One-step solid-state synthesis of nanosized LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> cathode material with power properties

A simple one-step solid state reaction way of preparing nanosized LiMn₂O₄ powders with high-rate properties is investigated. Oxalic acid is used as a functional material to lose volatile gases during the process of calcining in order to control the morphology and change the particle size of materials. The results of X-ray diffraction and scanning electron microscopy show that particle size of materials decreases with the increase of the oxalic acid content. The electrochemical test results indicate that optimal LiMn₂O₄ particles (S_0.5) is synthesized when the molar ratios of oxalic acid and total Mn source are 0.5:1. It also manifests that LiMn₂O₄ sample with middle size has the optimal electrochemical performance among five samples instead of the smallest LiMn₂O₄ sample. The obtained sample S_0.5 with middle size exhibits a high initial discharge capacity of 125.8 mAh g^?1 at 0.2C and 91.4% capacity retention over 100 cycles at 0.5C, superior to any one of other samples. In addition, when cycling at the high rate of 10C, the optimal S_0.5 in this work could still reach a discharge capacity of 80.8 mAh g^?1. This observation can be addressed to the fact that the middle size particles balance the contradictory of diffusion length in solid phase and particle agglomeration, which leads to perfect contacts with the conductive additive, considerable apparent Li-ion diffusion rate, and the optimal performance of S_0.5.     

Synthesis of LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> nano/microspheres with adjustable hollow structures for lithium-ion battery

High-voltage spinel LiNi_0.5Mn_1.5O₄ nano/microspheres with adjustable hollow structures have been fabricated based on the Kirkendall effect. The main characteristic is that the wall thickness of the hollow structure as well as the cavity size of the hollow structure can be adjusted by the different ratio of mixed precipitation agents. Especially, the diagrammatic sketch for the formation process of various LiNi_0.5Mn_1.5O₄ materials with adjustable hollow structures is discussed. Besides, the results of electrochemical performance test show that LiNi_0.5Mn_1.5O₄ obtained from 10:1 Na₂CO₃/NaOH (in mole) ratio is worth looking forward to, owing to its special hierarchical nano/microsphere and moderate hollow structures.     

An insight into the influence of crystallite size on the performances of microsized spherical Li(Ni<Subscript>0.5</Subscript>Co<Subscript>0.2</Subscript>Mn<Subscript>0.3</Subscript>)O<Subscript>2</Subscript> cathode material composed of aggregated nanosized particles

Relationships between the performance and the crystallite size of the microsized spherical Li(Ni_0.5Co_0.2Mn_0.3)O₂ cathode material composed of aggregated nanosized primary particles have been comprehensively studied. The cathode material was synthesized by a high-temperature solid-state method. The results obtained by XRD, Rietveld refinement, SEM, HR-TEM, DSC, and galvanostatic test show that the crystallite size (XS) of Li(Ni_0.5Co_0.2Mn_0.3)O₂ is greatly affected by the temperature in the range of 750 to 820 °C. Most of all, the crystallite size plays a unique role in the performance of the material. That is, the electrochemical characteristics of Li(Ni_0.5Co_0.2Mn_0.3)O₂, such as discharge capacity, rate performance, and thermal stability, are closely related to the crystallite size. Furthermore, the retention of discharge capacity is determined by that of crystallite size in Li(Ni_0.5Co_0.2Mn_0.3)O₂ after 100 cycles.     

Effects of lithium excess amount on the microstructure and electrochemical properties of LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> cathode material

Spinel LiNi_0.5Mn_1.5O₄ cathode materials with different lithium excess amount (0, 2%, 6%, 10%) were synthesized by a facile solid-state method. The effect of lithium excess amount on the microstructure, morphology, and electrochemical properties of LiNi_0.5Mn_1.5O₄ materials was systematically investigated. The results show that the lithium excess amount does not change the particle morphology and size obviously; thus, the electrochemical properties of LiNi_0.5Mn_1.5O₄ are mainly determined by structural characteristics. With the increase of lithium excess amount, the cation disordering degree (Mn³⁺ content) and phase purity first increase and then decrease, while the cation mixing extent has the opposite trend. Among them, the LiNi_0.5Mn_1.5O₄ material with 6% lithium excess amount exhibits higher disordering degree and lower impurity content and cation mixing extent, thus leading to the optimum electrochemical properties, with discharge capacities of 125.0, 126.1, 124.2, and 118.9 mAh/g at 0.2-, 1-, 5-, and 10-C rates and capacity retention rate of 96.49% after 100 cycles at 1-C rate.     

Influence of sintering temperature and pH on the phase transformation,particle size and anti-reflective properties of RHA nano silica powders

Nano silica powders were synthesized from rice husk ash, the most silica-rich raw material, using alkaline extraction followed by acid precipitation. The phase transformation during sintering, the influence of sintering temperature and pH on the particle size and anti-reflective properties of nano silica were investigated. The results showed that the amorphous SiO₂ sintered at 600°C were transformed to a cristobalite structures completely during the sintering process at 800°C and 1100°C. With the increasing sintering temperature and pH, the particle size distributions (d₅₀) were increased respectively in the range of 62–84, 192–240, and 283–329?nm at sintering temperatures of 600°C, 800°C, and 1100°C. When the sintering temperatures were increased at 1100°C, 98.15% and 96.84% of transmittances were obtained respectively at the highest and lowest points of the anti-reflection band and could be used for anti-reflective applications.     

Preparation and characterization of LiTi<Subscript>2</Subscript>O<Subscript>4</Subscript> anode material synthesized by one-step solid-state reaction

LiTi₂O₄ anode material for lithium-ion battery has been prepared by a novel one-step solid-state reaction method using Li₂CO₃, TiO₂, and carbon black as raw materials. X-ray diffraction, scanning electron microscopy, energy-dispersive spectrometry, and the determination of electrochemical properties show that the single phase of LiTi₂O₄ with spinel crystal structure is formed at 850?°C by this new method, and the lattice parameter is about 8.392?Å. The primary particle size of the LiTi₂O₄ powder is about 0.5–1.0 μm and its morphology is similar to a sphere. The lithium ion insertion voltage of LiTi₂O₄ anode material is about 1.50 V versus lithium metal, the initial discharge capacity is about 133.6 mAh g^-1, the charge–discharge voltage plateau is very flat, and no solid electrolyte interface film is formed when working potential is more than 1.0 V. The reaction reversibility and the cycling stability are excellent, and the high rate performance is good.     

LiFePO<Subscript>4</Subscript>/C with high capacity synthesized by carbothermal reduction method

The olivine-type LiFePO₄/C cathode materials were prepared via carbothermal reduction method using cheap Fe₂O₃ as raw material and different contents of glucose as the reducing agent and carbon source. Their structural and morphological properties were investigated by X-ray diffraction, scanning electron microscope, transmission electron microscope, and particle size distribution analysis. The results demonstrated that when the content of the carbon precursor of glucose was 16 wt.%, the synthesized powder had good crystalline and exhibited homogeneous and narrow particle size distribution. Even and thin coating carbon film was formed on the surface of LiFePO₄ particles during the pyrolysis of glucose, resulting in the enhancement of the electronic conductivity. Electrochemical tests showed that the discharge capacity first increased and then decreased with the increase of glucose content. The optimal sample synthesized using 16 wt.% glucose as carbon source exhibited the highest discharge capacity of 142 mAh g⁻¹ at 0.1C rate with the capacity retention rate of 90.4% and 118 mAh g⁻¹ at 0.5C rate.     

Structural and magnetic properties of size-controlled Mn<Subscript>0.5</Subscript>Zn<Subscript>0.5</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles and magnetic fluids

Mn_0.5Zn_0.5Fe₂O₄ ferrite nanoparticles with tunable Curie temperature and saturation magnetization are synthesized using hydrothermal co-precipitation method. Particle size is controlled in the range of 54 to 135 Å by pH and incubation time of the reaction. All the particles exhibit super-paramagnetic behaviour at room temperature. Langevin’s theory incorporating the interparticle interaction was used to fit the virgin curve of particle magnetization. The low-temperature magnetization follows Bloch spin wave theory. Curie temperature derived from magnetic thermogravimetric analysis shows that Curie temperature increases with increasing particle size. Using these particles magnetic fluid is synthesized and magnetic characterization is reported. The monolayer coating of surfactant on particle surface is confirmed using thermogravimetric measurement. The same technique can be extended to study the magnetic phase transition. The Curie temperature derived using this measurement complies with the low-temperature magnetic measurement. The room-temperature and high-temperature magnetization measurements are also studied for magnetic fluid systems. The magnetic parameters derived for fluid are in good agreement with those obtained for the particle system.     

Synthesis,structural and electrical properties of double perovskite Sr<Subscript>2</Subscript>NiMoO<Subscript>6</Subscript> ceramics

The double perovskite Sr₂NiMoO₆ powders and ceramics were prepared by two different (conventional and precursor) solid-state reaction methods. The phase structure was characterized by XRD and TEM techniques. It has been indicated that single-phase perovskite powders were obtained when calcined in air at 1300°C. However, nano-particles of the size 30–60 nm have been found in powders prepared with the precursor method, while those from the conventional route exhibit large irregular shaped particles with aggregation. The dielectric properties (ε _r and tanδ) were also examined in the sintered ceramics. The results showed the transition point at 280°C for conventional route, while no clear phase change was observed in ceramics from the precursor route. These observations clearly indicate that the different starting processes affected the phase formation behavior and the electrical properties of Sr₂NiMoO₆ ceramics.     

Morphology modification of TiO<Subscript>2</Subscript> nanotubes by controlling the starting material crystallite size for chemical synthesis

TiO₂ nanotubes (NTs) were prepared by low-temperature chemical synthesis using anatase TiO₂ particles with different crystallite sizes in a NaOH solution followed by water washing and HCl neutralization. The synthesized TiO₂ NTs showed diverse morphologies depending on the starting materials. The crystallite size of TiO₂ raw materials increased with an increase in annealing temperature, and larger TiO₂ NTs, around 31 nm in diameter, were obtained from large raw powder with a crystallite size of 117 nm. X-ray diffraction and Raman spectroscopy revealed that the obtained TiO₂ NT exhibited lower crystallinity; however, Raman vibration seems to be more likely than a rutile structure.     

Preparation of LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> cathode materials by electrospinning

LiNi_0.5Mn_1.5O₄ cathode material was prepared by electrospinning using lithium hydroxide, manganese acetate, nickel acetate, acetic acid, ethanol, and poly(vinyl pyrrolidone) as raw materials. The effect of calcination temperature on the structure, morphology, and electrochemical properties was investigated. XRD results indicate that the LiNi_0.5Mn_1.5O₄ composite is well crystallized as a spinel structure at calcination temperature of 650 °C for 3 h. SEM results reveal that this composite has a nanofiber shape with average size of about 300–500 nm. Electrochemical performance tests reveal that this composite shows the initial discharge capacity of 127.8 and 105 mAhg^?1 at 0.1 and 3 C rates, respectively, and exhibits good cycling performance.     

Effect of PVA addition on formation of spray-deposited Sm<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>CoO<Subscript>3</Subscript> thin films on CeO<Subscript>2</Subscript> substrates

Nano-crystalline films of Sm_0.5Sr_0.5CoO₃ (SSC) have been formed on CeO₂ substrates by spraying stoichiometric aqueous solution containing Sm, Sr, and Co ions. Effect of polyvinyl alcohol (PVA) addition as a complexing agent in spray solution on stoichiometry, crystallite size, morphology, and transport properties of film are studied. The results showed that the SSC cathode had maximum crystallite size for 40% PVA addition. Electrical performance of film decreases with decrease in the particle size, while the electronic to ionic predominance transition temperature decreases with decreasing particle size. These films are studied for their potential application as a cathodic material in developing intermediate temperature solid oxide fuel cells.     

Synthesis of spinel LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.5</Subscript>O<Subscript>4</Subscript> as advanced cathode via a modified oxalate co-precipitation method

Spinel-type LiNi_0.5Mn_1.5O₄ (LNMO) cathode materials for lithium ion batteries have been synthesized via a modified oxalate co-precipitation method. By virtue of the co-precipitation of Li⁺ with transition metal ions, the target materials can be obtained through one-pot reaction without subsequent mixing with lithium salts. What’s more, a uniform distribution between the lithium and transition metal ions at molecular level could be realized, which is beneficial for final electrochemical performances. The physical and electrochemical properties of the material are characterized by XRD, TGA, EDS, FT-IR, SEM, CV, EIS, and charge/discharge tests. The results prove that the as-prepared material owns a cubic spinel structure with a space group of Fd-3m, high crystallinity, uniform particle size, and excellent electrochemical performances. A higher initial capacity and superior rate performance are delivered compared with that of material by conventional co-precipitation method. High capacities of 131.7 and 104.0 mAh g^?1 could be displayed at 0.5 and 10 C, respectively. Excellent cycle stability is also demonstrated with more than 98.5 % capacity retention after 100 cycles at 1 C.     

Preparation and characterization of Yb-doped Ba(Ce,Zr)O<Subscript>3</Subscript> nanopowders with high sinterability

The Ba(Ce_0.8Zr_0.2)_0.95Yb_0.05O_2.975 ceramics electrolyte was prepared via a Pechini method using metal nitrate salts as starting materials. An optimum annealing temperature of 1,400 °C was needed to obtain a pure perovskite-like phase with orthorhombic structure. Particle size distribution showed a bimodal distribution that corresponds to the loose powders and agglomerates size. Scanning electron micrograph revealed that the loose powders were in the nanosize range (70–200 nm). These ultrafine loose powders enhanced the densification of a pellet with relative density ∼95% obtained at 1,400 °C. The sample formed clear and compact grains with submicron sizes. Impedance results showed that the impedance semicircle of the grain was observed only at T ≤ 250 °C. The introduction of 20 mol% Zr improved the chemical stability of BaCe_0.95Yb_0.05O_2.975 sample in atmosphere containing carbon dioxide at 600 °C. The sample also exhibited high proton conductivity in wet hydrogen.     

Structural evolutions of the mechanically alloyed Al<Subscript>70</Subscript>Cu<Subscript>20</Subscript>Fe<Subscript>10</Subscript> powders

Elemental mixtures of Al, Cu, Fe powders with the nominal composition of Al₇₀Cu₂₀Fe₁₀ were mechanically alloyed in a planetary ball mill for 80 h. Subsequent annealing of the as-milled powders were performed at 600–800°C temperature range for 4 h. Structural characteristics of the mechanically alloyed Al₇₀Cu₂₀Fe₁₀ powders with the milling time and the heat treatment were investigated by X-ray diffraction (XRD), differential scanning calorimeter (DSC) and differential thermal analysis (DTA). Mechanical alloying of the Al₇₀Cu₂₀Fe₁₀ did not result in the formation of icosahedral quasicrystalline phase (i-phase) and a long time milling resulted in the formation of β-Al(Cu,Fe) solid solution phase (β-phase). The i-phase was observed only for short-time milled powders after heat treatment above 600°C. The β-phase was one of the major phases in the Al₇₀Cu₂₀Fe₁₀ alloy. The w-Al₇Cu₂Fe₁ phase (w-phase) was obtained only after heat treatment of the short-time milled and unmilled samples. The present investigation indicated that a suitable technique to obtain a large amount of quasicrystalline powders is to use a combination of short-time milling and subsequent annealing.     

A study of the structure and properties of nanostructured ZrO<Subscript>2</Subscript>-Y<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composite powders

The correlation between temperature treatment conditions and the ratio of components in nanostructured fibrous powders with a composition of ZrO₂-Y₂O₃-Al₂O₃ and their porous crystal structure and physicochemical properties is studied. The dependences of the ratio between zirconia tetragonal and monoclynic phases on the treatment temperature and the alumina content are found to have a nonmonotonic character. The growth of zirconia crystallite size is suppressed by introduced nanocrystalline alumina in a temperature range of 600–1200°C, which is caused by the processes of ternary solid solution formation. The bulk and picnometric density values of materials are proportional to the temperature of heat treatment. The temperature dependence of the specific surface and the size of oxide grain particles has an inversely proportional character. With increasing alumina content in the powders, the specific surface increases, while the picnometric and bulk densities decrease.     

Preparation and properties of Zn<Subscript>0.9</Subscript>Ni<Subscript>0.1</Subscript>O diluted magnetic semiconductor nanoparticles

With a view to study the structural, electronic, magnetic, and electrical properties of Zn_0.9Ni_0.1O diluted magnetic semiconductor nanoparticles, systematic investigation has been undertaken. Samples were prepared for the first time by hydrazine-assisted polyol method, and the powders were annealed at various temperatures in order to obtain the samples with different grain sizes. From the Rietveld refined XRD data, lattice parameters, the average crystallite size values, and r.m.s micro-strain values were computed. From the AFM and TEM studies, the average particle sizes were obtained and are found to be in the range 12–46 nm. XPS measurements clearly indicate that the chemical states as +2 for both Zn and Ni ions and are stable with varying annealing temperature. Further, using XPS and optical studies, the electronic structure of the materials was analyzed. A careful phase analysis of the Rietveld refined XRD data (at logarithmic scale) selected area electron diffraction patterns, FTIR, Raman, and XPS studies; it was concluded that all the samples are having hexagonal wurtzite structure without any detectable impurity phases. The optical band gap values are found to exhibit a clear blue shift. The influence of oxygen vacancies on the emission spectra was studied by Photo Luminescence measurement. The magnetization studies were undertaken by VSM, MFM, and FMR techniques and confirmed the presence of clear room temperature ferromagnetism without any magnetic clusters. The carrier concentration (n) values obtained from the thermo power studies are found to decrease with increasing annealing temperature and depend on the local defects which are critically influenced by the annealing temperature and crystallite size of the nanomaterials.     

Fabrication and laser performance of highly transparent Nd:YAG ceramics from well-dispersed Nd:Y<Subscript>2</Subscript>O<Subscript>3</Subscript> nanopowders by freeze-drying

Well-dispersed Nd:Y₂O₃ powders with uniform particle size of about 60 nm were synthesized from freeze-dried precursors. Highly transparent 2 at.% Nd:YAG ceramics were fabricated from the as-synthesized Nd:Y₂O₃ powders and commercial Al₂O₃ powders by vacuum sintering at 1,750 °C for 5 h. Phase evolution, microstructures, and spectroscopic properties of the Nd:YAG transparent ceramics were investigated. Freeze-drying played an important role in the synthesis of high-quality Nd:Y₂O₃ nanosized powders, which were essential for the fabrication of highly transparent Nd:YAG ceramics. Optical transmittance of a 3-mm thick sample reached 82% in the wavelength range of 200–900 nm. 5.23 W output power was obtained with 14.3 W diode laser pumping, giving a slope efficiency of 36.5%.     

Diversity of TiO<Subscript>2</Subscript> nanopowders’ characteristics relevant to toxicity testing

In this study, the physicochemical properties of several commercial ultrafine TiO₂ powders and their behaviour in the as-received form and colloidal suspensions were analysed. Besides the particle size, the morphology and agglomeration state of the dry powders, dispersibility, ζ-potential and sedimentation in water and in phosphate-buffered saline (PBS) were studied. Also, leaching of ions from the powders during ageing in physiological solution and the ability of the photoactivated powders to decompose organic substances were evaluated. The examined TiO₂ powders revealed diversified characteristics when dispersed in water. In general, while in dry conditions the particle size appeared in the nano-range (down to 32 nm), the particles were agglomerated in aqueous suspensions at pH ~7 and only a minor amount showed dimensions below 200 nm, but none below 100 nm. The inherent pH of the 3 % suspensions varies from 3.7 to 7.5 and the surface charge at these pH values varied from highly positive to highly negative values. In PBS, the surface charge is negative and relatively low for all the samples, which resulted in agglomeration. Five out of six powders exhibited significant photocatalytic activity when exposed to UV irradiation. This also includes one cosmetic-grade powder. Furthermore, during the immersion in aqueous media at physiological temperature, the powders released foreign ions, which might also contribute to the results of cytotoxicity tests. The results revealed the major role of the particle surface charge and its impact on particle dispersion or agglomeration. Due to the high ionic strength in the liquids relevant for cell-surface interaction tests, for all the examined titania powders the nanoparticulate character was lost. However, the presence of impurities and photocatalysis might further contribute to the results of cytotoxicity tests.     

ZnO-coated LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> cathode material for lithium-ion batteries synthesized by a combustion method

ZnO-coated LiMn₂O₄ cathode materials were prepared by a combustion method using glucose as fuel. The phase structures, size of particles, morphology, and electrochemical performance of pristine and ZnO-coated LiMn₂O₄ powders are studied in detail by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), galvanostatic charge-discharge test, and X-ray photoelectron spectroscopy (XPS). XRD patterns indicated that surface-modified ZnO have no obvious effect on the bulk structure of the LiMn₂O₄. TEM and XPS proved ZnO formation on the surface of the LiMn₂O₄ particles. Galvanostatic charge/discharge test and rate performance showed that the ZnO coating could improve the capacity and cycling performance of LiMn₂O₄. The 2 wt% ZnO-coated LiMn₂O₄ sample exhibited an initial discharge capacity of 112.8 mAh g^?1 with a capacity retention of 84.1 % after 500 cycles at 0.5 C. Besides, a good rate capability at different current densities from 0.5 to 5.0 C can be acquired. CV and EIS measurements showed that the ZnO coating effectively reduced the impacts of polarization and charge transfer resistance upon cycling.