Cobalt Oxide Materials Research Articles

Low-temperature hydrothermal synthesis of the three-layered sodium cobaltite P3-NaxCoO2 (x ∼ 0.60)

In order to obtain the layered sodium cobalt oxide materials by hydrothermal synthesis, the yield diagram for Na–Co–H2O system has been built and studied. In the same time, the well-known data of Co–H2O system have been extended at 250°C in basic solution.We had first synthesized directly the high temperature stable phase, P3-Na0.6CoO2 by a one-step low-temperature hydrothermal method. The rhombohedral structure of P3-Na0.6CoO2 has been determined by X-ray diffraction (XRD) and the purity of phases has been confirmed by XPS. The thermal stability of P3-Na0.6CoO2 has been investigated by means of high temperature X-ray diffraction in 298–873K range and when the temperature has reached 723K, the completely transformation of P3-Na0.6CoO2 in the rhombohedral stable phase α-NaCoO2 (space group R-3m) was observed. Also, a formation mechanism of P3-Na0.6CoO2 phase using the unit cell theory in the hydrothermal process was proposed.

Composition Optimization of Layered Lithium Nickel Manganese Cobalt Oxide Materials Synthesized via Ultrasonic Spray Pyrolysis

Lithium-rich, layered composites of xLi2MnO3·(1−x)Li(Ni1/3Mn1/3Co1/3)O2 were synthesized via spray pyrolysis to identify the chemistry yielding optimal electrochemical performance for materials produced by this method. The x values selected for optimization were x = 0.3, 0.5, 0.7, equivalent to Li1.14Mn0.46Ni0.2Co0.2O2, Li1.2Mn0.54Ni0.13Co0.13O2 and Li1.26Mn0.6Ni0.07Co0.07O2, respectively. The materials were annealed at 850°C or 900°C for 2 hours, and then tested in coin cells. Li1.2Mn0.54Ni0.13Co0.13O2 annealed at 900°C displayed the best electrochemical performance with excellent capacity retention, displaying a reversible capacity of 236 mAhg−1 after 100 cycles when cycled between 2.0–4.8 V at C/10 rate, where 1C = 280 mAg−1. The cycling profiles display voltage fade, presumably due to a layered-spinel phase transformation. The synthesis method leads to high purity and excellent uniformity at the nanoscale, and the materials have less voltage fade compared to similar materials produced by co-precipitation. Voltage fade is more pronounced when the upper cut-off voltage is 4.8 V, as opposed to 4.6 V. A decrease in the Li2MnO3 content of the material reduces voltage fade, such that x = 0.3 (or Li1.14Mn0.46Ni0.2Co0.2O2) shows the best structural stability over cycling.

Characteristics of wet and dry crushing methods in the recycling process of spent lithium-ion batteries

Methods of wet and dry crushing are adopted to experiment on spent lithium-ion batteries in this investigation. Particle size distribution is analyzed using the wet and dry screening respectively and fine crushed products are characterized by XRD, SEM and EDX. A comprehensive comparison of the characteristics between the two crushing methods indicates that the wet crushing results in an enrichment of each component in spent lithium-ion batteries to fine fractions because of the scouring action of water flow, which makes the fine products complicated and lost; while the dry crushing method can bring the selective crushing characteristics of spent lithium-ion batteries into full play, and in this case, lithium cobalt oxide and graphite electrode materials can be liberated from aluminum foil and copper foil without the overcrushing of the other components in spent lithium-ion batteries. Thus, the purity and dispersion of electrode materials can be improved to create favorable conditions for subsequent purification and regeneration.

The Nature of Lithium Battery Materials under Oxygen Evolution Reaction Conditions

Transition-metal oxide and phosphate materials, commonly used for lithium battery devices, are active as oxygen evolution reaction (OER) catalysts under alkaline and neutral solution conditions. Electrodes composed of LiCoO(2) and LiCoPO(4) exhibit progressive deactivation and activation for OER catalysis, respectively, upon potential cycling at neutral pH. The deactivation of LiCoO(2) and activation of LiCoPO(4) are coincident with changes in surface morphology and composition giving rise to spinel-like and amorphous surface structures, respectively. The amorphous surface structure of the activated LiCoPO(4) is compositionally similar to that obtained from the electrodeposition of cobalt oxide materials from phosphate-buffered electrolyte solutions. These results highlight the importance of a combined structural and electrochemical analysis of the materials surface when assessing the true nature of the OER catalyst.

Reversible control of the electronic density of states at the Fermi level of Ca3Co4O9+δ misfit-layered oxide single crystals through O+/H+ plasma exposure

Misfit-layered Ca3Co4O9 crystals were grown and characterized via XRD, SEM, and photo-emission spectroscopy (PES). The evolution of the intensity at the Fermi level (E F) with varying oxygen content was studied by PES. Oxygen species were successfully introduced and removed through O+ and H+ microwave-plasma (2.45 GHz, 2–5 mbar) treatments, respectively. A 5 min O+ plasma exposure was observed to result into a drastic enhancement in the E F intensity, demonstrating the influence of oxygen content to the charge carrier population in layered cobalt-oxide materials.

ChemInform Abstract: Standard Enthalpy of Formation of NaxCoO2 System

Abstract[solution calorimetric determination for x = 0.1, 0.2, ...

Standard enthalpy of formation of NaxCoO2 system

Layered sodium cobalt oxide (NaxCoO2) materials have attracted lot of attention in recent times because of their large thermoelectric power. Information on thermodynamic properties is necessary to predict the stability of these compounds. The present study deals with determination of enthalpy of formation of sodium-cobalt oxides [NaxCoO2 (x=0.1, 0.2…0.9)] using a solution calorimeter. The standard molar heat of dissolutions of NaxCoO2 (x=0.1, 0.2…0.9), NaCl(s), CoCl3(s) and H2O (l) in 0.150dm3 (1:1 ratio) aqueous HCl solution of concentration 5.96moldm−3 were measured by an isoperibol solution calorimeter. Using the values of the measured enthalpy of dissolution and other auxiliary data, the standard molar enthalpies of formation (ΔfHm°298) of the compounds were determined. The values of ΔfHm°298 for the Na0.1CoO2(s), Na0.2CoO2(s), Na0.3CoO2(s), Na0.4CoO2(s), Na0.5CoO2(s), Na0.6CoO2(s), Na0.7CoO2(s), Na0.8CoO2(s) and Na0.9CoO2(s) compounds are found to be −(598.61±6.03), −(637.40±6.04), −(676.26±6.04), −(716.53±6.05), −(758.03±6.06), −(800.04±6.07), −(841.58±6.08), −(883.38±6.09), −(924.93±6.10)kJmol−1, respectively.

Synthesis and characterization of manganese oxide and cobalt oxide nano-structure

The preparation of nanostructure type manganese oxide and cobalt oxide materials with the smallest particle size is reported here. The nanorod manganese oxide and cobalt oxide nanotube were prepared via a sol-gel reaction in reverse micelles from KMnO4 and CoCl2 with respectively source at room-temperature. The structure and surface morphology of the obtained manganese oxide were studied by means of X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and transmission electron microscopy.

Tunable interconnectivity of mesostructured cobalt oxide materials for sensing applications

A mesostructured cobalt oxide microsensor was fabricated using a template replication method under different hydrothermal treatments, and attempts were made to enhance the response of this gas sensor. To evaluate the sensing performance, the sensing materials were deposited via the dielectrophoresis (DEP) process, on micro-hot-plate platforms with interdigitated electrodes. The resistance changed when the carbon monoxide target gas was injected at the optimum temperature. The mesostructured cobalt oxide material with high hydrothermal treatment revealed the well-ordered domains, whereas with low hydrothermal treatment it did not contain ordered domains. Moreover, the cobalt oxide high hydrothermal material had 1.5 times the response to 70 ppm carbon monoxide as the low hydrothermal treatment sample. The unobstructed interconnectivity promotes gas diffusion and increases the active surface areas.

The highly active catalysts of nanometric CeO2-supported cobalt oxides for soot combustion

Nanometric CeO2-supported cobalt oxide materials with variable Co/Ce atomic ratios were prepared by the method of ultrasonic-assisted incipient-wetness impregnation. The catalytic behaviors of a series of CoOx/nmCeO2 catalysts have been studied for soot combustion. XRD, XPS, Raman, UV–vis DRS and FT-IR spectroscopy characterization results indicated that CoO or cobalt–cerium solid solutions were formed in the samples with the low Co loading amount, while Co3O4 was formed in the samples with high Co loading amount. CoOx/nmCeO2 catalysts can further promote soot combustion in contrast to nanometric CeO2. This improvement is related to the increase in the redox properties of the catalysts brought about by loading cobalt oxide on nanometric CeO2. The TPR experiment results under hydrogen atmosphere indicated that the presence of Co decreases the reduction temperature of catalyst from 555°C (nanometric CeO2) to 286°C (Co20/nmCeO2). On the other hand, attributing to nanoparticle effect and NO2 formation, Com/nmCeO2 oxide catalysts prepared in this study have very high activity for soot combustion. The best catalytic activity was obtained over Co20/nmCeO2 catalyst that T10, T50, T90 were 286°C, 368°C, 418°C, respectively, and SCO2m was 98.8%. Compared with the blank case (i.e., without catalyst) for soot combustion, T50 decreased by more than 200°C and SCO2m increased by 40% point. And this catalytic activity for the combustion of soot particle is as good as supported Pt catalysts, which is the best catalyst system so far reported for soot combustion under loose contact conditions. This temperature of soot combustion can ensure immediate activation of the catalyst on the filter under the conditions of diesel engine emissions.

Structural and electrochemical investigation of LiNi0.8Co0.2 − x M x O2 (M = Al, Al+Mg, Al+Mg+Fe) synthesized by solid-state method

Lithium nickel cobalt oxide materials doped with Al, Mg, and Fe were synthesized by solid-state reaction at 800 °C for 18 h to study the effects of adding transition and nontransition metals to the structure. Crystalline compounds were obtained as revealed by powder X-ray diffraction (XRD). Energy dispersive analysis of X-rays (EDAX) was used to determine the elemental ratio of all the samples. Impedance measurements showed that all samples have decreasing conductivities at higher temperatures and gave negative activation energies. The addition of nontransition metals actually decreased the conductivities of the materials.

Synthesis and Structural Characterization of a New Heterobimetallic Coordination Complex of Barium and Cobalt for Use as a Precursor for Chemical Vapor Deposition

Ba(dmae)2 (dmaeH=N,N-dimethylaminoethanol, C4H11NO) reacts with Co(acac)2 (acac=2,4-pentanedionate) to produce the trinuclear coordination complex [Ba2Co(acac)4(dmae)3(dmaeH)] in an 85% yield. Spectroscopic and single-crystal X-ray diffraction experiments indicate that the complex possesses a structure in which two barium atoms and a cobalt atom are bridged by acac and dmae groups. The barium centers are eight and nine coordinate with BaO7N and BaO7N2 coordination spheres while the cobalt is a more regular CoO5N octahedron. This 2:1 heterobimetallic molecular complex was investigated as precursor for the deposition of thin film by AACVD. The film was characterized by SEM and XRD. TGA shows that the complex starts thermal decomposition upon heating in nitrogen atmosphere at 105 degrees C to produce barium cobalt oxide material of a Ba2CoO3 composition with an orthorhombic structure. The synthetic approach detailed here represents a unique route to the formation of a heterobimetallic barium cobalt coordination complex.

Moisture-uptake by the positive active material from the casting solvent and the ambient environment

It is widely recognized that the presence of residual moisture has significant detrimental effects on the performance of lithium ion batteries. Studies have shown that the positive active material can be a major source of moisture contributors to the overall cell moisture. The aim of the present study is to understand the factors affecting moisture uptake by the doped-lithium nickel cobalt oxide material from the casting solvent, acetone, and the ambient environment. As-is and the air-dried powders under various conditions (300 °C for 24 h, 500 °C for 8 h, and 500 °C for 24 h) were exposed to ambient and humid air for various lengths of time. Similarly, all these powders were exposed to extra dry (47 ppm) and wet (5789 ppm) acetone. Karl Fisher measurements at 160 °C and 290 °C show that humidity levels (80–85% relative humidity versus 20–25%) and the exposure times are the critical factors. Acetone wetness and the length of exposure in it do not contribute significantly to the moisture uptake by the active material. Cathode powder drying helps in minimizing the amount of moisture uptake from the environment.

Ｘ線回折法および第一原理計算法による無機結晶の結晶構造および電子構造に関する研究

Crystal structures and electron density distributions of some manganese and cobalt oxide materials have been studied by the maximum entropy method using single-crystal X-ray diffraction data measured at room temperature. The nature of chemical bonding in these oxides is understood from the present structural and electron density analyses. The features of electron density distribution obtained theoretically by FLAPW calculations for these oxides were in good agreement with the present experimental observations.