Synthesis of high performance Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>/C cathode material by ultrasonic-assisted sol–gel method

A novel ultrasonic-assisted sol–gel method is proposed to prepare Li₃V₂(PO₄)₃/C cathode material. X-ray diffraction analyses show that both Li₃V₂(PO₄)₃/C(A) synthesized by the ultrasonic-assisted sol–gel method and Li₃V₂(PO₄)₃/C(B) synthesized by a traditional sol–gel method have monoclinic structure. Scanning electron microscopy images indicate that the Li₃V₂(PO₄)₃/C(A) composite has a more uniform morphology than that of the Li₃V₂(PO₄)₃/C(B) composite. In the voltage range of 3.0–4.3 V (vs. Li/Li⁺), the initial specific discharge capacities of the Li₃V₂(PO₄)₃/C(A) and Li₃V₂(PO₄)₃/C(B) samples are 129.8 and 125.9 mAh g⁻¹ at 1C rate (1C = 133 mA g⁻¹), respectively. Furthermore, at 2-C charge/10-C discharge rate, the specific discharge capacity of the Li₃V₂(PO₄)₃/C(A) composite retains 113.2 mAh g⁻¹ after 50 cycles, but the Li₃V₂(PO₄)₃/C(B) composite only presents a capacity of 94.8 mAh g⁻¹.     

Structural properties of composite cathode material LiFePO<Subscript>4</Subscript>–Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>

Composite cathode material LiFePO₄–Li₃V₂(PO₄)₃ is synthesized through a chemical reduction and lithiation using FeVO₄·xH₂O as both iron and vanadium sources. The structural properties of LiFePO₄–Li₃V₂(PO₄)₃ are investigated. X-ray diffraction results show the composite material containing olivine type LiFePO₄ and monoclinic Li₃V₂(PO₄)₃ phases. High-resolution transmission electron microscopy and energy-dispersive X-ray spectrometry results indicate that mutual doping effects take place between the LiFePO₄ and Li₃V₂(PO₄)₃ particles with V³⁺ doping the LiFePO₄ while Fe²⁺ dopes the Li₃V₂(PO₄)₃. LiFePO₄–Li₃V₂(PO₄)₃ nanocomposites are formed in the carbon webs. There is no structural compatibility between monoclinic (Li₃V₂(PO₄)₃) and olivine (LiFePO₄) domains in composite material LiFePO₄–Li₃V₂(PO₄)₃.     

A PEG-assisted rheological phase reaction synthesis of 5LiFePO<Subscript>4</Subscript>⋅Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>/C as cathode material for lithium ion cells

5LiFePO₄⋅Li₃V₂(PO₄)₃/C composite cathode material is synthesized by a polyethylene glycol (PEG)-assisted rheological phase method. As a surfactant and dispersing agent, PEG can effectively inhabit the aggregation of colloidal particles during the formation of the gel. Meanwhile, PEG will coat on the particles to play the role of carbon source during the sintering. The samples are characterized by X-ray diffraction (XRD), scanning electron microscopy, and electrochemical methods. XRD results indicate that the 5LiFePO₄⋅Li₃V₂(PO₄)₃/C composites are well crystallized and contain olivine-type LiFePO₄ and monoclinic Li₃V₂(PO₄)₃ phases. The composite synthesized at 650 °C exhibits the initial discharge capacities of 134.8 and 129.9 mAh g⁻¹ and the capacity retentions of 96.2 and 97.1 % after 50 cycles at 1C and 2C rates, respectively.     

XRD,impedance, and Mössbauer spectroscopy study of the Li<Subscript>3</Subscript>Fe<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> + Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> composite for Li ion batteries

The synthesis procedure of the Li₃Fe₂(PO₄)₃?+?Fe₂O₃ composite is presented. The monoclinic (A type) and hematite phases were detected by X-ray diffraction after the synthesis of the composite. The structural α–β (at a temperature of 460 K) and β–γ (at a temperature of 523 K) phase transitions in the composite were indicated by the anomalies of the electrical conductivity, dielectric permittivity, and changes of activation energies of conductivity. Two phase transitions have been detected in the Li₃Fe₂(PO₄)₃?+?Fe₂O₃ composite by ⁵⁷Fe Mössbauer spectroscopy: the phase transition in Li₃Fe₂(PO₄)₃ from the paramagnetic to antiferromagnetic phase at temperature T _N?=?29.5 K and the Morin phase transition in Fe₂O₃ at temperature T _M?=?235 K.     

Synthesis,structural characterization and ionic conductivity of NASICON-type Ba<Subscript>x/2</Subscript>Li<Subscript>1-x</Subscript>Ti<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> (0.4 ≤ x ≤ 1) materials

The NASICON series, with formula Ba_x/2Li_1-xTi₂(PO₄)₃ (0.4 ≤ x ≤ 1), has been prepared by solid-state reaction and characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), Raman, nuclear magnetic resonance (NMR) and impedance spectroscopy (IS). XRD patterns of samples indicated the formation of single phases with rhombohedral structure (space group R-3c). The Rietveld analysis of XRD patterns was performed to deduce location of Li and Ba ions. FTIR, Raman, and NMR techniques showed the only presence of isolated PO₄ groups in analyzed phosphates. ³¹P MAS-NMR spectra were used to investigate Li and Ba distribution and ⁷Li MAS-NMR spectra to discriminated Li ions with different mobility in conduction paths. A maximum total conductivity of 2.5 × 10^?7 S cm^?1 and a minimum activation energy of 0.47 eV were obtained at room temperature for Ba_0.3Li_0.4Ti₂(PO₄)₃ (x = 0.6).     

Synthesis and characterization of oxide cathode materials of the system (1-x-y)LiNiO<Subscript>2</Subscript>·xLi<Subscript>2</Subscript>MnO<Subscript>3</Subscript>·yLiCoO<Subscript>2</Subscript>

Composite cathode materials produced by integrating isostructural (2D-layered) compounds LiNiO₂, LiCoO₂, and Li₂MnO₃ (Li(Li_1/3Mn_2/3)O₂) have been investigated utilizing a compositional phase diagram. The samples were characterized by multiple techniques to establish structure–property relationships. Specifically, for structural characterization, powder X-ray diffraction, scanning electron microscopy, thermo-gravimetric analysis, and X-ray photoelectron spectroscopy were carried out. For properties, electrochemical characterization was carried out. The best composition showed a discharge capacity of 244 mAh/g (C/15 rate) in the testing range of 4.6–2 V, with good coulombic efficiency and cyclability.     

Synthesis and characterization of “mulberry”-like Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/multiwalled carbon nanotube nanocomposites

Nanocomposites composed of multi-wall carbon nanotubes (MWNTs) and Fe₃O₄ nanoparticles were fabricated using solvothermal method. Transmission and scanning electron microscopy, energy dispersive spectroscopy, and X-ray powder diffraction measurements confirmed that these mulberry-like Fe₃O₄ microparticles which were combined with the MWNTs in a random pattern are constructed with tiny nanocrystallites (12 nm in average diameter). The magnetic properties of the Fe₃O₄/MWNTs nanocomposites were measured using a vibrating sample magnetometer. Results showed that the Fe₃O₄/MWNTs nanocomposites exhibited superparamagnetism at room temperature and possessed a lower saturation magnetization (around 27.6 emu/g) than that of the pure Fe₃O₄ nanoparticles (around 33.7 emu/g). The Fe₃O₄/MWNTs nanocomposites have potential applications in engineering and medicine.     

Preparation,structure and properties of La<Subscript>0.67</Subscript>Pb<Subscript>0.33</Subscript>(Mn<Subscript>1-x</Subscript>Co<Subscript>x</Subscript>)O<Subscript>3-δ</Subscript>

La_0.67Pb_0.33(Mn_1-xCo_x)O_3-δ ceramics with x=0, 0.01, 0.03, 0.06, 0.1 and 0.15 have been prepared in a two-step procedure. Precursor gels were made by the wet chemical malic acid method. The gels were calcined and then converted into ceramics by heat treatment at 950 °C and 1000 °C in air. X-ray diffraction showed that the compounds were phase pure. The crystal structure symmetry of the compounds was confirmed to be rhombohedral (space group R3̄c) for the whole investigated range of x. All compounds undergo a paramagnetic–ferromagnetic phase transition between 335 K and 225 K. The basic magnetic characteristics such as the Curie temperature , the paramagnetic Curie temperature θ, the effective magnetic moment and the saturated magnetization decrease with increasing Co doping. The ferromagnetic transition is accompanied by an anomaly in the electrical resistance for all compounds. The high-temperature insulator–metal transitions () do not coincide with the relevant . A large magnetoresistance peak of about 15% was observed for all compounds at . PACS 72.80.Ga; 75.47.Lx; 75.60.Ej     

Synthesis and characterization of LiNi<Subscript>y</Subscript>Co<Subscript>1−y</Subscript>PO<Subscript>4</Subscript> (y=0–1) cathode materials for lithium secondary batteries

In this work series of LiNi_yCo_1−yPO₄ (y=0, 0.2, 0.4, 0.6, 0.8 and 1) phospho olivines were synthesized by solution co-precipitation technique and characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) and impedance spectroscopic analysis. The XRD patterns of LiNi_yCo_1−yPO₄ (y=0.2, 0.4, 0.6 and 0.8) revealed that they are essentially single phase and have an Olivine-type XRD patterns similar to those of their parent compounds LiCoPO₄ and LiNiPO₄. An increase in wave number for most of the dominant infrared bands in PO₄ vibrational region for the substitution of Co by Ni in LiCoPO₄ indicated the strengthening of both the P-O and Li/Ni-O bonds. Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003.     

Sol–gel synthesis and characterization of Li<Subscript>2</Subscript>CO<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> composite solid electrolytes

Composite solid electrolytes in the system (1???x)Li₂CO₃–xAl₂O₃, with x?=?0.0–0.5 (mole), were synthesized by a sol–gel method. The synthesis carried out at low temperature resulted in voluminous and fluffy products. The obtained materials were characterized by X-ray diffraction, differential scanning calorimetry, scanning electron microscopy/energy-dispersive X-ray, Fourier transform infrared spectroscopy and AC impedance spectroscopy. Structural analysis of the samples showed an amorphous feature of Li₂CO₃ and traces of α-LiAlO₂, γ-LiAlO₂ and LiAl₅O₈. The prepared composite samples possess high ionic conductivities at 130–180 °C on account of the presence of lithium aluminates as well as the formation of a high concentration of an amorphous phase of Li₂CO₃ via this sol–gel preparative technique.     

Specific heat of the [NH<Subscript>2</Subscript>(CH<Subscript>3</Subscript>)<Subscript>2</Subscript>]<Subscript>2</Subscript>ZnCl<Subscript>4</Subscript> crystal in the temperature region 80–300 K

The specific heat of [NH₂(CH₃)₂]₂ZnCl₄ was measured calorimetrically in the temperature region 80–300 K. As the temperature T decreases, the C _p (T) dependence indicates a phase transition sequence, with the phase transition at T₆=151 K observed for the first time. The thermodynamic characteristics of the crystal were refined. The transformation occurring at T₂=298.3 K is shown to be an incommensurate-commensurate phase transition.     

Spectroscopic analysis of Pr<Superscript>3+</Superscript> crystal-field transitions in YAl<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript>

Yttrium aluminium borate single crystals, doped with 1 and 4 mol% of Pr³⁺, were analyzed in the wave number range 500–25000 cm⁻¹ and temperature range 9–300 K by means of high-resolution Fourier transform spectroscopy. In spite of the complex spectra, exhibiting broad and split lines, the energy level scheme was obtained for several excited manifolds. The careful analysis of the spectra as a function of the temperature allowed us to identify most of the sublevels of the ground manifold. The thermally induced line shift, well described by a single-phonon coupling model, could be exploited to provide information about the energy of the phonons involved. The orientation of the dielectric ellipsoid and of the dipole moments associated to a few transitions was also determined from linear dichroism measurements. The experimental data were fitted in the framework of the crystal-field theory, but the agreement was not satisfactory, as already reported for Pr³⁺ ion in other matrices. Additional discrepancies came from the dichroic spectra analysis and the line splitting, possibly associated to hyperfine interaction. Some causes which might be responsible for the difficulties encountered in the Pr³⁺ ion theoretical modelling are discussed.     

Lithium conductivity and lithium diffusion in NASICON-type Li<Subscript>1+x</Subscript>Ti<Subscript>2–x</Subscript>Al<Subscript>x</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> (x= 0; 0.3) prepared by mechanical activation

LiTi₂(PO₄)₃ (LTP) and Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) (S. g. R-3c) have been prepared using conventional ceramic and mechanical activation (MA) methods. It has been shown that preliminary mechanical activation of initial mixtures leads to different nature and amount of dielectric admixtures in the final product after heat treatment at 800–1000 °C as compared with ceramic method. Transport properties of as prepared materials have been studied by lithium ionic conductivity at d.c. and a.c. (complex impedance method), and ⁷Li NMR spin-lattice relaxation rate T₁ ^–1 measurements. Lithium ionic conductivity of mechanochemically prepared LTP and LATP was characterized by significant reduction of grain boundary resistance, especially for LTP, while the bulk conductivity and Li ion diffusion does not noticeably change. The activation energy of bulk conductivity and Li ion diffusion, i.e. short-range motion, appeared to be almost the same for all samples and was equal to ~0.20 eV. On contrary, the activation energy of d.c.-conductivity, i.e. long-range Li ion motion decreases from ~0.6 eV for ceramic samples to ~0.4 eV for samples prepared via mechanochemical route. It was proposed that MA leads to formation of nano-particulate high-conductive grain boundaries both in LTP and LATP. Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15, 2007.     

The differentiation of elementary polarizations of FeF<Subscript>3</Subscript>·3H<Subscript>2</Subscript>O/C cathode material in LIB

Time-dependent elementary polarizations of FeF₃·3H₂O/C cathode material were quantitatively investigated in dc polarization in order to determine the key factors that comprise the total polarization. The measurement of electrochemical impedance spectrum at a given state of charge and the subsequent least square fitting of its equivalent circuit allow the calculation of elementary contributions of individual kinetic step to the total polarization. The profiles of the calculations were well consistent with those of experiments based on the same states of charge, and the elementary contributions could be differentiated successfully which reveal that the solid-state diffusion process makes the largest contribution to the total polarization after 2.5 s discharge beginning with open-circuit voltage (OCV) level 3.5 V. The results may be helpful for the design of batteries of better performance with FeF₃ cathode.     

Thin <Emphasis Type="Italic">W</Emphasis>′ and <Emphasis Type="Italic">W</Emphasis> domain walls in ferroelastic Pb<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>

A model of ferroelastic domain walls consisting of matching interlayers of crystal lattices is proposed. The dependences of the parameters of the interlayers and of the parameters of the equations for W′ and W domain walls on the crystal lattice parameters of the ferroelastic phase in Pb₃(PO₄)₂ are determined. The problem concerning the number of possible orientational states and their interaction in a polydomain crystal is considered.     

Preparation and characterization of organic–inorganic hybrid compound [N(C<Subscript>4</Subscript>H<Subscript>9</Subscript>)<Subscript>4</Subscript>]<Subscript>2</Subscript>Cu<Subscript>2</Subscript>Cl<Subscript>6</Subscript>

Organic–inorganic hybrid sample [N(C₄H₉)₄]₂Cu₂Cl₆ was prepared via the reaction between copper chloride and tetrabutylammonium chloride. The compound was characterized by X-ray powder diffraction, IR, Raman, differential scanning calorimetry (DSC), DTA-TGA analysis and electrical impedance spectroscopy. DSC studies indicate a presence of one-phase transition at 343 K. The complex impedance of compound [N(C₄H₉)₄]₂Cu₂Cl₆ have been investigated in temperature and frequency ranges 300–380 K and 200 Hz–5 MHz, respectively. The Z′ and Z″ versus frequency plots are well fitted to an equivalent circuit model. The circuits consist of the parallel combination of bulk resistance R _p and constant phase elements CPE. The frequency dependence of the conductivity is interpreted in term of Jonscher's law: s(w) = s_dc + Awⁿ \sigma (\omega ){ } = {\sigma_{\rm{dc}}} + { }A{\omega^n} . The conductivity follows the Arrhenius relation. The variation of the value of these elements with temperatures confirmed the availability of the phase transition at 343 K detected by DSC and electrical measurements.     

Controlled flame synthesis of αFe<Subscript>2</Subscript>O<Subscript>3</Subscript> and Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles: effect of flame configuration,flame temperature,and additive loading

Superparamagnetic iron oxide nanoparticles are used in diverse applications, including optical magnetic recording, catalysts, gas sensors, targeted drug delivery, magnetic resonance imaging, and hyperthermic malignant cell therapy. Combustion synthesis of nanoparticles has significant advantages, including improved nanoparticle property control and commercial production rate capability with minimal post-processing. In the current study, superparamagnetic iron oxide nanoparticles were produced by flame synthesis using a coflow flame. The effect of flame configuration (diffusion and inverse diffusion), flame temperature, and additive loading on the final iron oxide nanoparticle morphology, elemental composition, and particle size were analyzed by transmission electron microscopy (TEM), high-resolution TEM (HR-TEM), energy dispersive spectroscopy (EDS), and Raman spectroscopy. The synthesized nanoparticles were primarily composed of two well known forms of iron oxide, namely hematite αFe₂O₃ and magnetite Fe₃O₄. We found that the synthesized nanoparticles were smaller (6–12 nm) for an inverse diffusion flame as compared to a diffusion flame configuration (50–60 nm) when CH₄, O₂, Ar, and N₂ gas flow rates were kept constant. In order to investigate the effect of flame temperature, CH₄, O₂, Ar gas flow rates were kept constant, and N₂ gas was added as a coolant to the system. TEM analysis of iron oxide nanoparticles synthesized using an inverse diffusion flame configuration with N₂ cooling demonstrated that particles no larger than 50–60 nm in diameter can be grown, indicating that nanoparticles did not coalesce in the cooler flame. Raman spectroscopy showed that these nanoparticles were primarily magnetite, as opposed to the primarily hematite nanoparticles produced in the hot flame configuration. In order to understand the effect of additive loading on iron oxide nanoparticle morphology, an Ar stream carrying titanium-tetra-isopropoxide (TTIP) was flowed through the outer annulus along with the CH₄ in the inverse diffusion flame configuration. When particles were synthesized in the presence of the TTIP additive, larger monodispersed individual particles (50–90 nm) were synthesized as observed by TEM. In this article, we show that iron oxide nanoparticles of varied morphology, composition, and size can be synthesized and controlled by varying flame configuration, flame temperature, and additive loading.     

Spectroscopic study of magnetic phase transitions in Nd<Subscript>x</Subscript>Gd<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript>

Magnetic ordering and spin reorientation in iron borates Nd_xGd_1?xFe₃(BO₃)₄ (x = 0.01, 0.04, 0.25, 1.0) are studied using a rare-earth spectroscopic probe.     

<Superscript>2</Superscript>H NMR investigation of the transition to the proton glass state in the Cs<Subscript>5</Subscript>H<Subscript>3</Subscript>(SO<Subscript>4</Subscript>)<Subscript>4</Subscript> · 0.5H<Subscript>2</Subscript>O crystal

A crystal of the Cs₅H₃(SO₄)₄ · xH₂O (x ≈ 0.5) (PCHS) compound, which belongs to the family of proton conductors with a complex system of hydrogen bonds, is investigated by ²H NMR spectroscopy. The temperature and orientation dependences of the ²H NMR spectra are measured and analyzed. It is established that, upon transition to the glassy phase at the temperature T _g = 260 K, the parameters characterizing the proton exchange between positions in hydrogen bonds remain unchanged to within the limits of experimental error. The protons in the two-dimensional network of hydrogen bonds in the (001) plane are dynamically disordered over possible positions down to temperatures considerably lower than the glass transition point T _g . However, water molecules are fixed at particular structural positions in the phase transition range. In PCHS crystals with a nonstoichiometric water content, this circumstance can be responsible for the frustration that leads to the formation of the glassy state.