EELS spectroscopy of iron fluorides and FeFx/C nanocomposite electrodes used in Li-ion batteries.

A new type of positive electrode for Li-ion batteries has been developed recently based on FeF3/C and FeF2/C nanocomposites. The microstructural and redox evolution during discharge and recharge processes was followed by electron energy loss spectroscopy (EELS) to determine the valence state of Fe by measuring the Fe L3 line energy shift and from Fe L3/L2 line intensity ratios. In addition, transition metal fluorides were found to be electron beam sensitive, and the effect of beam exposure on EELS spectra was also investigated. The EELS results indicate that for both FeF3/C and FeF2/C nanocomposite systems, a complete reduction of iron to FeO is observed upon discharge to 1.5 V with the formation of a finer FeO/LiF subnanocomposite ( approximately 7 nm). Upon complete recharging to 4.5 V, EELS data reveal a reoxidation process to a Fe2+ state with the formation of a carbon metal fluoride nanocomposite related to the FeF2 structure.     

Atomistic insights into the conversion reaction in iron fluoride: a dynamically adaptive force field approach

Nanoscale metal fluorides are promising candidates for high capacity lithium ion batteries, in which a conversion reaction upon exposure to Li ions enables access to the multiple valence states of the metal cation. However, little is known about the molecular mechanisms and the reaction pathways in conversion that relate to the need for nanoscale starting materials. To address this reaction and the controversial role of intercalation in a promising conversion material, FeF(2), a dynamically adaptive force field that allows for a change in ion charge during reactions is applied in molecular dynamics simulations. Results provide the atomistic view of this conversion reaction that forms nanocrystals of LiF and Fe(0) and addresses the important controversy regarding intercalation. Simulations of Li(+) exposure on the low energy FeF(2) (001) and (110) surfaces show that the reaction initiates at the surface and iron clusters as well as crystalline LiF are formed, sometimes via an amorphous Li-F. Li intercalation is also observed as a function of surface orientation and rate of exposure to the Li, with different behavior on (001) and (110) surfaces. Intercalation along [001] rapid transport channels is accompanied by a slight reduction of charge density on multiple nearby Fe ions per Li ion until enough Li saturates a region and causes the nearby Fe to lose sufficient charge to become destabilized and form the nanocluster Fe(0). The resultant nanostructures are fully consistent with postconversion TEM observations, and the simulations provide the solution to the controversy regarding intercalation versus conversion and the atomistic rationale for the need for nanoscale metal fluoride starting particles in conversion cathodes.     

脉冲激光沉积CuF2薄膜的电化学性能

采用脉冲激光沉积法在不锈钢基片上制备了纳米结构的CuF2薄膜, 其充放电性能显示该薄膜具有540 mAh·g-1可逆容量, 对应于每个CuF2可与2.0个Li发生反应. 其循环伏安特性显示在2.2和2.8 V (vs Li/Li+)处出现了一对新的氧化还原峰. 充放电后薄膜的组成与结构通过非原位高分辨电子显微和选区电子衍射来表征. 结果揭示了纳米结构CuF2薄膜的电化学反应机理, LiF在过渡金属Cu的驱动下可以发生可逆的分解和形成.     

Metal atom oxidation lasers

Stimulated emission in the infrared was observed when fine wires, metallic films and graphite smears were exploded into oxidizing gases. Laser action was attributed to the following diatomic molecules: LiF, CF, CO, MgF, TiF, TiO, FeF, NiF, CuF, PtF, AuF, UF, and UO.     

Ab initio study of the diatomic fluorides FeF, CoF, NiF, and CuF

The late-3d transition-metal diatomic fluorides MF = FeF, CoF, NiF, and CuF have been studied using variational multireference (MRCI) and coupled-cluster [RCCSD(T)] methods, combined with large to very large basis sets. We examined a total of 35 (2S+1)|Lambda| states, constructing as well 29 full potential energy curves through the MRCI method. All examined states are ionic, diabatically correlating to M(+)+F(-)((1)S). Notwithstanding the "eccentric" character of the 3d transition metals and the difficulties to accurately be described with all-electron ab initio methods, our results are, in general, in very good agreement with available experimental numbers.     

Copper fluoride as a low-cost sodium-ion battery cathode with high capacity

Sodium-ion batteries（SIBs） are promising alternatives to lithium-ion batteries（LIBs） for large-scale energy storage considering the abundance and low cost of Na-containing resources. However, the energy density of SIBs has been limited by the typically low specific capacities of traditional intercalation-based cathodes. Metal fluorides, in contrast, can deliver much higher capacities based on multi-electron conversion reactions. Among metal fluorides, CuF₂ presents a theoretical speci...     

Phase equilibria in the cutting elements LiF–KCl–Li<Subscript>2</Subscript>WO<Subscript>4</Subscript> and LiF–KCl–LiKWO<Subscript>4</Subscript> of the quaternary reciprocal system Li,K‖F,Cl, WO<Subscript>4</Subscript>

The quaternary reciprocal system comprising fluorides, chlorides, and tungstates of lithium and potassium was partitioned into simplexes using graph theory, and a phase tree of the system was constructed. In the cutting triangles LiF–KCl–Li₂WO₄ and LiF–KCl–LiKWO₄ by differential thermal analysis, the melting points and compositions of ternary eutectics were determined, and the crystallization fields of phases are delineated. For each element of the state diagram, phase reactions were described. The compositions of crystallizing phases in the cutting triangles LiF–KCl–Li₂WO₄ and LiF–KCl–LiKWO₄ were confirmed by X-ray powder diffraction analysis.     

LiMSO(4)F (M = Fe, Co and Ni): promising new positive electrode materials through the DFT microscope

A theoretical study of the lithium intercalated LiMSO(4)F and deintercalated MSO(4)F systems, where M = Fe, Co and Ni has been performed within the framework of density functional theory. Beyond predictions of structural evolution and average voltages versus a lithium electrode, we have applied partial density of states and Bader's topological analysis of the electron density to the study of lithium deintercalation. Upon lithium extraction, charge rearrangement occurs for nickel between different d-orbitals, but with little net positive charge gain, while cobalt and iron atoms end up with a clear oxidized state. The participation of oxygen ions in accepting the electron of the lithium is thus enhanced for LiNiSO(4)F. However, this effect does not affect the long-range electrostatic interactions a lot in the lithiated phase, since the valence of all transition metals is very close due to initial lower oxidized state for the Ni atom in the host. It is found that this is not essentially a long-range electrostatic interaction within the lithiated phase but within the host which explains, at least partly, the increase in voltage by passing from Fe to Ni. Our results also shed light upon the possibility of getting an approximate evaluation of the local strain associated with delithiation from the atomic volume evolutions, which are also likely to affect the electrochemical potential.     

Reaktionen und Verknüpfungen von 1,2-Diaza-3-sila-5-cyclopentenen

Reactions and Bridging of 1,2-Diaza-3-sila-5-cyclopentenes 1,2-Diaza-3-sila-5-cyclopentenes react with butyllithium to give lithium salts. In reactions of the lithium salts with halosilanes ( 1–7 ), trimethyltinchloride (8) or methyliodide ( 9 ) substituted compounds are obtained by LiHal elimination. Bromosuccinimide brominates the methylene group of the ring system ( 10 ). Bridging of 1,2-diaza-3-sila-5-cyclopentenes by boryl and silyl groups are described ( 11–13 ). In the reaction of trifluorophenylsilane with lithiated 1 , 2-tert.-butyl-4-lithio-3,3,5-trimethyl-4-fluorodimethylsilyl-1,2-diaza-3-sila-5-cyclopentene, which is stable in solution, a second substitution takes place ( 14 ). The thermal elimination of LiF from lithiated 1 leads to the formation of the spirocyclic compound 15 . The n.m.r. and mass spectra of the compounds are reported.     

Phase equilibria in the ternary reciprocal system Li,Rb‖F,CrO4

The ternary reciprocal system of fluorides and chromates of lithium and rubidium was studied for the first time. The stable pair of salts LiF and Rb₂CrO₄ and also binary compounds on the bordering sides partition the system into five simplexes. Studying a number of polythermal sections allowed us to determine the melting points and compositions of two peritectics and three eutectics. The crystallization fields of phases in the system were demarcated, and phase equilibria were described.     

Mechanochemical reactions of fluorides with hemin

Hemin has two potential sites to react with fluorides, the peripheral acid groups and the central Fe^III cation. The mechanochemical reactions of hemin with fluorides (LiF, NaF, KF, CsF, NH₄F and AgF) were monitored using X-ray diffraction (XRD), and IR and Mössbauer spectroscopies. LiF and NaF were found inert when milled with hemin, however KF, CsF, NH₄F and AgF react at both hemin sites. At the iron site Cl⁻ is replaced by F⁻ with formation of KCl, CsCl, NH₄Cl, and AgCl, as detected by XRD, while with the peripheral acid groups, fluorides collect the acidic protons to form KHF₂, CsHF₂, NH₄HF and AgHF₂. The reactions of hemin with the reactive fluorides take place first at the iron site and then at the propionic acid groups.     

Copper Fluoride Luminescence during UV Photofragmentation of Bis(1,1,1,5,5,5-hexafluoro-2,4-pentanedionato)copper(II) in the Gas Phase

Gas phase 308 and 350-370 nm photolysis of bis(1,1,1,5,5,5-hexafluoro-2,4-pentanedionato)copper(II), Cu(hfac)(2), produces CuF as well as copper atoms and dimers. These metal-containing fragments, identified by luminescence spectroscopy, are studied under a variety of gas phase conditions ranging from 1 bar in a static chamber to 10(-4) mbar in a collision-free molecular beam. Copper atom and dimer luminescence is observed at the higher pressures, whereas at low pressures (total pressure no greater than the vapor pressure of the sample) exclusively CuF emission is observed. The a, A (omega = 0, 1, 2), B, and C excited states at 681.0, 567.6, and 505.1, and 491.7 nm are observed. The (3)Pi(0)(-) component of the A state is observed for the first time. The CuF luminescence obeys a quadratic power law with 308 nm excitation. The partitioning of excess energy into fragment degrees of freedom is determined from the intensities of the emission lines. The vibrational and rotational temperatures of the CuF fragment are in excess of 1700 K. Mechanisms of CuF formation, comparisons with the free ligand and with other volatile copper complexes, and the implications for laser-assisted chemical vapor deposition are discussed.     

Lithium insertion into YBa2Cu3O7

Atomistic computer simulation techniques are used to investigate the effects of lithium insertion into YBa₂Cu₃O₇. Attention is focused on various possible lattice sites occupied by the inserted lithium ions and pathways for their migration. The square-planar position in the Cu(2) layer is calculated to be the most energetically favorable. This is supported by the structural modeling of the ordered lithiated phase Li_0.33YBa₂Cu₃O₇. The calculated activation energies derived from migration profiles are in accord with experimental values and suggest fairly mobile lithium ions.     

Copper(ii) fluorophosphates

Eleven new copper fluorophosphate frameworks have been synthesised hydrothermally in a fluoride-rich medium, through the use of CuF(2) HPF(6) and monovalent metal fluorides as reactants. Products have been structurally characterised using single crystal X-ray diffraction. Reaction in fluoride-rich conditions produces chain, layer and three dimensional framework structures containing new and unusual structural features based on the linking of PO(3)F, PO(2)(OH,F)(2) and Cu(O,F)(n) polyhedra (n = 4-6). Analysis of these structures, in terms of the copper coordination environments and their linkage dimensionalities, shows that these features are dependent on fluoride-content of the reaction medium and, therefore, the level of fluoride ion incorporation into the product materials. Structures exhibiting inter-layer spaces and channels frequently have these lined by terminal fluoride anions of the PO(3)F, PO(2)(OH,F)(2) and Cu(O,F)(n) polyhedra.     

Poly- und spirocyclische Silylhydrazone – Synthese und Molekülstrukturen

Poly- and Spirocyclic Silylhydrazones — Synthesis and Molecular Structures Bulky aminotrifluorosilanes react with lithiated dimethylketone-hydrazone to give 1,2-diaza-3-sila-5-cyclopentenes — DSCP — ( 1, 2 ). The 4-silylated ( 3–5, 8–15 ) and siloxysilyl-substituted ( 17, 18 ) rings eliminate no halosilane or siloxane thermally. Lithiated 2 dimerises with LiF elimination to give the (2+2)cycloadduct of a 1,2-diaza-3-sila-3,5-cyclopentadiene ( 6 ). Lithiated DSCP reacts with MeSiF₂N(CMe₃)SiMe₂CMe₃ via a nucleophilic 1,3-methanide ion migration to form LiF and the spirocyclic compound 18 . A compound with spirocyclic silicon ( 21 ) is formed in the reaction of bis(1,2-diaza-3-sila-5-cyclopenten-4-yl)difluorosilane ( 19 ) and the lithium salt of dimethyl-ketone-tert-butylhydrazone. The crystal structures of 6 and 21 are reported.     

Matrix Infrared Spectroscopy and Quantum‐Chemical Calculations for the Coinage‐Metal Fluorides: Comparisons of Ar?AuF,Ne?AuF,and Molecules MF2 and MF3

The reactions of laser‐ablated Au, Ag, and Cu atoms with F₂ in excess argon and neon gave new absorptions in the M? F stretching region of their IR spectra, which were assigned to metal‐fluoride species. For gold, a Ng? AuF bond was identified in mixed neon/argon samples. However, this bonding was much weaker with AgF and CuF. Molecules MF₂ and MF₃ (M=Au, Ag, Cu) were identified from the isotopic distribution of the Cu and Ag atoms, comparison of the frequencies for three metal fluorides, and theoretical frequency calculations. The AuF₅ molecule was characterized by its strongest stretching mode and theoretical frequency calculations. Additional evidence was observed for the formation of the Au₂F₆ molecule.     

锂钛复合氧化物锂离子电池负极材料的研究

采用 3种化学方法合成锂钛复合氧化物 .应用X -射线衍射分析对其结构进行表征以及电化学性能测试 ,结果表明 :由Li2 CO3、TiO2 高温合成的锂钛复合氧化物为尖晶石结构的Li4Ti5 O12 .Li4Ti5 O12 电极在 1 .5V左右有一放电平台 ,充放电可逆性良好 ,即充电电压平台与此接近 ,且电极的比容量较大 ,循环性能良好 .以 0 .30mA·cm- 2 充放电时 ,首次放电容量可达 30 0mAh·g- 1,可逆比容量为 1 0 0mAh·g- 1,经多次充放电循环后 ,其结构仍保持稳定性 .试验电池测试表明 ,Li4Ti5 O12 可选作Li4Ti5 O12 /LiCoO2 锂离子电池的负极材料 .     

Synthesis,electrochemistry and thermal studies of fluoro and imidazole complexes of copper(II)

Complexes of the (H2Im)4[CuF6], (H2Im)2[CuF4(H2O)2] type (H2Im=imidazolium cation) and Cu(HIm)4X2 (X=Cl or Br; HIm=imidazole) have been prepared in aqueous solution by the interaction of CuO·nH2O with the respective halide in the presence of imidazole. Formation of a particular complex species has been shown to be dependent on the reaction solution pH and also on the nature of the halide. The complexes were characterised on the basis of FT-i.r., u.v.–vis. and e.s.r. spectroscopy and by measurement of magnetic susceptibilities and solution electrical conductivities. Cyclic voltammetry revealed a two-peak quasi-reversible response for [Cu(HIm)4Br2], while other complexes produced overall irreversible voltammographs. Thermal decomposition profiles are consistent with the proposed formulations.     

Effect of counterions on hypervalent interactions in prereaction complexes of S N 2 reactions of bisphenoid compounds of the second and third period elements

The electronic and molecular structures of the (LiF) _n XF _m complexes (X = C, N, O, F, Si, P, S, Cl; m = 1–4, n = 0, 1, 3) were studied by the ab initio (MP2(full)/6-311+G*) and density functional theory (B3LYP/6-311+G*) methods. All bisphenoid anionic structures XF _m ^? (X = C, N, O, F, Si, P, S, Cl; m = 2–5) of elements of the second and third periods, except carbon fluorides, are most stable in the hypervalent state of atoms with strongly elongated axial bonds. Carbon tetrafluoride forms a stable intermolecular F^?...CF₄ complex. In all cases of addition of the Li atom as a counterion, the most stable intermolecular complex of lithium fluoride with fluorides of elements is stabilized by the hypervalent interaction. In all cases when the counterion is complicated to lithium trifluoride, except for (LiF)₃CF₄ and (LiF)₃NF₃, the hypervalent structure with equal and elongated X-F axial bonds is stabilized. In the cases of the (LiF)₃CF₄ and (LiF)₃NF₃ complexes, the prereaction structures bound by the strong hypervalent interaction are stabilized.