Yu-Jun Bai

In situ synthesis of one-dimensional MWCNT/SiC porous nanocomposites with excellent microwave absorption properties

One-dimensional multiwalled carbon nanotube (MWCNT)/SiC porous nanocomposites were prepared via an in situ reaction between Si and MWCNTs induced by the reaction between Na and I2. The as-prepared nanocomposites exhibit outstanding microwave absorbing performances with an absorber thickness of about 2 mm. The absorbing bandwidth for the nanocomposites increases by raising the reaction temperature from 200 to 400 °C. The dielectric polarizations, which originate from the synergistic effect of the defects, porous structures and nanoparticles in the nanocomposites, are responsible for the excellent microwave absorbing performances.

Yttrium-modified Li4Ti5O12 as an effective anode material for lithium ion batteries with outstanding long-term cyclability and rate capabilities

Yttrium-modified Li4Ti5O12 (YLTO) was fabricated by a coprecipitation method using tetrabutyl titanate, Y(NO3)3·6H2O and LiOH·H2O as reactants, followed by simply sintering the dried mixture at 600 °C. The products and their lithiation–delithiation process were characterized by a combination of electrochemical measurements, X-ray diffraction, transmission electron microscopy and nitrogen adsorption. The YLTO exhibits excellent long-term cycling stability (over 1000 cycles) at a high current rate of 10 C and outstanding rate capabilities. Particularly, the YLTO demonstrates remarkable cyclability even if directly cycled at a rate of 10 C without low-rate activation and with no relaxation between charge and discharge. Even without utilizing carbon black as conductive material, the YLTO still shows prominent rate capabilities and long-term cyclic performance at a rate of 5 C. The excellent performance is ascribed to the increased lattice constant, improved electronic and ionic conductivities, refined grains with large surface area and uniform nanopores resulting from the Y-modification.

Excellent long-term cycling stability of La-doped Li4Ti5O12 anode material at high current rates

La-doped Li4Ti5O12 (LLTO) was prepared by a simple approach using tetrabutyl titanate, LiOH·H2O and La(NO3)3·6H2O as raw materials, followed by sintering the dried mixture at 600 °C for 5 h. Without requiring any further treatments, the as-obtained LLTO could exhibit excellent long-term cycling stability, high coulombic efficiency close to 100% at various charge–discharge rates, outstanding capacity retention at high current rates of 10–50 C, remarkable performance in the temperature range from −40 to 60 °C, good cycling performance even subjected to overcharging to about 10 times of the reversible capacity. The La-doped LTO could be directly used as efficient anode materials for lithium-ion batteries.

Experimental and theoretical investigation on the high frequency dielectric properties of Ag/Al2O3 composites

The impedance and dielectric properties of Ag/Al2O3 composites are investigated experimentally in the frequency range from 100 MHz to 1 GHz. Besides, equivalent circuit analysis and numerical simulations were carried out. For the composites with sufficiently high silver loading, current paths were formed and negative permittivity appeared. The negative permittivity can be well described by lossy Drude model. Moreover, the negative permittivity sample manifests inductive characteristic and shunt inductors are added to its equivalent circuit. Numerical simulations show that the interconnection of silver particles results in negative permittivity, hence the serious attenuation of electromagnetic waves.

Preparation of InN nanocrystals by solvo-thermal method

Abstract Indium nitride (InN) nanocrystals were successfully prepared by the reaction of InCl 3 and Li 3 N at 250°C with xylene as the solvent. X-ray powder diffraction and TEM observation showed that the two phases of cubic InN and hexagonal InN coexist in the nanocrystals prepared by the solvo-thermal method.

Carbon-coated Fe-Mn-O composites as promising anode materials for lithium-ion batteries.

Fe-Mn-O composite oxides with various Fe/Mn molar ratios were prepared by a simple coprecipitation method followed by calcining at 600 °C, and carbon-coated oxides were obtained by pyrolyzing pyrrole at 550 °C. The cycling and rate performance of the oxides as anode materials are greatly associated with the Fe/Mn molar ratio. The carbon-coated oxides with a molar ratio of 2:1 exhibit a stable reversible capacity of 651.8 mA h g(-1) at a current density of 100 mA g(-1) after 90 cycles, and the capacities of 567.7, 501.3, 390.7, and 203.8 mA h g(-1) at varied densities of 200, 400, 800, and 1600 mA g(-1), respectively. The electrochemical performance is superior to that of single Fe3O4 or MnO prepared under the same conditions. The enhanced performance could be ascribed to the smaller particle size of Fe-Mn-O than the individuals, the mutual segregation of heterogeneous oxides of Fe3O4 and MnO during delithiation, and heterogeneous elements of Fe and Mn during lithiation.

Enhanced electrochemical performance of FeWO4 by coating nitrogen-doped carbon.

FeWO4 (FWO) nanocrystals were prepared at 180 °C by a simple hydrothermal method, and carbon-coated FWO (FWO/C) was obtained at 550 °C using pyrrole as a carbon source. The FWO/C obtained from the product hydrothermally treated for 5 h exhibits reversible capacities of 771.6, 743.8, 670.6, 532.6, 342.2, and 184.0 mAh g(-1) at the current densities of 100, 200, 400, 800, 1600, and 3200 mA g(-1), respectively, whereas that from the product treated for 0.5 h achieves a reversible capacity of 205.9 mAh g(-1) after cycling 200 times at a current density of 800 mA g(-1). The excellent electrochemical performance of the FWO/C results from the combination of the nanocrystals with good electron transport performance and the nitrogen-doped carbon coating.

Microwave absorption properties of MWCNT-SiC composites synthesized via a low temperature induced reaction

The composites containing SiC and multiwalled carbon nanotubes (MWCNTs) were synthesized via the reaction of Si powders and MWCNTs induced by that of Na and sulfur. The MWCNT-SiC composites prepared at 600 °C exhibit excellent microwave absorbing properties, which reach a minimum reflection loss of -38.7 dB at a frequency around 12.9 GHz. The absorbing properties are bound up with the high yield of porous SiC spheres comprised of nanocrystals. The porous structure, high density of stacking faults in SiC crystallites, interfaces between MWCNTs and SiC spheres, grain boundaries between SiC nanocrystals, as well as the interfacial polarizations aroused therefrom, are responsible for the excellent microwave absorbing properties.

One step convenient synthesis of crystalline β-Si3N4

Well-crystallized β-Si3N4 was directly prepared at an initial reaction temperature of 150 °C through the reaction of SiCl4 and NaN3 in the presence of a small amount of CCl4. Characterization by X-ray diffraction, high-resolution electron microscopy, X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy indicates that the product synthesized is crystalline β-Si3N4. The yield of β-Si3N4 is about 86% based on the amount of precursor SiCl4 used at the initial reaction temperature of 150 °C, and is more than 90% at the reaction temperature of 200 °C with the product β-Si3N4 in high crystallinity. The dominant morphology of the product is short rods with the growth axis along the [001] direction. The formation mechanism of crystalline β-Si3N4 was discussed briefly, and the role of CCl4 in the formation process of β-Si3N4 was analyzed.

Ionic Conductor of Li2SiO3 as an Effective Dual-Functional Modifier To Optimize the Electrochemical Performance of Li4Ti5O12 for High-Performance Li-Ion Batteries

Ionic conductor of Li2SiO3 (LSO) was used as an effective modifier to fabricate surface-modified Li4Ti5O12 (LTO) via simply mixing followed by sintering at 750 °C in air. The electrochemical performance of LTO was enhanced by merely adjusting the mass ratio of LTO/LSO, and the LTO/LSO composite with 0.51 wt % LSO exhibited outstanding rate capabilities (achieving reversible capacities of 163.8, 157.6, 153.1, 147.0, and 137.9 mAh g-1 at 100, 200, 400, 800, and 1600 mA g-1, respectively) and remarkable long-term cycling stability (120.2 mAh g-1 after 2700 cycles with a capacity fading rate of only 0.0074% per cycle even at 500 mA g-1). Combining structural characterization with electrochemical analysis, the LSO coating coupled with the slight doping effect adjacent to the LTO surface contributes to the enhancement of both electronic and ionic conductivities of LTO.