Alloy formation processes at electrochemical intercalation of lithium into intermetallic compounds of magnesium with zinc

A comparative study of alloy formation processes that occur during the electrochemical intercalation of lithium from lithium chloride solutions in dimethylformamide into intermetallic compounds of magnesium with zinc (MgZn₂, Mg₂Zn₃) and the corresponding individual metals is studied by chronopotentiometric and voltammetric methods. Lithium-containing phases are formed in all samples studied; moreover, for MgZn₂ and Mg₂Zn₃ electrodes, the phases formed are preferentially in the Li-Zn system. The largest number of lithium-containing phases is formed in zinc. It is shown that the electrochemical behavior of intermetallic electrodes is associated with their nature, where a single alloy component plays the key role, namely, zinc for MgZn₂ and magnesium for Mg₂Zn₃. The cathodic intercalation of lithium into MgZn₂ is characterized by anomalously low polarizability as compared with the other electrodes. The lithium extraction coefficient K _ex ^Li increases from the first to the tenth cycle for all electrode studied. The highest K _ex ^Li are typical of Zn and the lowest are typical of Mg₂Zn₃.     

Phase Formation and Kinetics of Electrochemical Intercalation of Lithium into Intermetallic Compounds MgCd and MgCd3

Electrochemical intercalation of lithium into intermetallic compounds (IMC) MgCd and MgCd₃ out of propylene carbonate solutions of LiBF₄ is studied. According to chronopotentiometry data, during the intercalation, lithium forms compounds with cadmium: Li₃Cd on MgCd or LiCd and Li₃Cd on MgCd₃. Reactions of solid-phase substitution, which occur on the electrodes, are accompanied by the destruction of initial IMC and generation of magnesium atoms. Chronoamperometry of MgCd–(Li) and MgCd₃–(Li) shows the lithium intercalation to be limited by nonstationary diffusion of lithium in the solid phase. The lithium diffusion in MgCd is slower and that in MgCd₃is faster than in Cd. The calculated potential dependences of the diffusion coefficient for lithium in MgCd and MgCd₃ are linear in semilogarithmic coordinates.     

Hydrogenation of fullerites in the presence of intermetallic compounds or metals

Fullerene hydrides containing 24–26 H atoms per fullerene molecule were obtained by hydrogenation of solid-phase mixtures of fullerenes with either intermetallic compounds LaNi₅, LaNi_4.65Mn_0.35, CeCo₃ or V and Pd metals with gaseous hydrogen at 1.0–2.5 MPa and 573–673 K. These fullerene hydrides decompose at 800 K with evolution of H₂. Upon subsequent heating to 1000 K, vanadium reacts with fullerene to yield a cubic phase of vanadium carbide. The intermetallic compounds react with fullerene with the formation of a metallic phase of the 3d-metal and destruction of fullerene. Palladium does not react with fullerene. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 679–683, April, 1997.     

Hydrides of intermetallic compounds with a H/M ratio greater than unity obtained at high hydrogen pressures

Novel hydride phases with H/M > 1 based on Zr₂Pd, Hf₂Pd, and Hf₂Cu (structures of the MoSi₂, type) have been synthesized at high H₂ pressures. The X-ray diffraction investigations of the resulting hydrides have been carried out. Some factors determining the maximum hydrogen content in the hydrides of intermetallic compounds are discussed. A model structure of the hydrides obtained is proposed, which assumes the possibility of direct H-H interactions when the interatomic distances are less than 1 Å.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 843–845, May, 1993.     

Metalation of 1-R-2-benzyl-o-carboranes with lithium aluminum hydride

Carboranes with the general formula I-R-2-PhCH₂-1,2-C₂B₁₀H₁₀ (R = Me, Prⁱ, Ph, PhCH₂) are readily metalated with lithium aluminum hydride in a THF solution at the CH₂ group. In this case only one hydrogen atom in LiAlH₄ is substituted, and trihydride complexes 1-R-2-PhCH(AlH₃Li)-1,2-C₂B₁₀H₁₀, are formed, which are stable in a solutionTranslated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1282–1284, May, 1996.     

Characterisation of four new two-dimensional lithium beryllofluoro-layered compounds

Four new amine-templated materials, containing two-dimensional lithium beryllofluoride sheets of the stoichiometry [LiBeF(4)](-), have been synthesised under hydrothermal and ambient pressure conditions. [LiBeF(4)][C(6)H(4)(CH(3))CH(2)NH(3)] (1), [LiBeF(4)][C(6)H(4)CH(2)NH(3)Cl] (2), [LiBeF(4)](2)[NH(3)CH(2)CH(2)CH(2)NH(3)] (3), and [LiBeF(4)][C(6)H(5)CH(2)CH(2)CH(2)NH(3)] (4) all contain well-separated anionic sheets containing two different topologies with the 'inter-layer' regions comprising of organoamine templating species. Use of the different organoamine templating agents results in compounds possessing very different relative arrangements of the lithium beryllofluoride sheets. The materials crystallise in P-centred orthorhombic and monoclinic cells; for 1 (templating agent: 3-methylbenzylamine) Pca2(1); for 2 (4-chlorobenzylamine) Pbca; for 3 (1,3-diamminopropane) Pccn, and for 4 (3-phenyl-1-propylamine) P2(1)/c. Hydrogen bonding exists between ions situated on the protonated amine groups on the templating species and electronegative fluoride ions, on MF(4) tetrahedra (where M=Li and Be).     

Dynamics of lithium electrode passivation in aprotic organic electrolytes,studied by electrochemical noise method

Lithium electrode passivation is studied in different organic electrolytes, namely, 1 M LiClO₄ in 1,3-dioxolane, 1 M LiN(CF₃SO₂)₂ in 1,3-dioxolane, 1 M LiPF₆ in an ethylene carbonate-diethyl carbonate mixture, 1 M LiPF₆ in an ethylene carbonate-dimethyl carbonate mixture, using the electrochemical noise method. The dynamics of passive film formation on the lithium surface in the mentioned electrolytes that differ in their corrosivity towards lithium is followed.     

Phase transformations in hydrogen sorption-desorption by hydrides of intermetallic compounds of the CrB structural type

State Institute of the Nitrogen Industry. M. V. Lomonosov State University, Moscow. Translated from Zhurnal Strukturnoi Khimii, Vol. 32, No. 5, pp. 74–81, September–October, 1991.     

Physicochemical and electrochemical properties of sulfolane solutions of lithium salts

The physicochemical and electrochemical properties (electrical conductivity, viscosity, density, and electrochemical stability) of sulfolane solutions of various lithium salts are studied. The nature of the anion considerably affects the physicochemical and electrochemical properties of the electrolyte systems considered. Sulfolane solutions of lithium salts have moderate electrical conductivity and high electrochemical stability, and can be used as electrolytes in lithium batteries.     

Valence state of hydrogen in hydrides of intermetallic compounds

The experimental data on the mechanism of hydride dispersion of intermetallic compounds of the LaNi₅ type and the crystal structures of hydride phases based on these compounds were analyzed. A new approach was suggested and substantiated, which allows one to consider hydride dispersion as a result of a redox process associated with the formation of H^δ− hydride ions at concentrations of hydrogen in the solid hydrideC _H>-C _{H cr}. The value ofC _{H cr} is determined by the redox potential of the reaction H^δ++M^δ−⇌H^δ′−+M^δ′+. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 214–217, February, 1998.     

Synthesis of carbon nanofibers by catalytic pyrolysis of ethylene and methane on hydrides of intermetallic compounds of lanthanum with nickel

Carbon nanofibers were synthesized by the pyrolysis of ethylene and methane on hydrides of intermetallides LaNi_nH_x (n = 2, 3, 5; x = 0.1–4). The influence of parameters of the synthesis (temperature and the ratio of gases in an Ar: H₂: C₂H₄ (CH₄) mixture) on the structure of nanofibers thus formed was studied. Hydrides of nickel intermetallides are more efficient catalytic systems than metallic nickel. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2210–2214, October, 2005.     

Effective extractants for the extraction of lithium from aqueous solutions containing sodium and potassium compounds

The extraction power of newly obtained pure methoxy-1,3-diketones in diluents and in their mixtures with electron-donating additives during the extraction of lithium from aqueous solutions containing sodium and potassium was investigated. High separation factors were obtained; no appreciable amounts of sodium and potassium were found in the extract after total extraction of the lithium.Institute of Chemical Kinetics and Combustion, Siberian Branch, Russian Academy of Sciences, 630090 Novosibirsk. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 6, pp. 1304–1310, June, 1992.     

Organoelement compounds in the electrochemical synthesis of fluoroorganics

Electrochemical generation of organic anion-radicals in the presence of fluoroorganosilanes causes the chain addition reaction. Adducts of CFCl₂SiMe₃, CFClCFSiMe₃ and CF₃SiMe₃ with benzaldehyde were obtained with conversion efficiency up to 8000%.Electroreduction of bis-(trifluoromethyl)mercury (II) was established to be the route for the intermediate formation of trifluoromethyl anion, which was trapped by the reactions with benzaldehyde, Me₃SiCl and bromobenzonitrile.The use of salen Ni(II) complex as mediator allows the electrochemical reduction of polyfluoroalkylchlorides at the potentials more than 1 V higher than their reduction potentials.     

锂电池电极过程的原位电化学原子力显微镜研究进展

随着人类对能源的使用与存储需求不断增加,高能量密度和高安全性能的二次锂电池体系正在被不断地开发与完善.深入理解充放电过程中锂电池内部电极/电解质界面的电化学过程以及微观反应机理,有利于指导电池材料的优化设计.原位电化学原子力显微镜将原子力显微镜的高分辨表界面分析优势与电化学反应装置相结合,能够在电池运行条件下实现对电极/电解质界面的原位可视化研究,并进一步从纳米尺度上揭示界面结构的演化规律与动力学过程.本文总结了原位电化学原子力显微镜在锂电池电极过程中的最新研究进展,主要包括基于转化型反应的正极过程、固体电解质中间相的动态演化以及固态电池界面演化与失效分析.     

无电沉积法AuNPs-MWCNTs的制备及其对黄酮类化合物的电化学催化性能研究

利用多壁碳纳米管具有较低的还原电位,以多壁碳纳米管作为还原剂和负载基底,通过无电沉积法制备了负载纳米金粒子的碳纳米管催化剂。此种材料具有更多的活性位点,避免了纳米金粒子表面保护剂的存在造成其催化活性降低的缺陷,发现其对典型黄酮类化合物-芦丁和黄芩苷具有良好的电化学催化性能和较高的灵敏度,并将其应用于电化学分析检测黄酮类化合物。     

锂离子电池负极材料铜锌锡硫纳米颗粒的制备及其电化学性能

以金属氯化物为金属源,硫脲为硫源,聚乙二醇和乙二醇为混合溶剂,采用溶剂热法一步合成了球形的铜锌锡硫纳米颗粒.利用X射线衍射仪(XRD),扫描电子显微镜(SEM)和透射电子显微镜(TEM)分析了铜锌锡硫纳米颗粒的物相、结构、形貌;利用电池测试系统对以铜锌锡硫纳米颗粒为锂离子电池负极材料组装的锂离子电池的电化学性能进行了测试.结果表明:所得到的产物为具有锌黄锡矿结构的纯相铜锌锡硫,颗粒直径在300～500nm.铜锌锡硫纳米颗粒作为锂离子电池的负极材料具有较好的稳定性,有望在锂离子电池研究和应用中得到推广.     

Dynamic electrochemical impedance spectroscopy of the adsorption and relaxation of polyaniline chains during potentiodynamic redox transformations

A new approach to an equivalent circuit analysis of impedance spectra of a conducting polyaniline (PAni) layer is presented. Film properties are often modeled by constant-phase elements (CPE), which are closer to experimental results than capacitors. We want to take an insight into the CPE. We propose a novel equivalent circuit based on the Frumkin-Melik-Gaikazyan adsorption model, as we suppose that the PAni layer molecules may behave like other adsorbing and relaxing organic compounds. Measurements are performed using recently developed experimental technique—dynamic electrochemical impedance spectroscopy. Obtained spectra are analyzed using the proposed equivalent circuits. Characteristics of several parameters are analyzed and discussed. Published in Russian in Elektrokhimiya, 2007, Vol. 43, No. 9, pp. 1111–1119. The text was submitted by the authors in English.     

The interaction of alkaline solutions of potassium borohydride with LaNi4.5M0.5 (M = Ni,Mn, Cr,Co, Fe,Cu, Al) intermetallic compounds

The behavior of LaNi_4.5M_0.5 (M = Ni, Mn, Cc Co, Fe, Cu, Al) interinctallic compounds (IMC) in alkaline solutions of KBH₄ (0.1; 1.0; 4.0 mol L^–1 KOH) Was investigated in the temperature range 298–318 K. The catalytic hydrolysis of KBH₄ is zero order with respect to KBH₄ and not order with respect to IMC. Activation energies of the catalytic hydrolysis of KBH₄ in the presence of' IMC are in the range of 60–65 U mol^–1. The rate of hydrolysis of KBH₄ increases with the concentration of the KOH solution. The hydrogenation of LaNi_4.5M_0.5 in alkaline solutions of KBH₄ yields -hybride phases for M = Min, Cr, Co, Cu, Al and -hybride phases for M = Ni, Fe.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1632–1635, July, 1996.     

Reactivity of lithium and barium carbonates with ZrO2:Y2O3 and Nasicon in solid state electrochemical gas sensors

The mutual reactivity in mixtures containing Nasicon (Na₃Zr₂Si₂PO₁₂) or YSZ (ZrO₂:Y₂O₃) solid electrolytes with Li₂CO₃ or Li₂CO₃:BaCO₃ sensing electrode materials was investigated using simultaneous DTA and TG and ex situ XRD techniques. The uncontrolled chemical reaction is suspected to be responsible for the instability of electrochemical gas sensors constructed from these materials. DTA and TG results obtained for Nasicon-carbonate mixtures indicate the possibility of reaction in the temperature range from about 470 to 650°C, which overlaps the sensor operating temperature range (300–525°C). The results obtained for YSZ-carbonate mixtures indicate that reaction between carbonate and the ZrO₂ takes place at higher temperatures and cannot explain the instability drift of investigated sensors. The mechanism of observed reactions in systems studied is also discussed. This revised version was published online in July 2006 with corrections to the Cover Date.