One‐Pot Synthesis of 1,4‐Dihydro‐2‐thioxo‐2H‐3,1‐benzoxazine‐4‐acetic Acid Derivatives by the Reaction of 2‐Isothiocyanatophenyl Ketones with Lithium Enolates of Acetates and Tertiary Acetamides

The one‐pot synthesis of 4‐aryl‐1,4‐dihydro‐2‐thioxo‐2H‐3,1‐benzoxazine‐4‐acetic acid derivatives 2 was achieved in good yields by the reaction of aryl(2‐isothiocyanatophenyl)methanones 1 with lithium enolates of acetates and tertiary acetamides. (2E)‐1‐(2‐Isothiocyanatophenyl)‐3‐phenylprop‐2‐en‐1‐one ( 3 ) gave 1,4‐dihydro‐4‐[(1E)‐2‐phenylethenyl]‐2‐thioxo‐2H‐3,1‐benzoxazine‐4‐acetic acid derivatives 4 in good yields as well.     

Ordered tetragonal spinel LiMnNbO4 prepared in reducing atmosphere

LiMnNbO₄, the first quaternary compound in Li-Mn-Nb-O system, has been prepared by solid-state reaction in hydrogen atmosphere at 1050 °C. According to the X-ray Rietveld refinement results (R(F²)=0.0265, χ²=2.765), it is isostructural with LiZnNbO₄: tetragonal, P4₃22, a=6.1858(1), c=8.5312(1) Å, Z=4, spinel-derived, with Li and Nb ordered on octahedral sites and with Mn in tetrahedral coordination.     

Structural and vibrational study a new potassium lithium dihydrogenphosphate KLi(H2PO4)2

The single crystal of potassium lithium dihydrogenphosphate KLi(H₂PO₄)₂ (notated as KLDP) was synthesized at room temperature and its structure determined by single crystal X-ray diffraction. The compound was found to crystallize in the monoclinic system with space group P2₁/c (No.14) and the following parameters a = 7.5197(6), b = 12.8943(10) and c = 7.3900(6) Å, β = 98.477(3) °, Z = 4. This feature structure consists of LiO₄ tetrahedra linked by corners with H₂PO₄ groups to form infinite layer running along the ab plane. In the interlayer, KO₈ polyhedra form layers parallel to the same plane. In addition, Raman and infrared spectra were measured at room temperature, which confirm the presence of H₂PO₄, LiO₄ groups and ABC bands in the unit cell. In fact, these fundamental vibrations were proposed by analogy with spectra of other phosphate-based hydrogen-bonded compounds.     

From a 3D protonic conductor VO(H2PO4)2 to a 2D cationic conductor Li4VO(PO4)2 through lithium exchange

A new phase, Li₄VO(PO₄)₂ was synthesized by a lithium ion exchange reaction from protonic phase, VO(H₂PO₄)₂. The structure was determined from neutron and synchrotron powder diffraction data. The exchange of lithium causes a stress, leading to a change in the dimensionality of the structure from 3D to 2D by the displacement of oxygen atoms. Thus, Li₄VO(PO₄)₂ crystallizes in P4/n space group with lattice parameters a=8.8204(1) Å and c=8.7614(2) Å. It consists of double layers [V₂P₄O₁₈]_∞ formed by successive chains of VO₆ octahedra and VO₅ pyramids with isolated PO₄ tetrahedra. The lithium ions located in between the layers promote mobility. Furthermore, the ionic conductivity of 10⁻⁴ S/cm at 550 °C for Li₄VO(PO₄)₂ confirms the mobility of lithium ions in the layers. On the other hand, VO(H₂PO₄)₂ exhibits a conductivity of 10⁻⁴ S/cm at room temperature due to the presence of protons in tunnels.     

Synthesis and electrochemical performances of Li1+ y Mn2− y O4 powders of well-defined morphology

The spinel phases Li_{1+ y} Mn_{2− y} O₄ have been synthesized by a novel synthesis method that presents advantages compared to the classical ceramic method, namely, in terms of preparation time, costs and electrochemical performances of the resulting products. This consists of a two-stage process. First, two precursor phases (Li-EG and Mn-EG) are synthesized by reacting powdered lithium hydroxide and electrolytic manganese dioxide (EMD) in ethylene glycol (EG) under reflux, respectively. Secondly, the precursor products are mixed and heat treated under air, following various heating sequences, to produce electrochemically active Li_{1+ y} Mn_{2− y} O₄ powders of well-defined morphology. Once the synthesis parameters involved in these two steps are controlled, the obtained Li_{1+ y} Mn_{2- y} O₄ powders exhibit electrochemical performances that compare favorably with those observed in the case of the high-temperature (HT) Li_{1+ y} Mn_{2− y} O₄ made by the ceramic route, both in terms of reversible/irreversible capacities and cycling behavior at 25 °C and 55 °C. Received: 12 August 1997 / Accepted: 20 October 1997     

Synthesis and structures of the 2-(dimethylsila)pyrimidine derivatives (Ar = Ph, C6H4Bu-4; X = H, SiMe3, Li(hmpa)2, K(thf)3; n = 1, 2)

Five crystalline 2-(dimethylsila)pyrimidine derivatives (Z) have been prepared in excellent 1–4 or satisfactory 5 yield and characterised. The source of each was ultimately Li[CH(SiMe₂R)(SiMe₂OMe)] [R = Me (B) or OMe (I)]. Compound 1 (Z with Ar = Ph, X = SiMe₃, n = 1) was obtained from Z [with Ar = Ph, X = Li(OEt₂), n = 4; previously isolated from B [P.B. Hitchcock, M.F. Lappert, X.-H. Wei, J. Organomet. Chem. 689 (2004) 1342]] and Me₃SiCl. The potassium salt 2 [Z with Ar = C₆H₄Bu^t-4; X = K(thf)₃, n = 2] was made from K[CH(SiMe₃)(SiMe₂OMe)] (C) (via B) and 4-Bu^tC₆H₄CN. Treatment of 2 with 1,2-dibromoethane afforded 3 (Z with Ar = 4-Bu^tC₆H₄; X = H, n = 1); which when reacted with successively n-butyllithium and Me₃SiCl produced 4 (Z with Ar = 4-Bu^tC₆H₄, X = SiMe₃, n = 1). Compound 5 [Z with Ar = 4-Bu^tC₆H₄, X = Li(hmpa)₂, n = 1] resulted from I with 4-Bu^tC₆H₄CN and then OP(NMe₂)₃ (≡ hmpa). Plausible reaction pathways from the appropriate alkali metal alkyl C or I to 2 or 5, respectively, are suggested; these involve regiospecific 1,3-migrations of SiMe₂OMe from C → N and electrocyclic loss of Me₃SiOMe or SiMe₂(OMe)₂, respectively. The X-ray structures of crystalline 1, 2 and 5 are presented.     

Effect of the ZnNi y Mn2– y O4 (0 ≤ y ≤ 1) spinel composition on electrochemical lithium insertion

The electrochemical insertion of lithium in the spinel-type manganite with the formula ZnNi _y Mn_{2– y} O₄ has been studied. The galvanostatic discharge curves show that the best performance is obtained for y = 0.25, where a tetragonal to cubic structural transformation occurs. The thermodynamics and kinetics of the process of insertion of the lithium into the tetragonal spinel Li _x ZnNi_0.25Mn_1.75O₄ (x = 0.05–1.3) have been studied. The molar thermodynamic quantities, such as enthalpy, entropy and free energy determined by EMF-T measurements, varied with the lithium concentration in the oxide structure, and a major variation was observed around x = 0.8. The chemical diffusion coefficient of lithium in these spinels was also determined. Structural analysis, degree of oxidation and magnetic susceptibility measurements were carried out for the lithiated oxides in order to obtain the cationic distribution as a function of x. It has been possible to demonstrate that, upon lithium insertion, Mn⁴⁺ ions on B sites are reduced to Mn³⁺ and then to Mn²⁺. A cooperative Jahn-Teller effect is present in these spinel manganese-nickel oxides. Received: 4 February 1997 / Accepted: 11 April 1997     

High-temperature combustion synthesis and electrochemical characterization of LiNiO2, LiCoO2 and LiMn2O4 for lithium-ion secondary batteries

Lithium nickelate (Li_0.88Ni_1.12O₂), lithium cobaltate (LiCoO₂) and lithium manganate (LiMn₂O₄) were synthesized by fast self-propagating high-temperature combustion and their phase purity and composition were characterized by X-ray diffraction and inductively coupled plasma spectroscopy. The electrochemical behaviour of these oxides was investigated with regard to potential use as cathode materials in lithium-ion secondary batteries. The cyclic voltammograms of these cathode materials recorded in 1 M LiClO₄ in propylene carbonate at scan rates of 0.1 and 0.01 mV s^–1 showed a single set of redox peaks. Charge-discharge capacities of these materials were calculated from the cyclic voltammograms at different scan rates. The highest discharge capacity was observed in the case of Li_0.88Ni_1.12O₂. In all the cases, at a very slow scan rate (0.01 mV s^–1) the capacity of the charging (oxidation) process was higher than the discharging (reduction) process. A strong influence of current density on the charge-discharge capacity was observed during galvanostatic cycling of Li_0.88Ni_1.12O₂ and LiMn₂O₄ cathode materials. LiMn₂O₄ can be used as cathode material even at higher current densities (1.0 mA cm^–2), whereas in the case of Li_0.88Ni_1.12O₂ a useful capacity was found only at lower current density (0.2 mA cm^–2). For the fast estimation of the cycling behaviour of LiMn₂O₄, a screening method was used employing a simple technique for immobilizing microparticles on an electrode surface. Electronic Publication     

Synthesis of (4Z)‐4‐(Arylmethylidene)‐5‐ethoxy‐1,3‐oxazolidine‐2‐thiones by the Reaction of Ethyl (2Z)‐3‐Aryl‐2‐isothiocyanatoprop‐2‐enoates with Organolithium Compounds

A convenient one‐pot method for the preparation of (4Z)‐4‐(arylmethylidene)‐5‐ethoxy‐1,3‐oxazolidine‐2‐thiones 2 and 3 from ethyl (2Z)‐3‐aryl‐2‐isothiocyanatoprop‐2‐enoates 1 , which can be easily prepared from ethyl 2‐azidoacetate and aromatic aldehydes, has been developed. Thus, these α‐isothiocyanato α,β‐unsaturated esters were treated with organolithium compounds, including lithium enolates of acetates, to provide 5‐substituted (4Z)‐4‐(arylmethylidene)‐5‐ethoxy‐1,3‐oxazolidine‐2‐thiones, 2 , and 2‐[(4Z)‐(4‐arylmethylidene)‐5‐ethoxy‐2‐thioxo‐1,3‐oxazolidin‐5‐yl]acetates, 3 .     

Electrochemical Performance of LiMn2O4/LiFePO4 Blend Cathodes for Lithium Ion Batteries

A series of LiMn₂O₄/LiFePO₄ blend cathodes was prepared by hand milling and ball milling in order to compensate the disadvantage of spinel LiMn₂O₄ and olivine LiFePO₄. The morphologies of the blends were studied by scanning electron microscopy, and their electrochemical properties were studied by charge-discharge cycling, cyclic voltammetry and electrochemical impedance spectroscopy. It is easy to obtain uniform LiMn₂O₄/LiFePO₄ blends by the hand milling technique, while significant particle agglomeration is caused by the ball milling technique. When the LiMn₂O₄:LiFePO₄ mass ratio is 1:1, the nano-sized LiFePO₄ powders not only uniformly cover the micron-sized LiMn₂O₄ particles but also effectively fill in the cavities of the LiMn₂O₄ space. Such morphology offers a good electrical contact and a high tap density, which leads to a high discharge capacity and good cycle stability.     

Synthesis of aminopyridines from 2-fluoropyridine and lithium amides

Lithium amides promote the amination of 2-fluoropyridine under mild reaction conditions, providing 2-aminopyridines in good yields and purity. Treatment of 2-fluoropyridine with 1 equiv of lithium amide at room temperature affords complete conversion after 2 h. To our knowledge, this is the first study of lithium amide-promoted amination of fluoropyridines that are not further activated by electron-withdrawing groups.     

LiLa2F3(SO4)2 und LiEr2F3(SO4)2: Fluoridsulfate der Selten‐Erd‐Elemente mit Lithium

LiLa₂F₃(SO₄)₂ and LiEr₂F₃(SO₄)₂: Fluoride‐Sulfates of the Rare‐Earth Elements with Lithium The reaction of LiF with the anhydrous sulfates M₂(SO₄)₃ (M = La, Er) in sealed gold ampoules yields single crystals of the pseudo quaternary compounds LiLa₂F₃(SO₄)₂ and LiEr₂F₃(SO₄)₂. According to X‐ray single crystal investigations, LiLa₂F₃(SO₄)₂ crystallizes with the monoclinic (I2/a, Z = 4, a = 828.3(2), b = 694.7(1), c = 1420.9(3) pm, β = 95.30(2)°, R_all = 0.0214) and LiEr₂F₃(SO₄)₂ with the orthorhombic crystal system (Pbcn, a = 1479.1(2), b = 633.6(1), c = 813.7(1) pm, R_all = 0.0229). A common feature of both structures is a dimeric unit of metal atoms connected via three fluoride ions. This leads to relatively short metal‐metal distances (La³⁺–La³⁺: 389 pm, Er³⁺–Er³⁺: 355 pm). In LiLa₂F₃(SO₄)₂, Li⁺ is surrounded by four oxygen atoms of four sulfate groups and one fluoride ion in form of a trigonal bipyramid, in LiEr₂F₃(SO₄)₂ two further fluoride ligands are attached.     

非均匀成核法表面包覆氧化铝的尖晶石LiMn2O4研究

采用高温固相法合成尖晶石LiMn2O4,以非均匀成核方式对其进行包覆氧化铝的表面处理.通过XRD、SEM、粒度分析等技术对表面处理前后的LiMn2O4进行表征,分析了表面处理前后LiMn2O4物理特性的变化,并结合电化学性能测试,研究了表面处理工艺对LiMn2O4电化学容量与循环性能的影响.未经表面处理的LiMn2O4在1 C倍率下初期放电容量为86.5 mA•h•g－1,50次循环充放电后容量衰减26.3％.表面包覆0.5％、1％(w)氧化铝的LiMn2O4在1 C倍率下的初期放电容量分别为96.0、80.1 mA•h•g－1,经过50次循环后,容量分别降低7.0％、5.6％.实验结果表明,表面处理后的LiMn2O4循环性能显著提高,而且随着氧化物含量的增加,循环性能增强,但放电容量降低.     

Nanocrystalline ZnMn2O4 as a novel lithium-storage material

Nanocrystalline ZnMn₂O₄ is prepared by a polymer-pyrolysis route and used as a novel anode for lithium ion batteries. XRD and HRTEM studies reveal that the products are highly phase-pure and 30–60 nm in size. Galvanostatic cycling of ZnMn₂O₄ electrode at 100 mA g⁻¹ (about 0.52 mA cm⁻²) between 0.01 and 3.0 V up to 50 cycles exhibits almost stable cycling performance between 10 and 50 cycles with only an average capacity fade of 0.20% per cycle and the electrode still maintains a capacity of 569 mAh g⁻¹ after 50 cycles.     

A novel synthesis of 4-propyl-2H-1-benzopyran-2-ones

Reaction of 2-hydroxybutyrophenones1–5 with ethoxycarbonylmethylenetriphenylphosphorane furnishes the 4-propyl-2H-1-benzopyran-2-ones6–10.

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Eine neue Synthese von 4-Propyl-2H-1-benzopyran-2-onen

Zusammenfassung Die Reaktion von 2-Hydroxybutyrophenonen1–5 ergab mit Ethoxycarbonylmethylentriphenylphosphoran die 4-Propyl-2H-1-benzopyran-2-one6–10

     

Synthesis of 4-amino-substituted but-2-en-4-olides

Previously unknown 4-amino derivatives of spiro-annelated Δ²-butenolide were synthesized by the addition of various amines at the activated triple bond of 4-hydroxy-2-alkynoic esters. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2761–2770, December, 2005.     

Electrochemical properties of LiMn2O4 films produced by combustion reaction

Lithium manganese oxide powders were prepared via combustion reaction. Structural characterization of the powder using X-ray diffraction and scanning electron microscopy confirmed the formation of a LiMn₂O₄ nanosized powder. LiMn₂O₄ films were prepared by spin coating using 80 wt% of oxide, 15 wt% of polyaniline (PAni) as an electronic conductor and 5 wt% of polyvinylidene (PVDF) as a binder in N.N.-dimethyl acetamide. A Coulombic efficiency of 96% confirmed the electrochemical stability of the composite. The variation in impedance as a function of the lithium intercalation/deintercalation process reflected the interaction between the oxide and/or polyaniline particles at a high frequency range, and a diffusion tendency was observed at medium and low frequency ranges. The capacity values of the composite electrodes relative to the LiMn₂O₄ mass were 178.6/177.5 and 145/140 mAh g⁻¹ for the first and 25th charge/discharge cycles, respectively.     

锂离子电池正极材料锰酸锂合成的动力学

用DTA和XRD方法研究空气气氛中合成锰酸锂的反应过程，利用Doyle-Ozawa法和Kissinger法计算出各反应阶段的表观活化能，依次为66.3、72.6 、128.1和113.9 kJ•mol－1.用Kissinger法确定每个反应阶段的反应级数、频率因子和动力学方程.由LiOH•H2O和MnO2合成尖晶石型锰酸锂的动力学，可为制备锰酸锂提供理论依据. XRD、SEM和粒度分析表明，理论优化工艺后合成的LiMn2O4物相纯净，形貌规整，颗粒分布均匀.     

锂离子电池正极材料LiMn2-xCrxO4电化学性能的研究

针对尖晶石型LiMn2O4锂离子电池正极材料的容量衰减,提出了相应的抑制方法,所合成的LiMn2-xCrxO4(0相似文献   

Electrical conductivity studies in the system Li<Subscript>2</Subscript>TiO<Subscript>3</Subscript>-Li<Subscript>1.33</Subscript>Ti<Subscript>1.67</Subscript>O<Subscript>4</Subscript>

Electrical conductivity in the monoclinic Li₂TiO₃, cubic Li_1.33Ti_1.67O₄, and in their mixture has been studied by impedance spectroscopy in the temperature range 20–730 °C. Li₂TiO₃ shows low lithium ion conductivity, σ₃₀₀≈10^–6 S/cm at 300 °C, whereas Li_1.33Ti_1.67O₄ has 3×10^–8 at 20 °C and 3×10^–4 S/cm at 300 °C. Structural properties are used to discuss the observed conductivity features. The conductivity dependences on temperature in the coordinates of 1000/T versus log_e(σT) are not linear, as the conductivity mechanism changes. Extrinsic and intrinsic conductivity regions are observed. The change in the conductivity mechanism in Li₂TiO₃ at around 500–600 °C is observed and considered as an effect of the first-order phase transition, not reported before. Formation of solid solutions of Li_{2– x} Ti_{1+ x} O₃ above 900 °C significantly increases the conductivity. Irradiation by high-energy (5 MeV) electrons causes defects and the conductivity in Li₂TiO₃ increases exponentially. A dose of 144 MGy yields an increase in conductivity of about 100 times at room temperature. Electronic Publication