Lithium–manganese–nickel-oxide electrodes with integrated layered–spinel structures for lithium batteries

A series of lithium–manganese–nickel-oxide compositions that can be represented in three-component notation, xLi[Mn_1.5Ni_0.5]O₄ · (1 − x){Li₂MnO₃ · Li(Mn_0.5Ni_0.5)O₂}, in which a spinel component, Li[Mn_1.5Ni_0.5]O₄, and two layered components, Li₂MnO₃ and Li(Mn_0.5Ni_0.5)O₂, are structurally integrated in a highly complex manner, have been evaluated as electrodes in lithium cells for x = 1, 0.75, 0.50, 0.25 and 0. In this series of compounds, which is defined by the Li[Mn_1.5Ni_0.5]O₄–{Li₂MnO₃ · Li(Mn_0.5Ni_0.5)O₂} tie-line in the Li[Mn_1.5Ni_0.5]O₄–Li₂MnO₃–Li(Mn_0.5Ni_0.5)O₂ phase diagram, the Mn:Ni ratio in the spinel and the combined layered Li₂MnO₃ · Li(Mn_0.5Ni_0.5)O₂ components is always 3:1. Powder X-ray diffraction patterns of the end members and the electrochemical profiles of cells with these electrodes are consistent with those expected for the spinel Li[Mn_1.5Ni_0.5]O₄ (x = 1) and for ‘composite’ Li₂MnO₃ · Li(Mn_0.5Ni_0.5)O₂ layered electrode structures (x = 0). Electrodes with intermediate values of x exhibit both spinel and layered character and yield extremely high capacities, reaching more than 250 mA h/g with good cycling stability between 2.0 V and 4.95 V vs. Li° at a current rate of 0.1 mA/cm².     

Syntheses of organometallic monomers containing cobalt and manganese

Direct electrophilic substitution of the cyclopentadienyl ring of cymantrene has been used to prepare five cymantrenyl-monomers with unsaturated sidechains. Direct substitution of cymantrene with acryloyl- and methacryloyl chloride under Friedel-Crafts conditions has led to acryloyl- and methacryloylcymantrene. The complexes have been characterized using ¹H and ¹³C NMR, IR and elemental analysis. Both complexes polymerize under treatment with AIBN at 60–70°C. The chelated complex [n⁵-C₅H₄(CH₂CH=CH₂)]-Co[(NH)₂C₆H₄], was prepared from the treatment of [n⁵-C₅H₄(CH₂CH=CH₂)]Co(CO)₂ with I₂ followed by (NH)₂C₆H₄ and base. The complex was characterized with ¹H NMR and IR but failed to undergo free-radical polymerization. The strategies used to prepare organometallic polymers are discussed.     

Preparation and characterization of copper-doped cobalt oxide electrodes

Cobalt oxide (Co3O4) and copper-doped cobalt oxide (CuxCo(3-x)O4) films have been prepared onto titanium support by the thermal decomposition method. The electrodes have been characterized by different techniques such as cyclic voltammetry, scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy (XPS). The effect on the electrochemical and crystallographic properties and surface morphology of the amount of copper in the oxide layer has been analyzed. The XPS spectra correspond to a characteristic monophasic Cu-Co spinel oxides when x is below 1. However, when the copper content exceeds that for the stoichiometric CuCo2O4 spinel, a new CuO phase segregates at the surface. The analysis of the surface cation distribution indicates that Cu(II) has preference for octahedral sites.     

The effect of chromium substitution on the phase transition of lithium manganese spinel oxides

The phase transition of chromium substituted lithium manganese spinel oxide, LiCr_yMn_2−yO₄ was investigated by low-temperature powder X-ray diffractometry (XRD), differential scanning calorimetry (DSC), and electrical resistivity measurements. The sample prepared at 820 °C resulted in lowering the transition temperature T_t with Cr composition y, whereas T_t of the sample prepared at 750 °C remained constant for 0≤y≤0.17 in LiCr_yMn_2−yO₄. This would be caused by a difference in distribution of the substituted Cr³⁺ ion in octahedral site depending on the preparation temperature. The phase transition was suppressed with increasing the amount of Cr content.     

Lithium storage in single-walled carbon nanotubes

Here, we investigated the lithium insertion/extraction mechanism in single-walled carbon nanotubes (SWNTs) based both on the empty SWNTs and filled SWNTs, including ferrocene-filled SWNTs (Fc@SWNTs) and C₆₀-filled SWNTs (C₆₀@SWNTs). SWNTs, C₆₀@SWNTs and Fc@SWNTs were systematically investigated as anode materials for Li-ion batteries. The electrochemical performance of the C₆₀@SWNT electrode was slightly better than that of the SWNTs, and the reversible capacity of Fc@SWNTs per unit weight was ～1.7 times greater than that of the empty SWNTs due to its special tube internal structure. It was proved that the dominant reversible sites for lithium storage in empty SWNTs are the trigonal interstitial channels. Meanwhile, lithium can reversibly insert or extract the inner channels of the tubes after doping with ferrocene; the reversible capacity presented in the inner channels of Fc@SWNTs is about Li_1.13C₆.     

Determination of cobalt on surfactant-modified mercury electrodes

Cobalt ions can be determined in the presence of interfering matrix components such as zinc ions by applying adsorbed surfactants. The influence of different adsorption layers on the reduction processes of both ions was studied. Selective inhibition of the zinc signal was achieved even with an extremely large zinc(II) to cobalt(II) ratio in solutions such as zinc plating baths after modification of the mercury electrode with adsorbed tetrabutylammonium. The influence of additions of dimethylglyoxime and citrate and pH changes on the cobalt signal was investigated.     

Kinetic parameters of electroextraction of cobalt from aqueous solutions of cobalt and manganese sulfates

The effect exerted by cobalt(II) concentration in the initial solution and temperature on the kinetics of cobalt(II) electroextraction from cobalt(II) and manganese(II) sulfate solutions was studied. The kinetic parameters of the process were determined.     

Preparation of manganese oxide nanoparticles by thermal decomposition of nanostructured manganese carbonate

MnO and Mn₂O₃ nanoparticles were prepared in air and argon atmosphere by thermal decomposition of nanocrystalline manganese carbonate synthesized by reaction of manganese(II) nitrate with glycerol. Samples were characterized using transmission electron microscopy, simultaneous thermal analysis and X-ray diffraction analysis. Average sizes of prepared nanoparticles were calculated from XRD patterns using Scherrer equation. Also, the conditions for decomposition of manganese carbonate were optimized to obtain optimal nanoparticle sizes. Due to suitable sizes of prepared nanoparticles and the initial material, this method can be used in a wide range of industrial applications.     

EPR of divalent manganese in cobalt ammonium selenate hexahydrate

EPR of Mn²⁺ has been studied in cobalt ammonium selenate hexahydrate from ≈ 90 K to ≈ 300 K and the spin-hamiltonian parameters determined. It has been found that replacement of S by Se does not cause much change in the strength and symmetry of the crystal field at the divalent cation site in Tutton salts.     

Accumulation and voltammetric determination of cobalt at zeolite-modified electrodes

Chemically modified electrodes based on zeolite-containing graphite pastes were constructed and evaluated as sensor electrodes for the voltammetric determination of trace cobalt in solution. Zeolite molecular sieves with pore sizes of 3, 4, and 5 Å were all suitable for chemical deposition and subsequent voltammetric quantitation of trace Co(II). In order to cover a large range of parameters, the investigations were carried out using three zeolites (A, X, and Y), selected for their different cation-exchange capacities and ion-sieving properties. The analytical scheme, “preconcentration/voltammetric detection” for the determination of cobalt(II) species using zeolite-modified carbon paste electrodes (ZMCPE) was chosen. Compared to the corresponding unmodified electrodes, improvements in sensitivity were observed when using ZMCPEs due to analyte accumulation at the electrode’s surface by ion exchange in zeolite particles. The detection limit obtained for Co(II) was 3 ppm following 15 min of chemical deposition. A good correlation was found between the results obtained by ion exchange voltammetry and conventional ion-exchange characterization.     

Oxidation of electrodeposited cobalt electrodes in an alkaline electrolyte

The oxidation of electrodeposited Co electrodes has been studied in 0.1 M KOH_aq at potentials more negative than ?880 mV vs. Hg|HgO by means of electrochemical quartz crystal microbalance (EQCM) and rotating ring disk electrode coupled with cyclic voltammetry (CV) and chronoamperometry (CA). Dissolution of cobalt was found to be insignificant and does not constitute a step in the overall process of formation of the oxidised layer. The irreversibility of the oxidation process depends on the electrode potential and oxidation time. The composition of the oxidised layer depends on the oxidation potential: Co(OH)₂ is formed at more negative potentials, while at more positive potentials CoO is the prevailing product. The results obtained by means of three techniques (CV, CA and EQCM) reveal that at potentials not higher than ?880 mV, the oxidation of Co follows a direct logarithmic law. The mechanism of the process is discussed.     

波长色散X射线荧光光谱法测定钴精矿中钴、铜和锰含量

采用高纯氧化物经四硼酸锂和偏硼酸锂熔融制备人工标准样品,以氧化镱为内标,制作校准曲线,建立了波长色散型X射线荧光光谱法测定钴精矿中钴、铜、锰元素的分析方法。重点研究了混合熔剂、试样稀释比、氧化剂和内标选择、方法检出限、方法准确度和精密度等,结果表明,各元素校准曲线线性范围宽,相关系数均大于0.999, 钴、铜、锰元素检出限分别达到0.002%、0.001%和0.001%,测试准确度和精密度可靠,方法满足行业检测需求。     

Lithium insertion into manganese dioxide polymorphs in aqueous electrolytes

The electrochemical behaviour of the spinel-like LiMn₂O₄ was studied in non-aqueous and aqueous saturated alkali nitrate electrolytes in comparison with the layered manganese dioxide δ-MnO₂. The results obtained by galvanostatic and cyclic voltammetry techniques showed that the insertion of Li⁺/e^– or H⁺/e^– depends on both the host lattice and the type of electrolyte. The spinel-like LiMn₂O₄ preferably allowed the insertion of Li⁺/e^– in non-aqueous and aqueous saturated LiNO₃ electrolytes, as observed from the similarity of the electrochemical behaviour in these electrolytes and the stability of the structure. This was explained by the presence of a three-dimensional network of vacant tetrahedral and half-filled octahedral sites in LiMn₂O₄, which guarantee high mobility of Li⁺ ions. The layered manganese dioxide could be inserted by Li⁺/e^– only in non-aqueous electrolytes. The work described herein was carried out at the Institut für Anorganische und Analytische Chemie, Technische Universit?t Berlin, Germany     

Lithium storage in perovskite lithium lanthanum titanate

Perovskite lithium lanthanum titanate (LLTO) was synthesized using sol–gel method. It shows a reversible capacity of 145 mA h g^− 1 and moderate cycling performance between 0.01 and 2.00 V. Cyclic voltammetry and X-ray diffraction results demonstrate a two-step solid–solution reaction behavior in the voltage range of 0.00–3.00 V upon lithium insertion/extraction. A stable solid electrolyte interphase (SEI) layer is formed on the surface of LLTO after the initial discharge. Carbon coating by chemical vapor deposition improves its cycling performance significantly.     

The effect of manganese on the structural and surface properties of nanocrystalline cobalt catalyst for ammonia synthesis

Based on the active surface model of the iron catalyst for ammonia synthesis, the assumptions which led to obtaining the cobalt catalyst for ammonia synthesis were described. The incorporation into the system small amounts of manganese, an element which binds oxygen stronger than cobalt, has influence the development of the catalyst’s specific surface area. The activity of manganese modified catalysts is higher than that of cobalt catalyst without manganese addition. The obtained catalysts were characterized with the following methods: ICP-OES, XRD, BET      

Pyridine coordination to manganese(III) porphyrins: The effect of multiple functional substitution in porphyrin

To synthesize donor–acceptor complexes exhibiting biological activity, the reaction of (2,3,7,8,12,13,17,18-octaalkylporphinato)manganese(III) containing axial acetate and chloride ions with pyridine has been quantitatively studied. In all cases, equilibrium is established instantaneously to give 1 : 1 donor–acceptor complexes. The key spectral characteristics and stability parameters have been obtained for donor–acceptor dyads. Multiple functional substitution of the porphyrin macroheterocycle can be used to control the properties of porphyrins and dyads based on them.