Materials Science Forum Vol. 722

Abstract: In this paper, to improve the elevated temperature performance of spinel LiMn2O4 as cathode materials, the cation/anion co-doping and surface modification together were adopted. The SiO2 coated Li1.02Co0.1Mn1.9O4−xSx spinels were synthesized by the solid-state reaction method and Sol-gel coating process. The samples are characterized by XRD, SEM, galvanostatic charge-discharge. The results show that the Li1.02Co0.1Mn1.9O3.98S0.02 exhibits the best initial discharge capacity of 122mAh/g, and capacity retention rate gets to 92% after 100 cycles at room temperature (25 °C). The substitution of Co and S for Mn and O in LiMn2O4 can enhance the crystal structure stability and overcomes the Jahn-Teller distortion, but cannot resolve the elevated temperature cycling issue of the spinel cathode materials. The capacity loss of Li1.02Co0.1Mn1.9O3.98S0.02 without SiO2 coating gets to 38% after 50 cycles, whereas the 2.0wt.% SiO2-coated Li1.02Co0.1Mn1.9O3.98S0.02 cathode material has only 5.0% capacity loss after 50 cycles at elevated temperature (55°C). It indicates that nano SiO2 coating could suppress Mn dissolution in the electrolyte during cycles. So combining cation/anion co-doping and surface modification is best way to improve the elevated temperature cycling performance of spinel LiMn2O4 as cathode materials.

Abstract: A LiFePO₄/porous carbon nanocomposite was synthesized by using spontaneous precipitation combined with solid-state reaction. The microstructure, morphology and electrochemical properties of as-prepared samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), differential thermal analysis (TGA) and charge-discharge cycling tests. The results reveal that LiFePO₄ particles are well-dispersed into porous carbon framework. The initial discharge of nanocomposite is 143 mAh g^-1 at 0.1 C and 114 mAh g^-1 at 1 C with satisfactory capacity retention. The superior electrochemical performance of the composites can be attributed to the nano-confined effect of conducting porous carbon and the nano-size of LiFePO₄ particles in LiFePO4/porous carbon nanocomposite.

Abstract: Effects of hexadecyl trimethyl ammonium bromide (CTAB), polyethylene glycol nanowire (NPEG) and their nanocomposite additives on corrosion inhibition of Zn in 1 mol/L ZnSO4 solution were investigated by weight-loss measurements, electrochemical tests，scanning electron microscopy and battery discharge tests. The results show that the inhibition efficiency of nanocomposite additives is 70%, which is much higher than individual inhibitors of CTAB or NPEG alone, because of the notable synergistic effect between CTAB and NPEG. While CTAB can cause a negative shift of corrosion potential of zinc, NPEG can form a very thick hydrophobic layer on the surface of zinc electrode by adsorption. Furthermore, NPEG can render part of CTAB cations to form large micelle particles along the NPEG macromolecular chains and cross-link with NPEG, and thus greatly enhance the blocking effect of the hydrophobic layer. Therefore，the corrosion inhibition efficiency of the composite additives is much higher. The battery containing 0.05% CTAB and 0.05% NPEG performs better than the batteries with individual additives, especially at high discharge current rate.

Abstract: Polyaniline (PANI) and ordered macroporous carbon (C80) composites were prepared via a simple and speedy polymerization of aniline in the presence of C80. The effect of PANI content on the electrochemical properties was studied in detail. The morphologies were manifested through field emission scanning electron microscopy (FE-SEM), and the electrochemical properties were investigated by cyclic voltammetry (CV), galvanostatic charge-discharge and impedance in 1 mol/L H₂SO₄. The results indicate that the polymerization of aniline occurred in the pores of carbon, and as the aniline content increased, more polyaniline was synthesized in the pores. When the PANI content was 43 wt%, the specific capacitance of the composite was as high as 368.7 F/g at a current density of 0.06 A/g, which was 2.6 times higher than that of the host C80 (140 F/g).

Abstract: A magnetite composite composed of the organic compounds and Fe₃O₄ nanoparticles was prepared with microemulsion method. The Tween 80 and ammonia were used as surfactant and reducing agent, respectively, in synthesizing the Fe₃O₄ nanoparticles. The experimental results showed that the composite possessed good stability while the volume ratio of Tween 80 to butanol was 0.4 and the molar ratio of NH₄OH to Fe³⁺ was 14.6. The saturation magnetization of the composite depends on the molar ratio of NH₄OH to Fe³⁺. The mechanism of this stable Fe₃O₄ paste was realized by the Fe₃O₄ nanocomposite film using TEM. The microstructures of the film show that the magnetic nanoparticles in the composite are surrounded by Tween 80, which separates the magnetic nanoparticles and leads to good stability.

Abstract: Magnetic composites, especially ferrite composites, are of great interest for embedded inductor applications. In this paper, the Ni-Zn ferrite particles (Ni1-xZnxFe2O4, x=0.2～0.8) with different zinc contents were synthesized via chemical coprecipitation method followed by modification with γ-glycidoxypropyl trimethoxysilane (KH-560). The particles were investigated by X-ray diffraction (XRD) and vibrating sample magnetometer (VSM). The results show that the prepared Ni1-xZnxFe2O4(x=0.2～0.7) have good spinel structures, higher saturation magnetization (35.18～77.69 emu/g) and smaller hysteresis hoops, while Ni0.2Zn0.8Fe2O4 grains exhibit some paramagnetic behaviors, such as almost zero hysteresis and non-saturated magnetization. Next Ni1-xZnxFe2O4 magnetic/epoxy composites with different volume fraction of ferrite were prepared and their magnetic performances at high frequencies were characterized by an Agilent E4991A impedance analyzer (USA). It is found that with zinc content in Ni1-xZnxFe2O4 increasing from 0.2 to 0.7, the real part of the complex permeability (μ′) of these composites increase first and then decrease with the frequency increasing gradually from 10 MHz to 1 GHz. Of all, the epoxy composites with filler of Ni0.6Zn0.4Fe2O4 or Ni0.5Zn0.5Fe2O4 ferrite show good frequency stability, and the composites including Ni0.4Zn0.6Fe2O4 ferrite have the highest permeability, and the maximal value at the frequency of 100 MHz is 5.55 when the volume faction is 42.75%. The imaginary part of the complex permeability (μ′′) of all magnetic composites is low For the Ni0.2Zn0.8Fe2O4/epoxy composites, they have very low real permeability (μ′～1) and imaginary permeability (μ″≤0.2).

Abstract: Urchinlike Ni particles with different spines were synthesized. The microstructures and morphologies of the resulting materials were investigated by X-ray diffraction and scanning electron microscopy. And the electromagnetic parameters of these urchinlike Ni were measured with vector network analyzer at 2-18 GHz frequency. The results indicate that the electromagnetic parameters are affected by morphologies of materials. The long urchin spines will lead to larger permittivity.

Abstract: Nanoparticles of bismuth ferrite (BiFeO3) were fabricated by high-pressure pulsed laser deposition method (PLD) on Pt-coated Si substrates. Effects of the ambient oxygen pressure during deposition (from 1 Torr to 15 Torr) were studied with respect to the microstructures and magnetic properties of the samples. It was found that as the pressure is higher than 5 Torr isolated nanoparticles are formed and the size of these nanoparticles decreases with the deposition pressure. All the nanoparticles exhibit ferromagnetic behavior and the magnetic coercive filed decreases with the particle size.

Abstract: The composites composed of micro-sized calcium copper titanate (CCTO) and nano-sized metallic nickel (Ni) fillers in the polyvinylidene fluoride (PVDF) matrix (Ni/CCTO/PVDF) were prepared, in which the filler content (volume fraction) of Ni and CCTO was set at 60 %. The impedance spectra and a serial equivalent circuit model consisting three RC units were used to investigate the behaviors of the Ni/CCTO/PVDF three-phase composite system near the percolation threshold. The real (Z′) and imaginary (Z″) parts of the impedance dramatically decreased as the Ni content was increased from 22% to 24% indicating a transition from an insulating to a conducting state. This transition process has been realized by the changes in the capacitance derived from the model, and the investigation has been carried out to clarify the release mechanism of the entrapped electrons at the interfaces.