Sodium gluconate-assisted hydrothermal synthesis,characterization and electrochemical performance of LiFePO4 powders

Nano- and micro-sized LiFePO₄ powders were synthesized by a sodium gluconate (C₆H₁₁NaO₇)-assisted hydrothermal synthesis method at 220 °C for 10 h with pH = 2–7. The resulting powders were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and energy-dispersive X-ray spectrometer (EDS). The obtained data showed that the pH of synthesis solution played a key role in the formation of the LiFePO₄ powders with different morphologies, such as ball-like microspheres, irregular microspheres with the agglomerated rods and particles, sphere-like nanoparticles and nano-ellipsoids. The results from electrochemical performance measurements revealed that the charge–discharge cycling characteristics of the samples were strongly dependent on their morphologies. In particular, the ellipsoidal LiFePO₄ nanoparticles with the average size of 70–90 nm showed the highest initial discharge capacity of 150 mA h g⁻¹ at 0.1 C rate, and cycling stability of the ellipsoidal LiFePO₄ nanoparticles was optimum among all the samples prepared due to their dual advantages of high tap density and good diffusion property. The present study offers a simple morphology-controllable route, without carbon coating or doping with supervalent cations, to synthesize and to design high performance cathode materials for lithium-ion batteries.     

Synthesis,characterization, and thermodynamic parameters of vanadium dioxide

A novel process was developed for synthesizing pure thermochromic vanadium dioxide (VO₂) by thermal reduction of vanadium pentoxide (V₂O₅) in ammonia gas. The process of thermal reduction of V₂O₅ was optimized by both experiments and modeling of thermodynamic parameters. The product VO₂ was characterized by means of X-ray diffraction (XRD), X-ray photoelectron spectrometry (XPS), scanning electron microscopy (SEM), thermogravimetric analysis (TG), and differential scanning calorimetry (DSC). The experimental results indicated that pure thermochromic VO₂ crystal particles were successfully synthesized. The phase transition temperature of the VO₂ is approximately 342.6 K and the enthalpy of phase transition is 44.90 J/g.     

Effect of carbon content and calcination temperature on the electrochemical performance of lithium iron phosphate/carbon composites as cathode materials for lithium-ion batteries

Lithium iron phosphate/carbon (LiFePO₄/C) composites were prepared by a convenient method with water-soluble phenol-formaldehyde resin as the carbon precursor. The morphology, crystalline structure, thermal stability, and composition of as-prepared LiFePO₄/C composites were investigated by scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, and Raman spectrometry. Their electrochemical performance was examined based on cyclic voltammogram with a LAND battery testing system while the effect of carbon content and calcination temperature was highlighted. Results show that carbon content and calcination temperature dramatically influence the discharge capacities and rate performance of LiFePO₄/C composites. The optimal calcination temperature is 700 °C, and the optimal carbon content (mass fraction) is 8.7%. The LiFePO₄/C composite prepared under the optimal conditions exhibits an initial room temperature discharge capacity of 150.2 mA h g^?1 at a 0.2 C rate and a constant discharge capacity of about 105.7 mA h g^?1 at a 20.0 C rate after 50 cycles, showing promising potential as a novel cathode material for lithium ion batteries.     

Nb2O5 hollow nanospheres as anode material for enhanced performance in lithium ion batteries

Nb₂O₅ hollow nanospheres of average diameter ca. ～29 nm and hollow cavity size ca. 17 nm were synthesized using polymeric micelles with core–shell–corona architecture under mild conditions. The hollow particles were thoroughly characterized by transmission electron microscope (TEM), X-ray diffraction (XRD), infrared spectroscopy (FTIR), thermal (TG/DTA) and nitrogen adsorption analyses. Thus obtained Nb₂O₅ hollow nanospheres were investigated as anode materials for lithium ion rechargeable batteries for the first time. The nanostructured electrode delivers high capacity of 172 mAh g^?1 after 250 cycles of charge/discharge at a rate of 0.5 C. More importantly, the hollow particles based electrodes maintains the structural integrity and excellent cycling stability even after exposing to high current density 6.25 A g^?1. The enhanced electrochemical behavior is ascribed to hollow cavity coupled with nanosized Nb₂O₅ shell domain that facilitates fast lithium intercalation/deintercalation kinetics.     

Molten salt synthesis and electrochemical properties of spherical LiFePO4 particles

Well-crystallized LiFePO₄ was directly synthesized by the KCl molten salt (MS) method. According to this method, the pre-sintered intermediate was mixed with KCl, and then sintered at a certain temperature, which was determined by thermogravimetric analysis (TGA). The olivine structure and spherical morphology were confirmed by X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM). The spherical products show a higher tap density, which will benefit the enhancement of volumetric energy density. The electrochemical behavior was studied by cyclic voltammetry and galvanostatic tests. The LiFePO₄ product sintered at 755 °C for 3 h exhibits the best electrochemical performance. At a rate of 0.1 C, it can deliver an initial capacity of 130.3 mAh g^− 1, and a capacity of 137.2 mAh g^− 1 at the 40th cycle. At a high discharge rate of 5 C, it still exhibits a capacity of 92 mAh g^− 1.     

Phase and morphology evolution of bismuth ferrites via hydrothermal reaction route

Phase-controlled synthesis of bismuth ferrites has been achieved via hydrothermal route by adjusting the KOH concentration. The as-prepared powders were characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, and selected area electron diffraction. The particle morphologies of the as-prepared powders evolve from nanoflakes, to self-assembled particles, and microparticles when the concentration of KOH was changed from 1.5 M, 2.5 M, to 3.5 M, and 5 M. Correspondingly, the main phase of the samples changed from orthorhombic Bi₂Fe₄O₉, both Bi₂Fe₄O₉ and BiFeO₃, to pure rhombohedral BiFeO₃. On the basis of these experiments, the phase formation and morphology evolution mechanism of the samples are discussed. Furthermore, the photocatalytic activity of the as-prepared samples was investigated by the photo-degradation of rhodamine-B solution.     

Solvothermal synthesis of monodispersed CoZr4(PO4)6 microspheres and their application as microwave absorber

Monodispersed CoZr₄(PO₄)₆ microspheres with a diameter of 40 μm were achieved via a combining solvothermal and calcination route. The crystallinity of the calcined microspheres with shell structure was improved, while the monodisperse property and morphologies remained. The possible formation mechanism of the porous CoZr₄(PO₄)₆ microspheres with nanoshell was proposed. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectra (FT-IR) technologies, thermal analysis (TG and DSC), nitrogen adsorption–desorption isotherms and network analyzer. The sample calcined at 900 °C shows a strongest absorbability in the radar-wave absorbability test.     

Sol–gel synthesis and lithium ion conduction properties of garnet-type Li6BaLa2Ta2O12

High lithium ion conductive garnet-type barium lanthanum lithium tantalate, Li₆BaLa₂Ta₂O₁₂ (LLBTO), was prepared by a modified sol–gel Pechini method from the appropriate mixtures of lithium carbonate, lanthanum oxide, barium carbonate and tantalum ethoxide. The thermal decomposition of the precursor powder was investigated by TG/DTA analysis. The LLBTO precursor powders were annealed at various temperatures between 923 and 1123 K for 6 h in air. The transformation process from precursor powder to crystalline garnet-like phase was analyzed by X-ray powder diffraction (XRPD). The morphology of the powders annealed at various temperatures was investigated by scanning electron microscopy (SEM). The resultant pelletized Li₆BaLa₂Ta₂O₁₂, prepared by sol–gel synthesis method, shows a total Li-ion conductivity of 1.69 × 10^?5 S/cm at 298 K and an activation energy is 0.40 eV. The ionic conductivities reported in this study are slightly higher than those reported for LLBTO sample synthesized by conventional solid state synthesis route.     

High-rate performance of xLiFePO4·yLi3V2(PO4)3/C composite cathode materials synthesized via polyol process

xLiFePO₄·yLi₃V₂(PO₄)₃/C composite cathode materials were synthesized via a polyol process, using LiOH·H₂O, Fe₃(PO₄)₂·8H₂O, V₂O₅ and H₃PO₄ as raw materials, citric acid and PEG as carbon sources, and TEG as both a solvent and a reductant. Structural and morphological characterizations of as-prepared materials were carried out by X-ray diffraction (XRD) as well as scanning electron microscopy (SEM), respectively. Furthermore, electrochemical properties of as-prepared materials were analyzed by charge–discharge tests, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). XRD results indicated that the composites consisting of an olivine phase of LiFePO₄ and a monoclinic phase of Li₃V₂(PO₄)₃ are well-crystallized. It is found that the LF_0.6P·LV_0.4P/C composite exhibited better electrochemical performance than pristine LFP/C and LVP/C at 5 C and 10 C rate and delivered 126 mAh g^?1 and 110 mAh g^?1, respectively. The favorable particles morphology with less than 100 nm size and low extent agglomeration is believed as a factor. In addition, the co-existence of V³⁺-doped LiFePO₄/C and Fe²⁺-doped Li₃V₂(PO₄)₃/C was supposed as another reason.     

Microwave-induced combustion synthesis of Li0.5Fe2.5−xCrxO4 powder and their characterization

Li_0.5Fe_2.5−xCr_xO₄ (0 ≦ x ≦ 1.0) powders with small and uniformly sized particles were successfully synthesized by microwave-induced combustion, using lithium nitrate, iron nitrate, chromium nitrate, and carbohydrazide as the starting materials. The process takes only a few minutes to obtain as-received Cr-substituted lithium ferrite powders. The resultant powders annealed at 650 °C for 2 h and were investigated by thermogravimeter/differential thermal analyzer (TG/DTA), X-ray diffractometer (XRD), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), and thermomagnetic analysis (TMA). The results revealed that the lattice constant decreases linearly with increasing of Cr content in Li_0.5Fe_2.5−xCr_xO₄ specimens. Moreover, the magnetic properties of Cr-substituted lithium ferrite were also strongly affected by Cr content. The saturation magnetization, remanent magnetization, and coercive force decrease monotonously with increasing of Cr content.     

Synthesis and characterization of a new organic sulphate, [2,3-(CH3)2C6H3NH3]HSO4·H2O

Crystals of a new hybrid compound C₈H₁₂N⁺, HSO₄^?·H₂O were synthesized in aqueous solution and characterized by X-ray diffraction and IR absorption spectroscopy. This compound crystallizes in the orthorhombic non-centrosymmetrical space group P2₁2₁2₁ and an unit cell with a = 5.74(2) Å, b = 9.17(2) Å, c = 21.34(4) Å, V = 1124(6) Å³, and Z = 4. Its crystal structure is a packing of alternated inorganic and organic layers parallel to (a,b) planes. The different components are connected by a bi-dimensional network of strong OH…O and NH…O hydrogen bonds. Then, in order to detect phase transitions and watch changes in the conductivity behaviour, investigations by DTA–TG and differential scanning calorimetry (DSC) and electrical conductivity measurements were carried out.     

Structure,nonstoichiometry, sintering and oxygen permeability of perovskite SrCo1−2x(Fe,Nb)xO3−δ (x = 0.05, 0.10) oxides

The novel Fe/Nb co-substituted SrCo_1?2x(Fe,Nb)_xO_3?δ (x = 0.05, 0.10) oxides have been synthesized and characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetry (TG), and scanning electron microscopy (SEM). The XRD and DSC results demonstrate that the structural stability of the Fe/Nb co-substituted samples x = 0.05, 0.10 is improved greatly compared to the sample x = 0.00. The Fe/Nb co-doping in the SrCoO_3?δ oxide results in the improved structural stability of the SrCo_1?2x(Fe,Nb)_xO_3?δ (x = 0.05, 0.10) oxides. The nonstoichiometric and sintering properties were investigated by TG and SEM, and the oxygen permeation fluxes were measured at 800–950 °C for the sample x = 0.10. The improved oxygen permeability of the ceramic SrCo_1?2x(Fe,Nb)_xO_3?δ (x = 0.10) membrane compared to the (Ba_0.5Sr_0.5)(Co_0.8Fe_0.2)O_3?δ and SrCo_0.8Fe_0.2O_3–δ membranes, was observed under an air/He oxygen partial pressure gradient at 800–950 °C.     

A study on the phase transformation of the nanosized hydroxyapatite synthesized by hydrolysis using in situ high temperature X-ray diffraction

The biodegradable hydroxyapatite (HA) was synthesized by hydrolysis and characterized using high temperature X-ray diffraction (HT-XRD), differential thermal analysis and thermogravimetry (DTA/TG), and scanning electron microscopy (SEM). The in situ phase transformation of the HA synthesized from CaHPO₄·2H₂O (DCPD) and CaCO₃ with a Ca / P = 1.5 in 2.5 M NaOH_(aq) at 75 °C for 1 h was investigated by HT-XRD between 25 and 1500 °C. The HA was crystallized at 600 °C and maintained as the major phase until 1400 °C. The HA steadily transformed to the α-tricalcium phosphate (α-TCP) which became the major phosphate phase at 1500 °C. At 700 °C, the minor CaO phase appeared and vanished at 1300 °C. The Na⁺ impurity from the hydrolysis process was responsible for the formation of the NaCaPO₄ phase, which appeared above 800 °C and disappeared at 1200 °C.     

Thermal decomposition synthesis of 3D urchin-like α-Fe2O3 superstructures

Urchin-like α-Fe₂O₃ superstructures have been deposited on Si substrate using thermal decomposition FeCl₃ solution at 200–600 °C in the oven. The morphologies and structures of the synthesized urchin-like superstructures have been characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The results show that urchin-like α-Fe₂O₃ superstructures were a polycrystal with the rhombohedral structure and typical diameters of 16–20 nm and lengths up to 1.0 μm. The as-prepared α-Fe₂O₃ superstructures have a high Brunauer–Emmett–Teller (BET) surface area of about 60.24 m²/g. The photoluminescence spectrum of the urchin-like α-Fe₂O₃ superstructures consists of one weak emission peak at 548 nm (2.26 eV). A possible new mechanism for the formation of the urchin-like superstructures was also preliminarily discussed.     

Host-sensitized phosphorescence of Mn4+, Pr3+,4+ and Nd3+ in MgAl2Si2O8

Mn⁴⁺ doped and Pr^3+,4+, Nd³⁺ co-doped MgAl₂Si₂O₈-based phosphors were first of all synthesized about 1300 °C. They were characterized by thermogravimetry (TG), differential thermal analysis (DTA), X-ray powder diffraction (XRD), photoluminescence (PL) and scanning electron microscopy (SEM). The luminescence mechanism of the phosphors, which showed broad red emission bands in the range of 610–715 nm and had a different maximum intensity when activated by UV illumination, was discussed. Such a red emission can be attributed to the intrinsic d–d transitions of Mn⁴⁺.     

Synthesis and characterization of MFe2O4 (M = Mg,Mn, Ni) nanoparticles

MFe₂O₄ nanoparticles were obtained in the presence of natural compounds as carboxymethylcellulose (CMC). The CMC polymer had a double function as a capping agent and as a protecting agent in the growth process of nanoparticles. The synthesized nanoparticles were characterized using thermal analysis (TG, DTA, DTG), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and a vibrating sample magnetometer (VSM). The XRD patterns indicate that all the samples were formed in single phase spinel structure. The results also show that the samples calcinated at 500 °C for 6 h have the best crystallinity and the calculated crystallite size was in the range of 6–13 nm. The thermal analysis and FTIR spectra indicate a core–shell structure of the MFe₂O₄ nanoparticles obtained.     

Synthesis of textured Bi5Ti3FeO15 and LaBi4Ti3FeO15 ferroelectric layered Aurivillius phases by molten-salt flux methods

The ferroelectric layered Bi₅Ti₃FeO₁₅ and LaBi₄Ti₃FeO₁₅ Aurivillius phases were synthesized in high purity and textured microstructures in a molten Na₂SO₄/K₂SO₄ (1:1 molar ratio) flux in much shortened reaction times, 1 h minimum compared to conventional techniques. The particle growth and microstructure of both phases were investigated as a function of temperature and reaction duration, and yielded plate-like particles that could be synthesized in sizes from <1 μm to >20 μm. The product crystallinity, purity and microstructures were characterized via powder X-ray diffraction and scanning electron microscopy. The UV–vis diffuse reflectance of the products were measured and analyzed with respect to the resultant particle sizes.     

Hydrothermal synthesis of single-crystal VO2(B) nanobelts

Single crystalline VO₂(B) nanobelts with a metastable structure were obtained through a simple hydrothermal synthetic method. The VO₂(B) nanobelts were characterized by means of X-ray diffraction, transmission electron microscopy, selected area electronic diffraction, field-emission scanning electron microscopy and X-ray energy-dispersive spectroscopy techniques. The as-obtained VO₂(B) nanobelts are 400–600 nm long, typically 100–150 nm wide and 20–30 nm thick. The belt-like VO₂(B) with a high surface area may be beneficial to lithium insertion between the VO₆ layers for application in batteries.     

Characterization and synthesis of KTa0.1Nb0.9O3 particles via high temperature mixing method under hydrothermal conditions

KTa_0.1Nb_0.9O₃ (KTN) particles with an orthorhombic perovskite structure have been synthesized via a high temperature mixing method (HTMM) under hydrothermal conditions. The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and high-resolution transmission electron microcopy (HRTEM). The influence of alkaline concentration and solvent composition on the phase structure and morphology of the obtained powders was investigated. The results show that the well-crystallized KTN powders with sizes of 200–500 nm are successfully prepared at temperatures as low as 240 °C when the KOH concentration is 2.0 M and the isopropanol/water (I/W) volume ratio equals to 100/0.     

Hydrothermal synthesis,crystal structure and characterization of LiCoP5O14·H2O: A new condensed layered penta phosphate crystals

A new family of condensed hydrated lithium cobalt penta phosphate (LiCoP₅O₁₄·H₂O) crystals were synthesized by hydrothermal technique and characterized by X-ray diffraction method. The compound crystallizes in monoclinic system with space group P21/c and cell parameters a = 10.788(4) Å, b = 9.761(3) Å, c = 9.788(5) Å, β = 101.249(1) Å, Z = 4, exhibiting layer type polymeric structure. DTA study indicates that this compound has low thermal stability and magnetically frequency dependent paramagnetic behaviour.