Nannan Wu

Facile Synthesis of Porous Nickel/Carbon Composite Microspheres with Enhanced Electromagnetic Wave Absorption by Magnetic and Dielectric Losses.

Porous nickel/carbon (Ni/C) composite microspheres with diameters of ca. 1.2-1.5 μm were fabricated by a solvothermal method combined with carbon reduction. The pore size of the synthesized Ni/C composite microspheres ranged from several nanometers to 50 nm. The porous Ni/C composite microspheres exhibited a saturation magnetization (MS) of 53.5 emu g(-1) and a coercivity (HC) of 51.4 Oe. When tested as an electromagnetic (EM) wave absorption material, the epoxy resin composites containing 60% and 75% porous Ni/C microspheres provided high-performance EM wave absorption at thicknesses of 3.0-11.0 and 1.6-7.0 mm in the corresponding frequency ranges of 2.0-12 and 2.0-18 GHz, respectively. The superior EM wave absorption performances of porous Ni/C composite microspheres were derived from the synergy effects generated by the magnetic loss of nickel, the dielectric loss of carbon, and the porous structure.

Porous ternary TiO2/MnTiO3@C hybrid microspheres as anode materials with enhanced electrochemical performances

Porous TiO2/Mn3O4 nanocomposite microspheres have been successfully fabricated through impregnating Mn2+ ions into the lab-made porous TiO2, followed by an annealing process. The carbon-coated TiO2 and MnTiO3 (TiO2/MnTiO3@C) ternary hybrid composites with a specific surface area of 40.0 m2 g−1 were obtained by carbonizing the pyrrole coated porous TiO2/Mn3O4 microspheres. The carbon coating with a thickness of 1–2 nm was deposited on the surface and inner wall of pores. Electrochemical tests demonstrated that the as-prepared TiO2/MnTiO3@C porous electrode materials possessed a reversible capacity of 402.6 mA h g−1 after 300 cycles at a current density of 100 mA g−1 and the capacities of 259.8, 237.3, 200.4, 150.5 and 103.3 mA h g−1 at the current densities of 100, 200, 400, 800, and 1600 mA g−1. The MnTiO3/TiO2@C porous composites exhibited superior cycling and rate performances, arising from the synergistic effect that was created by little volume variation of the TiO2 matrix, high capacity of MnTiO3 and good electrical conductivity of the carbon coating during the charge/discharge processes.

Improved electromagnetic wave absorption of Co nanoparticles decorated carbon nanotubes derived from synergistic magnetic and dielectric losses

In this study, we report a feasible way to synthesize carbon nanotube nanocomposites deposited with cobalt nanoparticles (20-30 nm) on the surface (Co/CNTs) to serve as an electromagnetic (EM) wave absorption material. EM absorption measurements indicated that epoxy resin composites with 20 wt% Co/CNTs exhibited an effective EM absorption (RL < -10 dB) in the frequency range of 2.5-20 GHz with an absorber thickness of 1.0 to 6.0 mm. A strong absorption peak (RL = -36.5 dB) appeared at 4.1 GHz as the thickness was 4.0 mm, and the absorption bandwidth (RL < -10 dB) was in the frequency range of 3.6-4.6 GHz. The electromagnetic loss research suggested that the superior EM absorption performances including a light weight, strong absorption, broad frequency scope, and thin thickness could be ascribed to the synergistic effect of magnetic loss from Co nanoparticles and the dielectric loss of CNTs, resulting in better impedance matching.

Fe3O4 nanoparticles encapsulated in multi-walled carbon nanotubes possess superior lithium storage capability

In this work, Fe3O4 nanoparticles are successfully introduced inside multi-walled carbon nanotubes (Fe3O4@MWNTs) by an innovative wet chemical injection method. As anode materials for lithium-ion batteries, the Fe3O4@MWNTs deliver a superior long-term specific capacity of 703.7 mA h g−1 after 350 cycles at a current density of 100 mA g−1. The high capacity of Fe3O4 and the distinctive conductive network of cross-linked MWNTs are believed to boost the electrochemical capacity and rate capability. More importantly, the unique encapsulated structure is designed to efficiently cushion the strain induced by volume change during lithiation/delithiation processes. At the same time, size of the Fe3O4 nanoparticles was controlled and they were prevented from agglomerating by the restriction effect of the nanoscaled tube. Both features ensure the structural integrity of the electrode and the stable performance in long-term cycling tests.

Facile synthesis of porous Fe2TiO5 microparticulates serving as anode material with enhanced electrochemical performances

Porous iron titanium oxide (Fe2TiO5) microparticulates have been successfully synthesized via a facile hydrothermal route followed by a subsequent calcination process. Polyvinyl-pyrrolidone (PVP), serving as a surfactant, played a pivotal role in controlling the size and inducing the mesoporous structure of Fe2TiO5. The measured specific surface area is 83.1 m2 g−1 and the dominant pore size is ca. 10 nm. When tested as the anode material of lithium-ion batteries (LIBs), the as-prepared porous Fe2TiO5 microparticulates delivered a high reversible capacity of 468.3 mA h g−1 after 100 cycles at a current density of 100 mA g−1, which nearly quadrupled that of porous TiO2 microspheres and doubled that of Fe2O3 nanoparticles. Moreover, the porous Fe2TiO5 microparticulates also showed more superior rate capability and long-term cycling stability with respect to TiO2 and Fe2O3 samples. Even after the rate performance test, a high discharge capacity of 234.1 mA h g−1 was still maintained at a current density of 500 mA g−1 over another 250 cycles. The improved electrochemical performances are mainly attributed to the synergistic effect of TiO2 and Fe2O3 in Fe2TiO5, as well as the mesoporous structure.

Synthesis of strontium hexaferrite nanoplates and the enhancement of their electrochemical performance by Zn2+ doping for high-rate and long-life lithium-ion batteries

Hexagonal structured strontium hexaferrite (SrFe12O19) nanoplates with diameters of ca. 0.6–2.5 μm and thicknesses of 40–60 nm have been successfully synthesized by adjusting the Fe/Sr ratios via a solvothermal process followed by annealing. Zn2+-Doped strontium hexaferrite nanoplates were fabricated as above, except that zinc was also added. The as-prepared Zn2+-doped SrFe12O19 and SrFe12O19 nanoplates were then evaluated as anode materials for lithium-ion batteries (LIBs) for the first time. The electrochemical measurements showed that both the Zn2+-doped SrFe12O19 and SrFe12O19 nanoplates had high reversible capacities of 1015.8 mA h g−1 and 456.5 mA h g−1, respectively, after 270 cycles at a current density of 100 mA g−1. In addition, both samples exhibited good high-rate cycling performances; in particular, the Zn2+-doped SrFe12O19 nanoplates delivered 457.6 mA h g−1 at a high current density of 500 mA g−1 after 700 cycles. Therefore, strontium hexaferrites could be investigated as a candidate for long-life lithium-ion batteries. The superior cycling performances exhibited by Zn2+-doped SrFe12O19 are ascribed to the zinc-doping, which can efficiently enhance the electronic conductivity and improve the lithium ion diffusion of SrFe12O19; this was confirmed by impedance measurements.