis of motional narrowing of the line width (MNLW) incorporating Kohlrasuch-Williams-Watt (KWW) function, exp(-(t/τ)β) is presented. The obtained activation parameters are compared with that from conductivity. It was shown that MNLW can be explained by the same activation energy from conductivity. It was found that electrical relaxation time was an order of magnitude smaller than that from those from NMR line width. At high temperature region, where the line is well narrowed, a residual line width was observed. It is as large as 1 kHz, and gradually decreases with the increase in temperature. It was explained that there is a mobility difference in lithium ions in this glass. These results suggest that some fraction of ions are highly mobilized in the glass.

Electrical conductivity and 6,7Li NMR studies of Li 1 + yCoO 2

The battery cathode material LiCoO 2 was synthesized with a deliberate excess of Li, according to Li 1 + y CoO 2, where y = 0.08 and 0.35 (nominally). The effect of divalent doping with Mg 2+ was also explored for some samples, with y values of 0.0 (stoichiometric) and 0.08. Electrical conductivity measurements of the stoichiometric material, without Mg, as functions of oxygen partial pressure and temperature exhibit p-type semiconducting behaviour and suggest that the defects primarily responsible for the generation of holes are cobalt ion vacancies. Excess Li increases the electrical conductivity, while the incorporation of Mg leads to a more dramatic enhancement in conductivity, the latter interpreted as a transition to metallic behaviour. NMR spectroscopic measurements of both 6,7Li isotopes suggest that only a small fraction (< 20%) of the excess Li in the y = 0.35 material enters the structure ionically while reducing the formal Co valence. Most of the excess consists of Li 2CO 3 and possibly other impurity phases, the former also having been identified by X-ray diffraction. Another small portion of the excess Li (about 10%) appears to enter interstitial sites in close proximity to paramagnetic Co 2+ ions.

Lithium Insertion Study in Vanadium Oxide Bronze by NMR and X Ray Diffraction

The insertion of lithium in vanadium pentoxide at high temperature is followed both by Xray diffraction and 7 Li NMR studies. A correlation between the lithium sites found by structure determination and the isotropic chemical shifts is established and a mechanism of the lithium insertion proposed. Calculations of the valence of the vanadium atoms and the simulation of NMR spectra allows to localise the V4 + in the highest lithium rate phases