7Li NMR Research Articles

Electrochemical Delithiation/Relithiation of LiCoPO4: A Two-Step Reaction Mechanism Investigated by in Situ X-ray Diffraction, in Situ X-ray Absorption Spectroscopy, and ex Situ 7Li/31P NMR Spectroscopy

LiCoPO4 was synthesized by a solid-state and a supercritical solvo-thermal method. In situ X-ray absorption near-edge structure (XANES) experiments were evaluated on the basis of full-cycle experiments confirming the predominantly reversible character of the redox reaction. In situ X-ray diffraction (XRD) measurements were performed to follow structural changes during cycling indicating the existence of an intermediate phase upon cycling. The local phosphorus and lithium environments were studied by ex situ 31P and 7Li NMR at different states of charge proving the existence of an intermediate phase of the composition Li2/3CoPO4. On the basis of these findings, a model of the (de)lithiation process of LiCoPO4 is developed and discussed.

Competitive 7Li NMR study of the stoichiometry, stability and thermodynamic data for the complexation of Li+, Mn2+, Zn2+ and Cd2+ ions with two asymmetrical branched pentadentate (N5) amines containing pyridine moiety in ionic liquid–acetonitrile mixtures

Lithium-7 NMR spectroscopy was used to investigate the stoichiometry, stability and thermodynamic data of a Li+ complex with two asymmetrical branched amines, 3,6-bis(2-pyridylmethyl)-5-methyl-3,6-diazahexane-1-amine (A1) and 4,7-bis(2-pyridylmethyl)-6-methyl-4,7-diazaheptane-1-amine (A2) in 50–50 and 75–25wt% acetonitrile (AN)- [BMIM][PF6] (ionic liquid) mixture solution at various temperatures. A competitive 7Li NMR method was also employed to probe the complexation of Mn2+, Zn2+ and Cd2+ ions with A1 and A2 in the same solvent systems. The formation constants of the resulting complexes were evaluated from computer fitting of the mole ratio data to an equation that relates the observed chemical shifts to the formation constant. There is an inverse relationship between the complex stability and the amount of ionic liquid in the solvent mixtures. The temperature dependence formation constant was used for the evaluation of the enthalpy and entropy values for the complexation reaction. It was concluded that in all complexes, except for lithium ion, the resulting complex enthalpy is stabilized and the ΔH compensates the TΔS contribution. In the all studied solvent mixtures, the stability of the resulting 1:1 complexes was found to vary in the order Cd2+>Mn2+>Zn2+>Li+.

Paramagnetic shimming for wide-range variable-field NMR

We propose a new passive shimming strategy for variable-field NMR experiments, in which the magnetic field produced by paramagnetic shim pieces placed inside the magnet bore compensates the inhomogeneity of a variable-field magnet for a wide range of magnet currents. Paramagnetic shimming is demonstrated in 7Li, 87Rb, and 45Sc NMR of a liquid solution sample in magnetic fields of 3.4, 4.0, and 5.4T at a fixed carrier frequency of 56.0MHz. Since both the main-field inhomogeneity and the paramagnetic magnetization are proportional to the main-magnet current, the resonance lines are equally narrowed by the improved field homogeneity with an identical configuration of the paramagnetic shim pieces. Paramagnetic shimming presented in this work opens the possibility of high-resolution variable-field NMR experiments.

A role of lithiated sarcosine TFSI on the formation of single crystalline SrTiO3 nanocubes via hydrothermal method

Effective capping activity of lithiated sarcosine TFSI on the formation of single crystalline SrTiO3 nanocubes via hydrothermal method has been investigated. Lithiated sarcosine TFSI formation by zwitterionic transformation was confirmed by NMR and FTIR studies. 13C and 7Li NMR studies showed the stabilization of metal hydroxide anions by the secondary ammonium cations (–NH2+–) of lithiated sarcosine. The FESEM results revealed the formation of SrTiO3 nanocubes. TEM images showed the spherical and square shaped defects within the round edged cubic particles with the average size of 90nm and SAED pattern indicates the single crystalinity. The crystalinity and nanocubic shape of SrTiO3 were strongly influenced by lithiated sarcosine TFSI. Hence, we propose lithiated sarcosine TFSI as an effective capping agent for the synthesis of single crystalline SrTiO3 nanocubes.

Competitive 7Li NMR Study on the Mn2+, Zn2+ and Cd2+ Complexes of Two New Branched Hexadentate (N6) Amines Containing the Pyridine Moiety in Nitromethane and Acetonitrile Solutions

Lithium-7 NMR spectroscopy was used to investigate the stoichiometry and stability of a Li+ complex with two new branched amines, 4,7-bis(2-pyridylmethyl)-4,7-diazadecane-1,10-diamine (L1) and 4,8-bis(2-pyridylmethyl)-4,8-diazaundecane-1,11-diamine (L2), in acetonitrile and nitromethane. A competitive 7Li NMR method was also employed to probe the complexation of Mn2+, Zn2+ and Cd2+ ions with L1 and L2 in the same solvent systems. The formation constants of the resulting complexes were evaluated from computer fitting of the mole ratio data with an equation that relates the observed chemical shifts to the formation constant. In both solvents, the stability of the resulting 1:1 complexes was found to vary in the order Cd2+ > Zn2+ > Mn2+ > Li+.

A Study of Relaxation Effects of the Negative Electrode Tisnsb Using 119sn Mössbauer and 7li MAS NMR Spectroscopies

Owing to their high energy density, lithium rechargeable batteries are now considered the technology of choice for electrical energy storage in isolated sites, portable electronic devices and zero emission vehicles. However, in such systems there are often limitations in the energy density of the electrode materials, most commonly caused by weak capacities and limited electrode cycling life. Hence, research is currently underway to find new electrode materials capable of higher performance. Conversion type materials have recently been considered as a plausible alternative to conventional electrode materials, owing to their large gravimetric and volumetric energy densities. The ternary alloy TiSnSb was recently proposed as being a suitable negative electrode material in Li-ion batteries owing to its high electrochemical performance.1-4 TiSnSb has been shown to reversibly take up more than five lithium per formula unit, leading to reversible capacities of 540 mA h/g or 4070 mA h/cm3at a rate of 2C. Using complementary in situ operando X-ray diffraction (XRD) and in situ operando 119Sn Mössbauer spectroscopy, it was determined that during the first discharge, TiSnSb undergoes a conversion process leading to the simultaneous formation of Li-Sb and Li-Sn intermetallic compounds and, as a result, the corresponding electrochemical equation was proposed for Li insertion:TiSnSb + 6.5Li à Ti + Li3Sb + 0.5Li7Sn2 Some ambiguities however remain: A shifted, group of resonances appears on 7Li NMR spectra at approx. 20 ppm in addition to the expected contribution of Li3Sb at 3.5 ppm and a resonance at 8.5 ppm, tentatively assigned to Li7Sn2. The alloy Li7Sn3 has previously been reported at 18 ppm5, hence its presence cannot be ruled out. However, this phase has not been detected via 119Sn Mössbauer spectroscopy in this or any previous studies.In addition, changes in the local environments of Sn and Li nuclei have been detected upon OCV relaxation after the lithiation process, using 119Sn Mössbauer and 7Li NMR spectroscopies, respectively (Fig. 1). These results suggest an intrinsic instability of the phases formed at the end of the lithiation process and/or the formation of non-stoichiometric phases. 119Sn Mössbauer spectroscopy and 7Li MAS NMR have been combined in order to better understand the phases formed upon discharge and subsequent relaxation of a TiSnSb electrode. Both "in situ" and "ex situ" type experiments have been completed using the two techniques in order to understand the evolution of lithiated alloys during this increase of potential on Mössbauer signal and 7Li NMR shifts. Clearly, an investigation of relaxation using both Mössbauer spectroscopy and NMR is crucial to understand its origin and particularly important if this material is to be used in a practical device.Figure 1 : Relaxation profile after a C/2 lithiation of TiSnSb. Corresponding evolution of the 7Li NMR resonances and Mössbauer spectroscopy..[1]: Sougrati, M. T.; Fullenwarth, J.; Debenedetti, A.;Fraisse, B.; Jumas, J. C.; Monconduit, L. J. Mater. Chem. 2011, 21, 10069.[2]: Marino, C.; Sougrati, M. T.; Gerke, B.; Pöttgen, R.; Huo, H.; Ménétrier, M.; Grey, C. P.; Monconduit, L. Chem. Mater. 2012, 24, 4735.[3]: Marino, C. ; Darwiche, A. ; Dupré, N. ; Wilhelm, H. A. ; Lestriez, B. ; Martinez, H. ; Dedryvère, R. ; Zhang, W. ; Ghamouss, F. ; Lemordant, D. ; Monconduit, L. J. Phys. Chem. C 2013, 117, 19302.[4] : Wilhelm, H. A. ; Marino, C. ; Darwiche, A. ; Monconduit, L. ; Lestriez, B. Electrochem. Commun. 2012, 24, 89.[5] : Bekaert, E.; Robert, F.; Lippens, P. E.; Ménétrier, M. J. Phys. Chem. C 2010, 114, 6749

Ultrafast 1h and 7li Solid-State MAS NMR Studies of Materials for Next-Generation Li-Based Batteries

Li-based batteries are considered as one of the most promising advanced energy storage systems for electrical vehicles (EV) and stationary energy storage. However, their successful implementation in these emerging technologies is a significant challenge because energy requirements, system safety, and manufacturing costs are subject to more stringent demands than in current commercial batteries. Therefore, optimization of battery components such as electrode materials and electrolytes is a key step for the rational development of advanced battery systems. Solid-state magic-angle-spinning (MAS) NMR has emerged in the last decades as a unique technique for obtaining very accurate information on the atomic-level structure and dynamics of complex materials (1). This technique is sensitive to short-range order and therefore is not limited to crystalline materials. In particular, ultrafast MAS NMR (>60 kHz) generates spectral resolution enhancements that facilitate the identification of different species in complex systems (2).In this work, we present solid state NMR structural and dynamic characterizations of two highly Li-ion-conductive ceramic materials and a novel hybrid organic-inorganic composite. The results obtained by NMR were successfully applied to improve the performance of such materials.In the first part of this work, 7Li and 13C ultrafast MAS NMR were used to characterize a hybrid anode material composed of inorganic SnLi particles coated with a polymer phase based on the polymerization of vinyl-ethylene carbonate (VEC). The presence of 6 different SnLi alloy phases in the material was clearly differentiated together with some residual metallic lithium due to the different 7Li Knight shifts(3) of the individual compositions. 13C MAS NMR was used to characterize the organic phase in this compound. Results obtained provide a deeper understanding of the chemical composition and the possible synergistic interactions within this composite. In the second part of this work, ultrafast 1H and 7Li solid-state MAS NMR were applied in the study of two highly Li-ion-conductive ceramic materials. In particular, the effects of protonation by exposure to moisture on the conductivity of lithium in the perovskite Li3xLa2/3-x□1/3-2xTiO3 and the garnet Li7-3xGax□2xLa3Zr2O12were followed by NMR (where □=defect). The large grain boundary contributions to the overall Li-ion conductivity were monitored and the effects of moisture on the sintering of these electrolyte materials determined. Based on these results, an effective strategy to improve the total Li-ion conductivity of these materials was designed.(1) a) NMR of Quadrupolar Nuclei in Solid Materials, Roderick E. Wasylishen, Sharon E. Ashbrook, and Stephen Wimperis (Eds.) John Wiley & Sons Ltd, Chichester, UK (2012). b) Solid-State NMR in Materials Science: Principles and Applications, Vladimir I. Bakhmutov, CRC Press(2011). c) NMR Crystallography, Robin K. Harris, Roderick E. Wasylishen, and Melinda J. Duer (Eds.), Wiley, Chichester (2009).(2) I. Bertini, L. Emsley, M. Lelli, C. Luchinat, J. Mao, G. Pintacuda. J. Am. Chem. Soc. 2010, 132, 5558-9.(3) E. Bekaert, F. Robert, P. E. Lippens, and M. Menetrier. J. Phys Chem. C 2010, 114, 6749-6754.

Microsolvation, aggregation, and pseudomonomolecular, ionic sp2-stereoinversion mechanism of two exocyclic β,β-di-tert-alkyl-α-arylvinyllithiums

A THF-solvated, crystalline, exocyclic alkenyllithium, (tert-alkyl)2CC(Li)–Ph, was synthesized and shown to be a disolvated dimer in the solid state and in toluene as the solvent; increasing amounts of the monomeric species emerged on cooling the toluene solution. In THF as the solvent, only the trisolvated monomer was present and identified as a contact ion pair (CIP) through its scalar 13C,6Li NMR coupling. This ground-state needs only one further THF ligand as a catalyst for breaking the C–Li bond with formation of a tetrasolvated, solvent-separated ion pair (SSIP) on the way to the transition state of cis/trans sp2-stereoinversion. The ensuing pseudomonomolecular, ionic mechanism is confirmed by low pseudoactivation parameters: enthalpy ΔHψ‡ = 6.9(3) kcal mol−1; entropy ΔSψ‡ = −23.3(9) cal mol−1 K−1. Similar parameters were found with 2,6-dimethylphenyl in place of Ph.

Transport and Electrochemical Properties of Three Quaternary Ammonium Ionic Liquids and Lithium Salts Doping Effects Studied by NMR Spectroscopy

Ionic liquids (IL) composed of a quaternary ammonium cation having an ether chain, N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium (DEME) are electrochemically stable and used in electric double layer capacitors and also one of important candidates to use lithium secondary batteries. In this study, three DEME-based ILs with anions BF4, CF3BF3, and N(SO2CF3)2 were studied by measuring temperature dependences of ionic conductivity σ, viscosity η and density ρ. Also ion diffusion coefficients Danion and Dcation were obtained by NMR spectroscopy in the wide temperature range. Using the classical Stokes–Einstein (SE) and Nernst–Einstein (NE) equations, the relationships between η and D, and σ and D were evaluated. The lithium salt doping effects were studied by 7Li NMR spectroscopy. The lithium ion diffusion was slower than other ion diffusion at every temperature. Arrhenius-type plots of 7Li T1 showed minima in the three doped samples. Then one-jump distance of lithium ion was estimated in the temperature range between 273 and 373 K.

Enhancement of Stannylene Character in Stannole Dianion Equivalents Evidenced by NMR and Mössbauer Spectroscopy and Theoretical Studies of Newly Synthesized Silyl-Substituted Dilithiostannoles

Dilithiostannoles, which are aromatic tin-containing ring compounds, were proposed to have stannylene character, as judged from their NMR analysis. We herein report on the synthesis of silyl-substituted dilithiostannoles, which were characterized by NMR spectroscopy and X-ray diffraction analysis. The silyl-substituted derivatives also exhibit features characteristic of aromatic dilithiostannoles such as 7Li NMR signals at high-field area and no C–C bond alternation in the stannole rings. Theoretical calculations and the 119Sn NMR chemical shifts revealed that the stannylene character in the silyl-substituted dilithiostannoles is enhanced due to greater interaction between 5p (Sn) and LUMO (butadiene) in comparison to those in alkyl and aryl derivatives. The 119Sn Mössbauer spectra of dilithiostannoles were measured for the first time, indicating that each of the tin atoms in dilithiostannoles can be characterized as having Sn(II) character.

Single Crystal Nuclear Magnetic Resonance Studies of LiMnxFe1-XPO4

LiMPO4 are orthorhombic crystals, belonging to the olivine family and exhibit exceptionally high applicability for electrochemical energy storage in lithium-ion secondary batteries due to their charge storage capacity, chemical and thermal stability, and cost. Furthermore, mixed transition metal ion compounds Li(M,M’)PO4 are particularly promising cathode materials because the redox voltage increases as from Fe to Mn, Ni, Co 1and the mixed compounds can be tailored for specific applications.The aim of these studies is to better understand the key role played by the transition metals such as Fe, Mn and particularly their mixtures in determining the properties of these materials. Single crystal 7Li and 31P NMR studies are used to obtain precise information on the magnetic environments of the lithium ions and phosphate groups which may ultimately be correlated with processes and structural features that determine the electrochemical behavior of these olivine phosphates.By measurements of 7Li and 31P NMR frequencies, i.e. ν = B0∙σ∙Ι, where B0 is the applied field and Ι is the nuclear spin, with crystal orientation, it is possible to determine interaction tensor components {σij } giving rise to the lithium and phosphorus shifts. The series of the single crystals of LiMPO4 were prepared by a reciprocal salt flux growth technique, which allows the facile preparation of single crystals up to 1 cm across with well-developed facets at relatively low temperatures. Crystals for the NMR measurements present their natural faceting2.X-ray diffraction measurements were performed in order to identify the principal crystallographic axes [100], [010] and [001] of the samples. Subsequently the crystals were fixed to a rigid insert in the NMR probe, which was mounted onto a goniometer and inserted between the gap of a permanent magnet (B0=2.1T). The use of a relatively low field strength allowed for acquisition of the entire rotation pattern within the spectrometer bandwidth. Rotations were made with the goniometer shaft perpendicular to applied magnetic field, in this way it was possible to generate 24 spectra, one every 15o, for each crystallographic axis [100],[010] and [001].Previous studies3 showed that in the case of 31P, crystals exhibit large (paramagnetic) shifts on the order of 3000ppm, primarily due to the hyperfine interactions between the unpaired electron spins of the paramagnetic ion and the phosphorus nuclei.The 7Li resonances are also strongly affected by the paramagnetic susceptibility though not to the same extent as 31P. However in addition, there is a nuclear quadrupole interaction which splits the resonance and provides information concerning the electric field gradientIn addition to the endpoints (Fe and Mn analogues), we present an NMR analysis of the mixed transition metal ion compounds LiFexMn1-xPO4 , where x = 0.25, 0.5, and 0.75 in order to shed some light on the degree of cation disorder between the lithium, phosphorus, and transition metal sites that can result in substantial degradation of cathode performance particularly with regard to reduced rate capability.This research was supported by the U.S. Department of Energy

Effect of TiO2 nanoparticle additions on the conductivity of network polymer electrolytes for lithium power sources

Network copolymer electrolytes were synthesized from polyether (polyester) diacrylates with different structures and chain lengths of polyester diacrylate and polyethylene glycol diacrylate. The optimum matrix for ion transport in the electrolyte was formed from only one type of oligomer. The influence of TiO2 nanopowder additions (∼60 nm) on the conductivity of the copolymer electrolyte was studied. The addition of 10 wt % TiO2 led to an increase in the conductivity by an order of magnitude at 30°C; the effective activation energy decreased by 20%. At elevated temperatures, the mobility of polymer chains increased and the contribution of TiO2 nanoparticles in ion transport was only half of the order of magnitude of the conductivity at 100°C. The increase in the conductivity of the polymer electrolyte after the addition of TiO2 was presumably caused by the formation of a more mobile state of the lithium ion near the nanoparticle surface, as shown by pulsed field gradient (PFG) 7Li NMR.

Enhanced Electric Double-Layer Capacitance by Desolvation of Lithium Ions in Confined Nanospaces of Microporous Carbon

Carbon electrodes with specific microporous structures are strongly desired to improve the performance of electric double-layer capacitors (EDLCs). We report solvated states of Li ions in confined carbon micropores affecting specific capacitance. The average Li(+) solvation number of 1 M LiClO4/propylene carbonate (PC) electrolyte introduced into porous carbon electrodes was determined using Raman spectroscopy and (7)Li NMR. Micropores with slightly larger pore size against the solvated molecules and the narrow two-dimensional spaces decreased the solvation number, enhancing specific capacitance. Hence, specific carbon morphology may be related to high EDL capacitance, and micropore structure is important in obtaining highly capacitive EDLC materials.

Solution structures of lithium amino alkoxides used in highly enantioselective 1,2-additions.

Lithium ephedrates and norcarane-derived lithium amino alkoxides used to effect highly enantioselective 1,2-additions on large scales have been characterized in toluene and tetrahydrofuran. The method of continuous variations in conjunction with 6Li NMR spectroscopy reveals that the lithium amino alkoxides are tetrameric. In each case, low-temperature 6Li NMR spectra show stereoisomerically pure homoaggregates displaying resonances consistent with an S4-symmetric cubic core rather than the alternative D2d core. These assignments are supported by density functional theory computations and conform to X-ray crystal structures. Slow aggregate exchanges are discussed in the context of amino alkoxides as chiral auxiliaries.

A rapid polyol combustion strategy towards scalable synthesis of nanostructured LiFePO4/C cathodes for Li-ion batteries

In the present study, carbon-coated lithium iron phosphate (LiFePO4/C) is prepared directly by a polyol-assisted pyro-synthesis performed under reaction times of a few seconds in open-air conditions. The polyol solvent, tetraethylene glycol (TTEG), acts as a low-cost fuel to facilitate combustion and the released exothermic energy promotes the nucleation and growth processes of the olivine nanoparticles. In addition, phosphoric acid (used as the phosphorous source) acts as a catalyst to accelerate polyol carbonization. The structure analysis of the as-prepared LiFePO4/C using X-ray, neutron diffraction and 7Li NMR studies suggested the efficacy of the rapid technique to produce highly crystalline phase-pure olivine nanocrystals. The electron microscopy and particle-size distribution studies revealed that the average particle diameters lie below 100 nm and confirmed the presence of a surface carbon layer of 2–3 nm thickness. The thermal and elemental studies indicated that the carbon content in the sample was approximately 5 %. The prepared LiFePO4/C cathode delivered capacities of 162 mA h g-1 at 0.1 °C rates with impressive capacity retention for extended cycling. The polyol-assisted pyro-synthesis, which evades the use of external energy sources, is not only a straightforward, simple and timely approach but also offers opportunities for large-scale LiFePO4/C production.

Charge transfer in Li/CFx–silver vanadium oxide hybrid cathode batteries revealed by solid state 7Li and 19F nuclear magnetic resonance spectroscopy

Solid state 7Li and 19F magic angle spinning nuclear magnetic resonance (MAS NMR) experiments are conducted on several cathodes containing CFx–Silver vanadium oxide (CFx–Ag2V4O11) hybrid cathodes discharged to 50% depth of discharge (DoD) and stored at their open-circuit voltage for a period of one and three months. Three carbonaceous sources for the CFx phase are investigated: petroleum coke-based, fibrous, and mixed fibrous. For each hybrid cathode, a measurable increase in the relative amount of lithium fluoride is observed after a three month resting period in both the 7Li and 19F NMR spectra. These changes are attributed to lithium ion migration from the silver vanadium oxide to the CFx phase during the resting period, and help clarify the mechanism behind high power handling capability of this cathode.

Characterization of Bulk and Surface Chemical States on Electrochemically Cycled LiFePO4: A Solid State NMR Study

Bulk and surface chemical states were both investigated for electrochemically delithiated LixFePO4 using 7Li and 31P MAS NMR spectroscopy. The quantitative lithium extraction/insertion from LiFePO4 and the reversible two-phase reaction behavior between LiFePO4 and FePO4 were confirmed on electrochemical operation. The 7Li and 31P NMR spectra of the fully charged LixFePO4 evidenced a single Li-poor phase Li0.05FePO4 instead of a biphasic mixture of 0.05LiFePO4 and 0.95FePO4. Simultaneous growth of LixPOyFz was also shown as a surface film component on the charged electrodes, which dynamically increased and decreased in intensity during charging and discharging reactions, respectively. The electrode surface was further characterized with XPS to discuss the surface film formation during electrochemical cycles. Combined chemical state analyzes by NMR and XPS spectroscopies suggested that the degradation of LiPF6 salt occurred from the initial redox cycles, but that of solvent occurred after multiple cycling. The deposition of carbonaceous species would be related to a small capacity fading observed after the multiple charge-discharge cycles.

Preparation, structure and electrochemistry of LiFeBO3: a cathode material for Li-ion batteries

The preparation of high-purity LiFeBO3 has been reported, which ensures an accurate crystal structure determination through synchrotron XRD, neutron powder diffraction, single crystal XRD combined with 6Li NMR and 57Fe Mössbauer spectroscopies.

Synthesis and Structural Characterization of a Series of Group 11 2,2-Dialkyl-1,3-dicyclohexylguanidinate Complexes

The addition of either lithium dimethylamide or lithium diethylamide to a tetrahydrofuran (THF) solution of 1,3-dicyclohexylcarbodiimide yielded THF adducts of lithium 2,2-dimethyl-1,3-dicyclohexylguandidinate (1) and lithium 2,2-diethyl-1,3-dicyclohexylguandidinate (2), respectively. One equivalent of either 1 or 2 was subsequently reacted with one equivalent of Group 11 halide (CuCl, AgBr, and AuCl) to generate oligonuclear complexes with the general formula {M[CyNC(NR2)NCy]}n where M, R, and n are respectively Cu, CH3, 2 (3); Cu, CH2CH3, 2 (4); Ag, CH3, 3 (5); Ag, CH2CH3, 3 (6); Au, CH3, 2 (7); and Au, CH2CH3, 2 (8). Compounds 1–8 were characterized by single-crystal X-ray diffraction. The bulk powders for all complexes were found to be in agreement with the crystal structures based on elemental analyses, Fourier transform infrared spectroscopy, and 1H, 13C, and 7Li NMR studies. The unique structural aspects of this family of Group 11 complexes are highlighted.

Correlations between lithium local structure and electrochemistry of layered LiCo1−2xNixMnxO2oxides:7Li MAS NMR and EPR studies

Advanced (7)Li MAS NMR technologies and high frequency EPR are combined to identify structural motifs and their relation to electrochemical properties of layered lithium-cobalt-nickel-manganese oxides LiCo1-2xNixMnxO2 (0 < x ≤ 0.5) used as cathode materials in lithium ion batteries. Structural-chemical shift regularities were established by systematic variation of the ratio of diamagnetic Co(3+) to paramagnetic Ni/Mn ions with variable valences. While EPR allows identifying the oxidation state of transition metal ions inside the layers, (7)Li NMR probes the local structure of Li with respect to transition metal ions located in two adjacent layers. For assignment of the lithium chemical shifts, we examine first magnetically diluted LiCo1-2xNixMnxO2 with x = 0.02, where paramagnetic ions are stabilized only in Mn(4+) and Ni(3+) form. Then the studies are extended towards the intermediate compositions with x = 0.10 and 0.33, containing simultaneously paramagnetic Mn(4+), Ni(3+) and Ni(2+) ions and diamagnetic Co(3+) ions. The benefit of using NMR with ultrafast spinning rates is demonstrated for the end composition LiNi0.5Mn0.5O2 having only paramagnetic Ni(2+) and Mn(2+) ions. The local structure of Li is quantified in respect of the number of Ni(2+) and Mn(4+) neighbors. It has been demonstrated that Ni(2+) and Mn(4+) are non-randomly distributed around Li and their distribution depends on the method of synthesis. The extent of local cationic order and its effect on the electrochemical properties of LiNi0.5Mn0.5O2 are discussed.