Wenbo Jin

Expanded graphite embedded with aluminum nanoparticles as superior thermal conductivity anodes for high-performance lithium-ion batteries

The development of high capacity and long-life lithium-ion batteries is a long-term pursuing and under a close scrutiny. Most of the researches have been focused on exploring electrode materials and structures with high store capability of lithium ions and at the same time with a good electrical conductivity. Thermal conductivity of an electrode material will also have significant impacts on boosting battery capacity and prolonging battery lifetime, which is, however, underestimated. Here, we present the development of an expanded graphite embedded with Al metal nanoparticles (EG-MNPs-Al) synthesized by an oxidation-expansion process. The synthesized EG-MNPs-Al material exhibited a typical hierarchical structure with embedded Al metal nanoparticles into the interspaces of expanded graphite. The parallel thermal conductivity was up to 11.6 W·m−1·K−1 with a bulk density of 453 kg·m−3 at room temperature, a 150% improvement compared to expanded graphite (4.6 W·m−1·K−1) owing to the existence of Al metal nanoparticles. The first reversible capacity of EG-MNPs-Al as anode material for lithium ion battery was 480 mAh·g−1 at a current density of 100 mA·g−1, and retained 84% capacity after 300 cycles. The improved cycling stability and system security of lithium ion batteries is attributed to the excellent thermal conductivity of the EG-MNPs-Al anodes.

Hydrogen storage capacity of single-walled carbon nanotube prepared by a modified arc discharge

ABSTRACT Single-walled carbon nanotubes (SWCNTs, the mean diameter of 1.35 nm) were produced by a modified arc discharging furnace using a mixture powder of KCl and Co-Ni alloy as catalyst at 600°C. The hydrogen storage capacity of SWCNTs was enhanced by the mechanism of atom hydrogen spillover from the supported catalyst. The temperature effect on the hydrogen storage capacity of as-grown SWCNTs was investigated. The relative experiments of SWCNT hydrogen uptake and release were carried out by a high-pressure volumetric gas-adsorption measurement system. The experimental results indicated that the hydrogen storage capacity of SWCNTs increased with the environmental temperatures decreasing. The hydrogen storage capacity of SWCNTs was up to 1.73 wt% at 77 K for 2 hours under the pressure of 10 MPa, and the corresponding releasing hydrogen capacity is about 1.23 wt% under ambient pressure.

Direct in situ synthesis of a 3D interlinked amorphous carbon nanotube/graphene/BaFe12O19 composite and its electromagnetic wave absorbing properties

The 3D interlinked amorphous carbon nanotube (ACNT)/reduced graphene oxide (RGO)/BaFe12O19 (BF) composite was directly prepared by a self-propagation combustion process. The RGO was synthesized in situ through the massive heat release during the auto-combustion reaction. The interlinked ACNTs and graphene as well as BF formed the conductive networks for improving the dielectric and magnetic loss. The reflection loss peak of ACNT/RGO/BF composite was −19.03 dB at 11.04 GHz in the frequency range of 2–18 GHz. The frequency bandwidth of the reflection loss below −10 dB was 3.8 GHz. The 3D interlinked ACNT-RGO structure, which was composed of dense intertwined ACNT and graphene with quantities of dihedral angles, could consume incident waves via multiple reflections inside the 3D structures. The high conductivity of 3D interlinked ACNT/RGO networks would lead to energy dissipation in the form of heat through molecular friction and dielectric loss.

Preparation and electromagnetic wave absorbing properties of 3D graphene/pine needle-like iron nano-acicular whisker composites

The improvement of high reflection loss and broad frequency bandwidth for electromagnetic wave absorption materials is a long-term effort. The superb micro-structures of the absorber have significant impact on increasing reflection loss and broadening frequency bandwidth. Herein, we prepared 3D graphene by chemical vapor deposition and then 3D graphene/pine needle-like iron nano-acicular whisker composites were in situ synthesized by an electrochemical deposition process under an electric field using 3D graphene as substrate. The nano-acicular whiskers show different sizes and the mean diameter of the individual iron nano-acicular whiskers was about 150 nm. The saturation magnetization (MS) of the 3D graphene/iron nano-acicular whisker composite was about 42.65 emu g−1 and the coercivity (Hc) was 143 Oe, and it shows good magnetic properties. In the frequency range of 2–18 GHz, the reflection loss value of the graphene/iron nano-acicular whisker composites with a thickness of 2 mm could reach −12.81 dB at 10.95 GHz and the effective absorption bandwidth below −10 dB was 2.16 GHz. The nano-acicular whiskers could effectively improve the electromagnetic wave absorbing properties. The results suggested that the as-prepared graphene/iron nano-acicular whisker nanocomposite showed great potential applications as a new absorber material.

Self‐propagating Combustion Triggered Synthesis of 3D Lamellar Graphene/BaFe12O19 Composite and Its Electromagnetic Wave Absorption Properties

The synthesis of 3D lamellar graphene/BaFe12O19 composites was performed by oxidizing graphite and sequentially self-propagating combustion triggered process. The 3D lamellar graphene structures were formed due to the synergistic effect of the tremendous heat induced gasification as well as huge volume expansion. The 3D lamellar graphene/BaFe12O19 composites bearing 30 wt % graphene present the reflection loss peak at −27.23 dB as well as the frequency bandwidth at 2.28 GHz (< −10 dB). The 3D lamellar graphene structures could consume the incident waves through multiple reflection and scattering within the layered structures, prolonging the propagation path of electromagnetic waves in the absorbers.

In situ synthesis and electromagnetic wave absorbing properties of sandwich microstructured graphene/La-doped barium ferrite nanocomposite

The development of high reflection loss and broad frequency bandwidth for electromagnetic wave absorbing materials has been pursued for a long time. Constructing a rational microstructure of an absorber will have significant impact on reflection loss increase and frequency bandwidth broadening. Herein, we successfully prepare a sandwich microstructured graphene/BaFe12O19 nanocomposite by an in situ auto-combustion method. Compared to pure BaFe12O19, the sandwich microstructured graphene/BaFe12O19 showed better electromagnetic wave absorbing properties. Furthermore, the sandwich microstructured graphene/Ba0.8La0.2Fe12O19 nanocomposite was prepared with La-doped BaFe12O19 using the same method. The obtained graphene/Ba0.8La0.2Fe12O19 nanocomposite exhibited a saturation magnetization of 26.55 emu g−1 at room temperature and exhibited excellent magnetic performance. The maximum reflection loss of the sandwich microstructured graphene/Ba0.8La0.2Fe12O19 nanocomposite with a thickness of 1 mm could reach up to −40.26 dB, and a frequency bandwidth value below −10 dB was observed up to 3.87 GHz within the frequency range of 2–18 GHz.

Coral-like amorphous carbon nanotubes synthesized by a modified arc discharge

ABSTRACT A coral-like amorphous carbon nanotube was prepared by a modified arc discharging furnace in hydrogen atmosphere with a mixture of Mo-Co2O3-Mg powders as catalyst at 600°C. This carbon nanotube presented a microscopic coral-like by SEM observation and amorphous structure of nanotubes by HRTEM observation. The XRD diffraction and Raman pattern presented noncrystal characteristics compared to the normal graphite structure. We believed that these results may be affected by the “synergistic” effect of catalyst, atmosphere, and temperature in the synthesis process. The possible explanations to the formation mechanism of this novel carbon nanotube have also been proposed.