Fe50Co50 nanoparticles via self-propagating high-temperature synthesis during milling

Self-propagating exothermic reactions during mechanical milling of FeCl₃/CoCl₂ mixture together with sodium seeds resulted in formation of Fe₅₀Co₅₀ nanoparticles. Highly exothermic reactions resulted in temperature raise and formation of Fe₅₀Co₅₀ phase within the first 5 min; however Fe₅₀Co₅₀ single-phase was obtained after 30 min of milling. The products were characterized by XRD, SEM, EDS, TEM and VSM. Obtained results showed that both milling time and NaCl salt matrix affected the size, morphology, microstructure and magnetic properties of the produced particles.     

Structural and magnetic properties of Co1−xZnxFe2O4 nanorods prepared by the solvothermal annealing method

Co_1−xZn_xFe₂O₄ (0.1≤x≤0.9) nanorods have been prepared by the thermal decomposition of the corresponding oxalate precursor, which was synthesized by the template-, surfactant-free solvothermal method. The as-prepared samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometry (VSM). The obtained Co_1−xZn_xFe₂O₄ (0.1≤x≤0.9) nanorods were built by many nanoparticles with average sizes around 20 nm to form one-dimensional arrays. Vibrating sample magnetometry measurements show that the coercivity of the ferrite nanorods decreases with increasing Zn content, whereas the specific saturation magnetization initially increases and then decreases with the increase of Zn content. The maximum saturation magnetization value of the as-prepared sample (Co_0.5Zn_0.5Fe₂O₄) reaches 43.0 emu g⁻¹.     

Influence of Pd on the structure and electrochemical hydrogen storage properties of Mg50Ti50 alloy prepared by ball milling

High-energy ball milling was used to modify the physico-chemical and the electrochemical hydrogenation properties of Mg₅₀Ti₅₀ alloy via the addition of Pd. This was done by first ball milling Mg and Ti together for (20 − x) hours. 3.3 at.% Pd was then added and ball milling was resumed for x hours. X-ray diffraction and X-ray photoelectron spectroscopy analyses revealed that the alloying of Pd with pre-milled Mg₅₀Ti₅₀ was initiated after only a few minutes and was completed after 5 h of milling. The maximum discharge capacity of the Mg₅₀Ti₅₀-3.3 at.% Pd electrode increased significantly with the milling time (from 35 mAh g⁻¹ for 5 min to 480 mAh g⁻¹ for 20 h of milling). The exchange current density increased with the milling time and was directly related to the Pd surface concentration, suggesting that Pd plays a key role in facilitating the charge-transfer reaction. In contrast, the incorporation of Pd had a minor effect on the hydrogen diffusion coefficient. The electrochemical pressure-composition isotherms revealed a significant destabilization of the hydride as the milling time with Pd increased. No significant improvement in the hydrogen storage properties of Mg₅₀Ti₅₀-Pd electrodes was observed for Pd concentrations higher than 3.3 at.%.     

Mechanosynthesis,crystal structure and magnetic characterization of M-type SrFe12O19

M-type strontium hexaferrite was prepared by mechanosynthesis using high-energy ball milling. The influence of milling parameters, hematite excess and annealing temperature on magnetic properties of SrFe₁₂O₁₉ were investigated. Commercial iron and strontium oxides were used as starting materials. It was found that mechanical milling followed by an annealing treatment at low temperature (700 °C) promotes the complete structural transformation to Sr-hexaferrite phase. For samples annealed at temperatures from 700 to 1000 °C, saturation magnetization values (M_s) are more sensitive to annealing temperature than coercivity values (H_c). The maximum M_s of 60 emu/g and H_c of 5.2 kOe were obtained in mixtures of powders milled for 5 h and subsequently annealed at 700 °C. An increase in the annealing temperature produces negligible changes in magnetic saturation and coercivity. An excess of hematite as a second phase produces a slight decrease in the saturation magnetization but leads to a significant increase in coercive field, reaching 6.6 kOe.     

Structural and electrical properties of La0.7Sr0.3Co0.5Fe0.5O3 powders synthesized by solid state reaction

This work investigates the effect of synthesis parameters (calcination temperature, milling conditions and sintering temperature) on the structural, morphological and electrical properties of La_0.7Sr_0.3Co_0.5Fe_0.5O₃ (LSCF) powders prepared by the solid state reaction. The thermogravimetric profile showed that the minimum temperature needed for the carbonate decomposition and formation of perovskite phase is 800 °C. SEM analysis revealed the loose and porous structure of the powder materials. The XRD patterns demonstrate that milling parameters such as grinding balls:sample ratio, rotational speed, and milling time influence the structural properties. The results revealed that powders synthesized with grinding balls:sample ratio of 8:1, 500 rpm and 4 h of milling present pure LSCF phase. Porosity of the pellets decreased with increasing sintering temperature from 950 to 1100 °C. Electrical conductivity was measured at 400–1000 °C and correlated with sintering temperature.     

Synthesis of LiNi0.9Co0.1O2 from Li2CO3, NiO or NiCO3, and CoCO3 or Co3O4 and their electrochemical properties

Cathode active materials with a composition of LiNi_0.9Co_0.1O₂ were synthesized by a solid-state reaction method at 850 °C using Li₂CO₃, NiO or NiCO₃, and CoCO₃ or Co₃O₄, as the sources of Li, Ni, and Co, respectively. Electrochemical properties, structure, and microstructure of the synthesized LiNi_0.9Co_0.1O₂ samples were analyzed. The curves of voltage vs. x in Li_xNi_0.9Co_0.1O₂ for the first charge–discharge and the intercalated and deintercalated Li quantity Δx were studied. The destruction of unstable 3b sites and phase transitions were discussed from the first and second charge–discharge curves of voltage vs. x in Li_xNi_0.9Co_0.1O₂. The LiNi_0.9Co_0.1O₂ sample synthesized from Li₂CO₃, NiO, and Co₃O₄ had the largest first discharge capacity (151 mA h/g), with a discharge capacity deterioration rate of −0.8 mA h/g/cycle (that is, a discharge capacity increasing 0.8 mA h/g per cycle).     

Solid solution between Al-ettringite and Fe-ettringite (Ca6[Al1 − xFex(OH)6]2(SO4)3·26H2O)

The solid solution between Al- and Fe-ettringite Ca₆[Al_1 − xFe_x(OH)₆]₂(SO₄)₃·26H₂O was investigated. Ettringite phases were synthesized at different Al/(Al + Fe)-ratios (= X_Al,total), so that X_Al increased from 0.0 to 1.0 in 0.1 unit steps. After 8 months of equilibration, the solid phases were analyzed by X-ray diffraction (XRD) and thermogravimetric analysis (TGA), while the aqueous solutions were analyzed by inductively coupled plasma optical emission spectroscopy (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS). XRD analyses of the solid phases indicated the existence of a miscibility gap between X_Al,total = 0.3-0.6. Some of the XRD reflections showed two overlapping peaks at these molar ratios. The composition of the aqueous solutions, however, would have been in agreement with both, the existence of a miscibility gap or a continuous solid solution between Al- and Fe-ettringite, based on thermodynamic modeling, simulating the experimental conditions.     

Effects of surface modification on the cycling stability of LiNi0.8Co0.2O2 electrodes by CeO2 coating

A high-performance LiNi_0.8Co_0.2O₂ cathode was successfully fabricated by a sol-gel coating of CeO₂ to the surface of the LiNi_0.8Co_0.2O₂ powder and subsequent heat treatment at 700 °C for 5 h. The surface-modified and pristine LiNi_0.8Co_0.2O₂ powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), slow rate cyclic voltammogram (CV), and differential scanning calorimetry (DSC). Unlike pristine LiNi_0.8Co_0.2O₂, the CeO₂-coated LiNi_0.8Co_0.2O₂ cathode exhibits no decrease in its original specific capacity of 182 mAh/g (versus lithium metal) and excellent capacity retention (95% of its initial capacity) between 4.5 and 2.8 V after 55 cycles. The results indicate that the surface treatment should be an effective way to improve the comprehensive properties of the cathode materials for lithium ion batteries.     

Study on phase structure and electrochemical properties of Ml1−xMgxNi2.80Co0.50Mn0.10Al0.10 (x = 0.08, 0.12, 0.20, 0.24, 0.28) hydrogen storage alloys

Phase structure and electrochemical properties of the Ml_1−xMg_xNi_2.80Co_0.50Mn_0.10Al_0.10 (x = 0.08, 0.12, 0.20, 0.24, 0.28) (Ml = La-rich mixed lanthanide) alloys were studied. X-ray diffraction (XRD) analysis and Rietveld refinement show that the alloys consist mainly of LaNi₅ and (La,Mg)Ni₃ phase. Due to variation in phases of the alloys, the maximum discharge capacity, the high rate dischargeability (HRD), and the low temperature dischargeability increase first and then decrease. The maximum discharge capacity increases from 322 mAh g⁻¹ (x = 0.08) to 375 mAh g⁻¹ (x = 0.12), and then decreases to 351 mAh g⁻¹ (x = 0.28) with increasing x. As the case of x = 0.20, HRD at 1200 mA g⁻¹ and discharge capacity at 233 K reaches 41.7% and 256 mAh g⁻¹, respectively. The cycling stability is improved by substituting La with Ml and B-site multi-alloying, and the capacity retention of Ml_0.72Mg_0.28Ni_2.80Co_0.50Mn_0.10Al_0.10 at the 200th cycle is 71%.     

Synthesis and electrochemical properties of Co-doped Li3V2(PO4)3 cathode materials for lithium-ion batteries

Co-doped Li₃V_2−xCo_x(PO₄)₃/C (x = 0.00, 0.03, 0.05, 0.10, 0.13 or 0.15) compounds were prepared via a solid-state reaction. The Rietveld refinement results indicated that single-phase Li₃V_2−xCo_x(PO₄)₃/C (0 ≤ x ≤ 0.15) with a monoclinic structure was obtained. The X-ray photoelectron spectroscopy (XPS) analysis revealed that the cobalt is present in the +2 oxidation state in Li₃V_2−xCo_x(PO₄)₃. XPS studies also revealed that V⁴⁺ and V³⁺ ions were present in the Co²⁺-doped system. The initial specific capacity decreased as the Co-doping content increased, increasing monotonically with Co content for x > 0.10. Differential capacity curves of Li₃V_2−xCo_x(PO₄)₃/C compounds showed that the voltage peaks associated with the extraction of three Li⁺ ions shifted to higher voltages with an increase in Co content, and when the Co²⁺-doping content reached 0.15, the peak positions returned to those of the unsubstituted Li₃V₂(PO₄)₃ phase. For the Li₃V_1.85Co_0.15(PO₄)₃/C compound, the initial capacity was 163.3 mAh/g (109.4% of the initial capacity of the undoped Li₃V₂(PO₄)₃) and 73.4% capacity retention was observed after 50 cycles at a 0.1 C charge/discharge rate. The doping of Co²⁺into V sites should be favorable for the structural stability of Li₃V_2−xCo_x(PO₄)₃/C compounds and so moderate the volume changes (expansion/contraction) seen during the reversible Li⁺ extraction/insertion, thus resulting in the improvement of cell cycling ability.     

Synthesis and electrochemical properties of submicron LiNi0.8Co0.2O2 by a polymer-pyrolysis method

A polymer-pyrolysis method was used to synthesize LiNi_0.8Co_0.2O₂, which has potential application in lithium ion batteries. The effect of calcination temperature and time on the structure and electrochemical performance of the material was investigated. XRD analysis showed that the powders obtained by calcination at 750 °C for 3 h had the best-ordered hexagonal layer structure. SEM image showed these powders were fine, narrowly distributed with platelet morphology. The charge-discharge tests demonstrated these powders had the best electrochemical properties, with an initial discharge capacity of 189 mAh/g and capacity retention of 95.2% after 50 cycles when cycled at 50 mA/g between 3.0 and 4.3 V. Besides, these powders also had exhibited excellent rate capability.     

Characterization of high tap density Li[Ni1/3Co1/3Mn1/3]O2 cathode material synthesized via hydroxide co-precipitation

Li[Ni_1/3Co_1/3Mn_1/3]O₂ cathode material for lithium ion batteries was prepared by mixing metal hydroxide, (Ni_1/3Co_1/3Mn_1/3)(OH)₂, with 6% excess LiOH followed by calcinations. The (Ni_1/3Co_1/3Mn_1/3)(OH)₂ with secondary particle of about 12 μm was prepared by hydroxide co-precipitation. The tap density of the obtained Li[Ni_1/3Co_1/3Mn_1/3]O₂ powder was 2.56 ± 0.21 g cm⁻³. The powder was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), particle size distribution (PSD) and galvanostatic charge-discharge cycling. The XRD pattern of Li[Ni_1/3Co_1/3Mn_1/3]O₂ revealed a well ordered hexagonal layered structure with low cation mixing. Secondary particles with size of 13-14 μm and primary particles with size of about 1 μm can be identified from the SEM observations. In the voltage range of 2.8-4.3 V, the initial discharge capacity of the Li[Ni_1/3Co_1/3Mn_1/3]O₂ electrode was 166.6 mAh g⁻¹, and 96.5% of the initial capacity was retained after 50 charge-discharge cycling.     

On the spinel formation in Co1 − xO/Co2TiO4 composites via reactive sintering, exsolution and oxidation

The formation mechanism and microstructural development of the spinel phases in the Co_1 − xO/Co₂TiO₄ composites upon reactive sintering the Co_1 − xO and TiO₂ powders (9:1 molar ratio) at 1450 °C and during subsequent cooling in air were studied by X-ray diffraction and analytical electron microscopy. The Co₂TiO₄ spinel occurred as inter- and intragranular particles in the matrix of Ti-doped Co_1 − xO grains with a rock salt-type structure during reactive sintering. The submicron sized Co₂TiO₄ particles were able to detach from grain boundaries in order to reach an energetically favorable parallel orientation with respect to the host Co_1 − xO grains via a Brownian-type rotation/coalescence process. Upon cooling in air, secondary Co₂TiO₄ nanoparticles were precipitated and the Ti-doped Co_1 − xO host was partially oxidized as Co_3 − δO₄ spinel by rapid diffusion along the {1 1 1} and {1 0 0}-decorated interphase interface and the free surface of the composites.     

Developing the properties of new blue phosphors: TiO2-doped Zn2SiO4

2ZnO + SiO₂ + X mol% TiO₂ (Zn₂SiO₄-X-TiO₂, 1 ≤ X ≤ 3) and 2ZnO + SiO₂ + 3 mol% MnO₂ (Zn₂SiO₄-3-TiO₂) compositions were prepared using nanoscale ZnO, SiO₂, TiO₂, and MnO₂ particles. The mixing powders were calcined between 1000 °C and 1300 °C in a N₂ atmosphere. Zn₂SiO₄ was the only phase in the calcined Zn₂SiO₄-X-TiO₂ phosphors. We found that the photoluminescence (PL) properties of synthesized Zn₂SiO₄-X-TiO₂ phosphors revealed these to be blue rather than green. The effects of TiO₂ content and calcining temperature on the PL properties of Zn₂SiO₄-X-TiO₂ phosphors were rigorously investigated.     

Structural investigation of Li1−xNi0.5Co0.25Mn0.25O2 by in situ XAS and XRD measurements

A combination technique of in situ synchrotron X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) was employed to study the Li_1−xNi_0.5Co_0.25Mn_0.25O₂ cathode material for Li-ion battery. The Li/Li_1−xNi_0.5Co_0.25Mn_0.25O₂ cell with x = 0.82 charged to 4.5 V showed the first charge capacity of 225 mAh/g. The X-ray absorption near edge structure (XANES) indicated that the initial valences were +2/+3, +3 and +4 for Ni, Co and Mn, respectively. The main redox reaction during delithiation was achieved by Ni via the reaction Ni²⁺ → Ni³⁺ followed by Ni³⁺ → Ni⁴⁺. The oxidation states of Co and Mn remained Co³⁺ and Mn⁴⁺. The bond length of Ni-O decreased drastically, while the Co-O and Mn-O distances exhibited a slight change with the decrease of Li content in the electrode. It was further revealed that all the second shell metal-metal (Ni-M, Co-M and Mn-O) distances decreased due to the oxidation of metal ions. In situ XRD data showed that both a- and c-axes varied with different Li contents in this material system. At the beginning of charge, there was a contraction along the c-axis and a slight expansion along the a-axis. As x reached 0.57, the trend of the variation in c-axis was opposite. The changes of lattice parameters could be explained by the balance between ionic radius and the repulsive force of the layer-structured material.     

Comparison of structure and electrochemistry of Al- and Fe-doped LiNi1/3Co1/3Mn1/3O2

LiNi_1/3Co_1/3−xM_xMn_1/3O₂ (M = Fe and Al; x = 0, 1/20, 1/9 and 1/6) have been synthesized by firing the co-precipitates of metal hydroxides. The impacts of Fe and Al doping on the structure and electrochemical performances of LiNi_1/3Co_1/3Mn_1/3O₂ are compared by means of powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and galvanostatic charge/discharge test as cathode materials for lithium ion batteries. These materials keep the same layered structure as the LiNi_1/3Co_1/3Mn_1/3O₂ host. It is found that Fe- and Al-doped LiNi_1/3Co_1/3Mn_1/3O₂ show different characteristics in lattice parameter and cycling voltage plateau with increasing dopant dose. More interestingly, low Al doping (x < 1/20) improves the structural stability while Fe doping does not have such effect even at low Fe content.     

Effect of fluorine in the preparation of Li(Ni1/3Co1/3Mn1/3)O2 via hydroxide co-precipitation

Uniform and spherical Li(Ni_1/3Co_1/3Mn_1/3)O_(2−δ)F_δ powders were synthesized via NH₃ and F⁻ coordination hydroxide co-precipitation. The effect of F⁻ coordination agent on the morphology, structure and electrochemical properties of the Li(Ni_1/3Co_1/3Mn_1/3)O_(2−δ)F_δ were studied. The morphology, size, and distribution of (Ni_1/3Co_1/3Mn_1/3)(OH)_(2−δ)F_δ particle diameter were improved in a shorter reaction time through the addition of F⁻. The study suggested that the added F improves the layered characteristics of the lattice and the cyclic performance of Li(Ni_1/3Co_1/3Mn_1/3)O₂ in the voltage range of 2.8-4.6 V. The initial capacity of the Li(Ni_1/3Co_1/3Mn_1/3)O_1.96F_0.04 was 178 mAh g⁻¹, the maximum capacity was 186 mAh g⁻¹ and the capacity after 50 cycles was 179 mAh g⁻¹ in the voltage range of 2.8-4.6 V.     

LiNi0.8Co0.15Al0.05O2 cathode materials prepared by TiO2 nanoparticle coatings on Ni0.8Co0.15Al0.05(OH)2 precursors

Synthesis, electrochemical, and structural properties of LiNi_0.8Co_0.15Al_0.05O₂ cathodes prepared by TiO₂ nanoparticles coating on a Ni_0.8Co_0.15Al_0.05(OH)₂ precursor have been investigated by the variation of coating concentration and annealing temperature. TiO₂-coated cathodes showed that Ti elements were distributed throughout the particles. Among the coated cathodes, the 0.6 wt% TiO₂-coated cathode prepared by annealing at 750 °C for 20 h exhibited the highest reversible capacity of 176 mAh g⁻¹ and capacity retention of 92% after 40 cycles at a rate of 1C (=190 mA g⁻¹). On the other hand, an uncoated cathode showed a reversible first discharge capacity of 186 mAh g⁻¹ and the same capacity retention value to the TiO₂-coated sample at a 1C rate. However, under a 1C rate cycling at 60 °C for 30 cycles, the uncoated sample showed a reversible capacity of 40 mAh g⁻¹, while a TiO₂-coated one showed 71 mAh g⁻¹. This significant improvement of the coated sample was due to the formation of a possible solid solution between TiO₂ and LiNi_0.8Co_0.15Al_0.05O₂. This effect was more evident upon annealing the charged sample while increasing the annealing temperature, and at 400 °C, the coated one showed a more suppressed formation of the NiO phase from the spinel LiNi₂O₄ phase than the uncoated sample.     

Hydrothermal synthesis of Li(Ni1/3Co1/3Mn1/3)O2 for lithium rechargeable batteries

Ultrafine powders of Li(Ni_1/3Co_1/3Mn_1/3)O₂ cathode materials for lithium-ion secondary batteries were prepared under mild hydrothermal conditions. The influence of the molar ratio of Li/(Ni + Co + Mn) was studied. The products were investigated by XRD, TEM and EDS. The final products were found to be well crystallized Li(Ni_1/3Co_1/3Mn_1/3)O₂ with an average particle size of about 10 nm.     

Effect of the starting materials on the reaction synthesis of Ti3SiC2

Ternary carbide of titanium and silicon was produced via mechanical milling and following heat treatment. Effects of the starting materials, milling time and heat treatment temperature were studied. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were utilized to evaluate the structural and morphological evolutions of the ball-milled and annealed powders. Results showed that the ball milling of TiO–Si–C as the starting materials failed to synthesize Ti₃SiC₂. Additionally, ball milling the elemental powders for shorter milling times resulted in the activation of the powders. However, after longer milling times, Ti–TiC nanocomposite was obtained. Furthermore, during annealing the milled powders, Ti₃SiC₂–TiC nanocomposite with the mean grain size of 16 nm was synthesized. After 20 h of milling, a very fine microstructure with narrow size of distribution and spheroid particles was achieved.