Li Exchange Research Articles

Ultraslow Li Exchange Processes in Diamagnetic Li2ZrO3 As Monitored by EXSY NMR

Two-dimensional (2D) 6Li exchange magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy was used to probe extremely slow lithium hopping processes in a polycrystalline powder sample of lithium zirconate, Li2ZrO3. In agreement with the crystal structure of Li2ZrO3, the 6Li MAS NMR spectra recorded are composed of two signals (− 0.10 and 0.26 ppm) with equal intensity. They reflect the two magnetically (and electrically) inequivalent Li sites in Li2ZrO3. The mixing-time dependent 2D MAS NMR spectra, which were acquired at a bearing gas temperature of ca. 310 K, clearly reveal off-diagonal intensities indicating Li exchange processes with exchange rates as low as 60 jumps/hour. To our knowledge, this is by far one of the slowest Li solid-state diffusion processes ever probed by 6Li 2D exchange MAS NMR spectroscopy (submitted to J. Phys. Chem. C, 2013).

The Influence of Boronate Groups on the Selectivity of the Br–Li Exchange in Model Dibromoaryl Boronates

AbstractThe selectivity of the Br/Li exchange reaction of 6‐butyl‐2‐(2,5‐dibromophenyl)‐1,3,6,2‐dioxazaborocane (2,5‐Br2C6H3B(OCH2CH2)2NBu) and the analogous anionic derivatives, 2,5‐Br2C6H3B(OiPr)3Li and 2,5‐Br2C6H3BF3K, was investigated using nBuLi as the lithiating reagent. In the case of the former compound there was a slight preference for lithiation at the 5‐position. For 2,5‐Br2C6H3B(OiPr)3Li, the lithiation occured exclusively at C5, but for 2,5‐Br2C6H3BF3K, 2‐lithiation was preferred. Calculations performed for the lithiation of ortho‐ and meta‐brominated phenyl boronates revealed that ortho‐lithiated aryl boronates are thermodynamically more stable, but that the Br/Li exchange is generally dictated by kinetics, which accounts for the variation of selectivity depending on the type of boronate group. In addition, the successful generation of the 2,5‐dilithiophenyl boronate species 2,5‐Li2C6H3B(OCH2CH2)2NBu by a double Br/Li interconversion is reported. The Br/Li exchange in the related 6‐butyl‐2‐[3‐(2,5‐dibromothienyl)]‐1,3,6,2‐dioxazaborocane, 2,5‐Br2‐3‐ThB(OCH2CH2)2NBu, occured preferentially at the 5‐position, but the product was readily transformed into the more stable 2‐lithiated isomer. The use of 2 equiv. of nBuLi resulted in the efficient formation of the dilithiated species, 2,5‐Li2‐3‐ThB(OCH2CH2)2NBu. The obtained lithiated aryl boronates were converted into functionalized arylboronic acids by treatment with selected electrophiles.

Fabrication and electrochemical performance of lithium polymer battery using mesoporous silica/polymer hybrid electrolyte

Development of all solid-state Li secondary based on the use of dry polymer or inorganic electrolytes is vital as they will be free of solvent leakages and improve inflammability. However, both are still under development for many years due to low ionic conductivity, poor mechanical property and/or large internal impedance associated to poorly defined interfaces. In this paper, we report on a preparation and physicochemical property of mesoporous silica (MPS)/Li conductive polyethylene oxide (Li-PEO)-based polymer hybrid electrolytes (MPS+Li-PEO), and electrochemical performance of the Li/MPS+Li-PEO/LiFePO4 cell. The hybrid electrolytes showed an improvement of Li+ transportation number and a decrease of melting point and glass transition temperature, indicating a positive hybrid effect, or deviation from rule-of-mixtures behavior. The Li/MPS+Li-PEO/LiFePO4 cell showed a stable charge–discharge capacity of >70 mA h g−1 for 100 cycles at moderate temperature of 60°C and rate of 0.2 C, whereas severe capacity fade began after several of cycles for the cell using conventional Li-PEO electrolyte. AC impedance measurements revealed that the interface Li exchange between electrode and electrolytes related to the stable cyclic performance for the cell using hybrid electrolytes.

Matrix-dependent modulation of anisotropic effects on NMR spectra from 7Li+ and 23Na+ encapsulated in cryptands

(7)Li and (23)Na NMR spectra of the respective cations in gelatin and ι-carrageenan gels containing cryptand-[2.1.1] (for Li(+)) or cryptand-[2.2.2] (for Na(+)) displayed two transitions: the one at higher frequency corresponded to the cation surrounded by gel, the other to cation inside its appropriately sized cryptand. While binding to cryptands yielded much broader lines and shorter T (1) relaxation times, anisotropic splitting in first order (7)Li or (23)Na NMR spectra was not detected. Stretching the gels resulted in increasing the anisotropic electric field gradient tensor; thus, the NMR transitions of the cation in the gel were split (removal of degeneracy) to display its characteristic 3:4:3 triplet for spin=3/2 nuclei. The transitions of the cryptand-bound cations (Li(+)-cryptand-[2.1.1] and Na(+)-cryptand-[2.2.2]) showed different extents of interaction with the electric field gradient tensor depending on the composition of the gel matrix. The NMR signal for (7)Li(+)-cryptand-[2.1.1] in stretched gelatin gel showed a five-fold increased splitting as compared to the (7)Li(+) signal in the reference gel. In stretched ι-carrageenan gels, no anisotropic splitting from the cryptand-bound Li(+) was recorded. Steady-state irradiation envelopes or z-spectra showed evidence of Li(+) exchange between isotropic (cryptand) and anisotropic (gel) sites only at higher temperatures (55°C). For Na(+) bound to the cryptand-[2.2.2], anisotropic splitting (three-fold smaller compared with the (23)Na signal in the reference gel) was only recorded in stretched ι-carrageenan gels, whereas gelatin gels showed only anisotropic splitting for the (23)Na signal in the reference gel.

Insights into Li+ Migration Pathways in α-Li3VF6: A First-Principles Investigation

Magnetic, structural, and defect properties of lithium vanadium hexafluoride (α-Li3VF6) are investigated theoretically with periodic quantum chemical methods. It is found that the ferromagnetic phase is more stable than the antiferromagnetic phase. The crystal structure contains three inequivalent Li sites (Li(1), Li(2), and Li(3)), where Li(1) occupies the middle position of the triplet Li(2)-Li(1)-Li(3). The calculated Li vacancy formation energies show that vacancy formation is preferred for the Li(1) and Li(3) sites compared to the Li(2) position. The Li exchange processes between Li(1) ↔ Li(3), Li(1) ↔ Li(2), and Li(2) ↔ Li(3) are studied by calculating the Li(+) migration between these sites using the climbing-image nudged elastic band approach. It is observed that Li exchange in α-Li3VF6 may take place in the following order: Li(1) ↔ Li(3) > (Li(1) ↔ Li(2) > Li(2) ↔ Li(3). This is in agreement with recently published results obtained from 1D and 2D (6)Li exchange nuclear magnetic resonance spectroscopy.

Lithium defects and diffusivity in forsterite

Lithium is an important geochemical tracer used to infer the thermal and chemical evolution of minerals in the Earth’s upper mantle. Knowledge of point defect chemistry and diffusion is critical for the interpretation of Li distribution in minerals. Using quantum mechanical methods we show that in forsterite Li will be incorporated as bound interstitial–substitutional pairs. Furthermore, there will be temperature dependent fractionation of its two isotopes between the different sites. The fractionation decreases dramatically from 87.1‰ at 300K to 1.0‰ at 3000K. Diffusion is predicted to occur via two inter-related mechanisms: Mg–Li exchange, and a second, vacancy assisted interstitial mechanism. This behaviour is complex, facilitates migration of the heavier isotope and offers insights into observations of Li mobility and zoning in olivine, the most volumetrically important upper mantle mineral.

Near-Ambient Temperature Halogen-Lithium Exchange of p-Bromoanisole and Related Substrates: Flow/Batch Studies

With the advent of flow chemistry, the norm has been reactions executed on the laboratory scale with flow rates of only a few mL/min. We bring to the community’s attention our investigation of the halogen–lithium (X–Li) exchange in a continuous flow reactor, the Synthetron™. This novel reactor is capable of orders of magnitude greater rates of flow than current microreactors. This paper details a problematic X–Li exchange using our promoted hydrocarbon media formulated batch studies as well as the comparative derived flow studies. All of these studies have the additional feature of being performed at ambient or near-ambient temperatures. From the initial discoveries of Wittig and Gilman in the late 1930s, it has been known that X–Li exchange of p-bromoanisole (p-BrA) is plagued by a secondary ortho-lithiation. Fine-tuning of promoted hydrocarbon media batch studies can increase the ratio of p-LiA/o-Li-p-BrA; results from the Synthetron™ studies afford a much superior ratio of >100:1. Gram quantities of derivatives from this exchange (employing two reactors) can be prepared in a few seconds. Rationales for these observations will be presented as well as initial studies and discussion for bromobenzene (PhBr), m-bromoanisole (m-BrA), and p-iodoanisole (p-IA).

Effect of Ga incorporation on the structure and Li ion conductivity of La3Zr2Li7O12

In this paper we examine the effect of Ga doping on the structure and conductivity of the high Li ion content garnet-related system, La(3)Zr(2)Li(7)O(12). Without Ga doping, La(3)Zr(2)Li(7)O(12) is tetragonal and has low Li ion conductivity. The introduction of Ga leads to a change to a cubic unit cell, and a large enhancement in the conductivity. Prior structural studies of La(3)Zr(2)Li(7)O(12) have shown the presence of both tetrahedral and distorted octahedral sites for Li, and the low conductivity can be explained by the ordered nature of the Li distribution. The present structural study of La(3)Zr(2)Ga(0.5)Li(5.5)O(12) shows that Ga substitutes onto the tetrahedral site. Despite the presence of non-mobile Ga(3+) on the Li sites, the conductivity is enhanced as a result of the introduction of vacancies in the Li sites, and consequent disorder on the Li sublattice. Further work has suggested that over time in air, there is some H(+)/Li(+) exchange, and consequently some variation in the conductivity.

Thermally-induced cation disorder in LiFePO 4

LiFePO 4 has a fully ordered olivine structure in samples prepared by solid state reaction below ~ 800 °C but, with increasing temperature, a small amount of Li and Fe site exchange occurs reaching a value of about 4% just below melting at 975 °C. The disorder is reversible on annealing at lower temperatures and is detected by changes in lattice parameters and in cation site occupancies obtained by Rietveld refinement of X-ray powder diffraction data.

Straightforward Preparation of Functionalized α‐CF2‐Galactosides through an Oxygen to Carbon Acyl Migration

A privileged Glycon! A radical-addition Meerwein–Ponndorf–Verley (MPV) reduction sequence provides access to functionalized α-CF2-galactosides (see scheme). Introduction of a CF2Br group in the pseudo-anomeric position aided the transfer of an aglycon chain from O-2 to C-1′ through an intramolecular addition–reduction sequence, which involved a Br–Li exchange. This methodology gives access to a wide range of fluorinated C-glycosidic analogues of glycoconjugates.

Thermodynamic study of LiNaKLSX zeolites with different Li exchange rate for N 2/O 2 separation process

The process design for air separation based on adsorption requires knowledge of the following data: pure adsorption isotherms at different temperatures, multicomponent adsorption equilibrium data and kinetic data. In this paper, we present a complete study of oxygen and nitrogen adsorption at three temperatures on a set of Li exchanged NaKLSX zeolites. Pure gas isotherms were obtained for five different zeolites up to 2500 kPa at 303 K and for three of the five also at 288 and 318 K. Co-adsorption equilibria were analyzed for different compositions at 400 kPa and 303 K on the two zeolites which present the best adsorption capacities. Data were obtained with two volumetric apparatus constructed in lab. Furthermore, predictive binary equilibria obtained by Ideal Adsorbed Solution Theory (IAST) from pure component isotherms were compared with experimental mixture data. Finally, the zeolite which has the best adsorption capacities was formed with two different binders and their thermodynamic adsorption properties were compared to the original zeolite.

Antisite defects and Mg doping in LiFePO4: a first-principles investigation

Atomic and electronic structures of LiFePO4 with the antisite defect and Mg doping at Li and Fe sites have been investigated using first-principles density-functional theory with the on-site Coulomb interaction taken into account. It is demonstrated that the most favorable antisite defect type is the exchange defect, in which Li and Fe ions exchange positions. The resultant longer Fe–O bond and narrower band gap drop a hint that the electronic and ionic transport properties may be improved. For the case of Mg doping, Mg is preferentially doped at the Fe site instead of the Li site to form a new LiFe1−yMgyPO4 solid solution, leading to a higher ionic conductivity. Moreover, the dependence of the electrochemical properties on the concentration of Mg dopant has also been discussed.

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.

Ionic mobility in Nasicon-type LiMIV2(PO4)3 materials followed by 7Li NMR spectroscopy.

AbstractLithium mobility in LiM2(PO4)3 compounds, with M= Ge, Ti, Sn, Zr and Hf, has been investigated by 7Li Nuclear Magnetic Resonance (NMR) spectroscopy in the temperature range 100-500 K. From the analysis of 7Li NMR quadrupole interactions (CQ and η parameters), Li sites occupancy and exchange processes between structural sites have been studied. Below 250K, Li ions are preferentially located at M1 sites in rhombohedral phases, but occupy M12 sites in triclinic ones. At increasing temperatures, Li mobility has been deduced from spin-spin () and spin-lattice relaxation () rates. In this analysis, the presence of two relaxation mechanisms in plots has been associated with departures of conductivity from the Arrhenius behavior. At high temperatures, residence times at M12−T11−T11−T1 and M12 sites become similar and conductivity significantly increase. This superionic state can be achieved by enlarged order-disorder transformations in rhombohedral phases, or by sharp first order transitions in triclinic ones. Results described in the LiTi2(PO4)3 sample have been compared with those obtained in rhombohedral Li1+xTi2-xAlx(PO4)3 and LiTi2-xZrx(PO4)3 series showing respectively higher and lower conductivities. In the case of Li1.2Ti1.8Al0.2(PO4)3, displaying the highest reported conductivity, NMR results are discussed in relation with those obtained by Neutron Diffraction (ND) and Impedance Spectroscopy (IS). Diffusion coefficients determined by NMR Pulse Field Gradient (PFG) technique are similar to those deduced from Impedance Spectroscopy and NMR relaxation data.

On the mechanisms of ionic conductivity in BaLiF3: a molecular dynamics study

The mechanisms of ionic conductivity in BaLiF(3) are investigated using molecular simulations. Direct molecular dynamics simulations of (quasi) single crystalline super cell models hint at the preferred mobility mechanism which is based on fluoride interstitial (and to a smaller extent F(-) vacancy) migration. Analogous to previous modeling studies, the energy related to Frenkel defect formation in the ideal BaLiF(3) crystal was found as 4-5 eV which is in serious controversy to the experimentally observed activation barrier to ionic conductivity of only 1 eV. However, this controversy could be resolved by incorporating Ba(2+)↔ Li(+) exchange defects into the elsewise single crystalline model systems. Indeed, in the neighborhood of such cation exchange defects the F(-) Frenkel defect formation energy was identified to reduce to 1.3 eV whilst the cation exchange defect itself is related to a formation energy of 1.0 eV. Thus, our simulations hint at the importance of multiple defect scenarios for the ionic conductivity in BaLiF(3).

The general approach for the synthesis of substituted cyclobutenyl- and norbornadienyllithiums containing masked trifluoromethyl group

α,β-Unsaturated trifluoromethylketones of cyclobutene number containing trimethylstannyl substituent in β-position were firstly prepared by the addition of trimethylstannyllithium to the corresponding trifluoromethylenaminoketones. The protection of carbonyl function under basic conditions conserving the organometallic substituent was elaborated. The generation of corresponding organolithiums by Sn–Li exchange and their reactivity was studied.

Time-Resolved and Site-Specific Insights into Migration Pathways of Li+ in α-Li3VF6 by 6Li 2D Exchange MAS NMR

Two-dimensional (2D) exchange nuclear magnetic resonance (NMR) spectroscopy carried out under magic angle spinning (MAS) conditions is ideally suited to study site-specific Li diffusion parameters of cathode materials required for the target-oriented development of so-called high-energy density 4 V-lithium-ion batteries. In the present study, we took advantage of Li NMR hyperfine shifts to record temperature-variable 1D and mixing-time dependent 2D exchange MAS 6Li NMR spectra on α-Li3VF6 serving as both a potential cathode material as well as an application-oriented model substance with three magnetically inequivalent Li sites. By comparing the NMR results with structural details of the material we were able to obtain detailed insights into the migration pathways and Li exchange rates which are of the order of some hundreds of Li jumps per second at approximately 340 K. Site-specific Li jump rates τ−1 reveal the electrochemically active sites and provide information how to modify the material in order to increase its relatively low Li diffusivity found at room temperature.

ChemInform Abstract: Azoles. Part 9. Synthesis of Derivatives of Thieno(2,3-d)thiazole, 4H-Pyrrolo(2,3-d)thiazole, 2H-Pyrazolo(3,4-d)thiazole and Isoxazolo(3,4-d)thiazole from Thiazolidine-2,4-dione.

The aldehyde group of 2,4-dichlorothiazole-5-carbaldehyde was protected and the chlorine atom at position 2 was replaced by hydrogen and a methylthio group, via Cl → Li exchange, to give 4-chloro-thiazole-5-carbaldehyde and its 2-methylthio derivative, respectively. Ethyl 2-mercaptoacetate reacted with 4-chlorothiazole-5-carbaldehydes to give thieno[2,3-d]thiazoles. Saponification of ethyl thieno[2,3-d]thiazole-5-carboxylate and attempted decarboxylation of the resulting acid failed to yield enough of the parent thieno[2,3-d]thiazole to allow full characterisation owing to its high volatility.4-Azidothiazole-5-carbaldehydes were prepared by nucleophilic displacement of the chlorine atom in the corresponding 4-chlorothiazole-5-carbaldehyde and converted into alkenes and Schiff's bases by standard procedures. On being heated in toluene these afforded the corresponding 4H-pyrrolo-[2,3-d]thiazole or 2H-pyrazolo[3,4-d]thiazole. lsoxazolo[3,4-d]thiazole and its 2-methylthio derivative, both unstable, were obtained by heating the corresponding 4-azidothiazole-5-carbaldehyde in bromobenzene.

Formation of Acylsilenolates from Bis(acyl)trisilanes as the Silicon Analogues of Acylenolates

Reactions of bis(acyl)trisilanes with tris(trimethylsilyl)silyllithium in THF, followed by treatment of the resulting dark red solutions with alkyl halides, gave the Si-alkylated products and tetrakis(trimethylsilyl)silane, indicating the formation of lithium acylsilenolates via Si−Li exchange. Exothermic formation of lithium acylsilenolate was demonstrated by DFT calculations on a model reaction.

ChemInform Abstract: FC(SiMe3)3 and FC(SiMe3)2SnBu3: A Novel C1 Building Block for Fluoro Olefins.

Abstract Reaction of fluorotris(trimethylsilyl)methane and aldehydes is catalyzed by KF/18-Cr-6 to give 1,3-disubstituted 2-fluoro-2-propen-1-ols in one pot. On the other hand, SnLi exchange of bis(trimethylsilyl)-fluoro(tributylstannyl)methane with BuLi and subsequent treatment with an aldehyde afforded 1-fluoroalkenyltrimethylsilanes in moderate to good yields.