Wei-Li Song

Ferroferric Oxide/Multiwalled Carbon Nanotube vs Polyaniline/ Ferroferric Oxide/Multiwalled Carbon Nanotube Multiheterostructures for Highly Effective Microwave Absorption

Light-weight nanocomposites filled with carbon nanotubes (CNTs) are developed for their significant potentials in electromagnetic shielding and attenuation for wide applications in electronics, communication devices, and specific parts in aircrafts and vehicles. Specifically, the introduction of a second phase into/onto CNTs for achieving CNT-based heterostructures has been widely pursued due to the enhancement in either dielectric loss or magnetic loss. In this work, ferroferric oxide (Fe(3)O(4)) was selected as the phase in multiwalled carbon nanotube (MWCNT)-based composites for enhancing magnetic properties to obtain improved electromagnetic attenuation. A direct comparison between the two-phase heterostructures (Fe(3)O(4)/MWCNTs) and polyaniline (PANI) coated Fe(3)O(4)/MWCNTs, namely, three-phase heterostructures (PANI/Fe(3)O(4)/MWCNTs), was made to investigate the interface influences of Fe(3)O(4) and PANI on the complex permittivity and permeability separately. Compared to PANI/Fe(3)O(4)/MWCNTs, Fe(3)O(4)/MWCNTs exhibited enhanced magnetic properties coupled with increased dielectric properties. Interfaces between MWCNTs and heterostructures were found to play a role in the corresponding properties. The evaluation of microwave absorption of their wax composites was carried out, and the comparison between Fe(3)O(4)/MWCNTs and PANI/Fe(3)O(4)/MWCNTs with respect to highly efficient microwave absorption and effective absorption bandwidth was discussed.

Polymer/Boron Nitride Nanocomposite Materials for Superior Thermal Transport Performance

Boron nitride nanosheets were dispersed in polymers to give composite films with excellent thermal transport performances approaching the record values found in polymer/graphene nanocomposites. Similarly high performance at lower BN loadings was achieved by aligning the nanosheets in poly(vinyl alcohol) matrix by simple mechanical stretching (see picture).

High dielectric loss and its monotonic dependence of conducting-dominated multiwalled carbon nanotubes/silica nanocomposite on temperature ranging from 373 to 873 K in X-band

The dielectric properties of multiwalled carbon nanotubes/silica (MWNTs/SiO2) nanocomposite with 10 wt % MWNTs are investigated in the temperature range of 373–873 K at frequencies between 8.2 and 12.4 GHz (X-band). MWNTs/SiO2 exhibits a high dielectric loss and a positive temperature coefficient (PTC) of dielectric effect that complex permittivity increases monotonically with increasing temperature. The PTC effect on the dielectric constant is ascribed to the decreased relaxation time of interface charge polarization, and the PTC effect on the dielectric loss is mainly attributed to the increasing electrical conductivity. The loss tangent strongly supports the dominating contribution of conductance to the dielectric loss.

Hollow core-shell structured Si/C nanocomposites as high-performance anode materials for lithium-ion batteries.

Hollow core-shell structured Si/C nanocomposites were prepared to adapt for the large volume change during a charge-discharge process. The Si nanoparticles were coated with a SiO2 layer and then a carbon layer, followed by etching the interface SiO2 layer with HF to obtain hollow core-shell structured Si/C nanocomposites. The Si nanoparticles are well encapsulated in a carbon matrix with an internal void space between the Si core and the carbon shell. The hollow core-shell structured Si/C nanocomposites demonstrate a high specific capacity and excellent cycling stability, with capacity decay as small as 0.02% per cycle. The enhanced electrochemical performance can be attributed to the fact that the internal void space can accommodate the volume expansion of Si during lithiation, thus preserving the structural integrity of electrode materials, and the carbon shell can increase the electronic conductivity of the electrode.

Facile fabrication of ultrathin graphene papers for effective electromagnetic shielding

Ultrathin electromagnetic interference (EMI) shielding materials promise great application potential in portable electronic devices and communication instruments. Lightweight graphene-based materials have been pursued for their exclusive microstructures and unique shielding mechanism. However, the large thickness of the current low-density graphene-based composites still limits their application potential in ultrathin devices. In this work, a novel approach has been taken to use conductive graphene paper (GP) in the fabrication of ultrathin EMI shielding materials. The as-prepared flexible GPs exhibit highly effective shielding capabilities, reaching ∼19.0 dB at ∼0.1 mm in thickness and ∼46.3 dB at ∼0.3 mm in thickness, thus the thinnest GPs having the best shielding performance among graphene-based shielding materials. Double-layered shielding attenuators have been designed and fabricated for a high shielding performance of up to ∼47.7 dB at a GP thickness of ∼0.1 mm. Mechanistically, the high performance should be due to Fabry–Perot resonance, which is unusual in carbon-based shielding materials. The preparation of conductive GPs of superior shielding performance is relatively simple, amenable to large-scale production of ultrathin materials for EMI shielding and electromagnetic attenuators, with broad applications in lightweight portable electronic devices.

Rational design of graphene/porous carbon aerogels for high-performance flexible all-solid-state supercapacitors

Lightweight flexible energy storage devices have aroused great attention due to the remarkably increasing demand for ultrathin and portable electronic devices. As typical new two-dimensional carbon materials, graphene-based porous structures with ultra-light weight and exclusive electrochemical properties have demonstrated outstanding capacitive ability in supercapacitors. Thus far, the performance of all-solid-state supercapacitors achieved from graphene-based materials is still unsatisfactory. In this work, we have rationally designed graphene/porous carbon (GN/PC) aerogels via a simple green strategy to achieve flexible porous electrode materials. The ordered porous carbon (PC) with high specific surface area and good capacitance was introduced as a spacer to efficiently inhibit the restacking of graphene (GN) sheets, which significantly enhanced the specific surface area and facilitated the transport and diffusion of ions and electrons in the as-synthesized porous hybrid structure. The all-solid-state electrodes fabricated by the as-prepared GN/PC aerogels presented excellent flexibility, high specific capacitance and good rate performance in a polyvinyl alcohol/KOH gel electrolyte. Implication of the specific capacitances of ∼187 F g−1 at 1 A g−1 and 140 F g−1 at 10 A g−1 suggests that the GN/PC aerogels promise great potentials in the development of lightweight high-performance flexible energy storage devices.

Interfacial engineering of carbon nanofiber-graphene-carbon nanofiber heterojunctions in flexible lightweight electromagnetic shielding networks.

Lightweight carbon materials of effective electromagnetic interference (EMI) shielding have attracted increasing interest because of rapid development of smart communication devices. To meet the requirement in portable electronic devices, flexible shielding materials with ultrathin characteristic have been pursued for this purpose. In this work, we demonstrated a facile strategy for scalable fabrication of flexible all-carbon networks, where the insulting polymeric frames and interfaces have been well eliminated. Microscopically, a novel carbon nanofiber-graphene nanosheet-carbon nanofiber (CNF-GN-CNF) heterojunction, which plays the dominant role as the interfacial modifier, has been observed in the as-fabricated networks. With the presence of CNF-GN-CNF heterojunctions, the all-carbon networks exhibit much increased electrical properties, resulting in the great enhancement of EMI shielding performance. The related mechanism for engineering the CNF interfaces based on the CNF-GN-CNF heterojunctions has been discussed. Implication of the results suggests that the lightweight all-carbon networks, whose thickness and density are much smaller than other graphene/polymer composites, present more promising potential as thin shielding materials in flexible portable electronics.

Hollow Core–Shell SnO2/C Fibers as Highly Stable Anodes for Lithium-Ion Batteries

Given their competitive prospects for energy storage, lithium-ion batteries (LIBs) have attracted ever-intensive research interest. However, the large volume changes during cycling and structural pulverization significantly hinder the cycling stability and high capacity for lithium-alloy electrodes. Herein, novel one-dimensional (1D) hollow core-shell SnO2/C fibers were synthesized by facile coaxial electrospinning. The as-prepared fibers that possess sufficient hollow voids and nanosized SnO2 particles on the inner shell are able to serve as an anode in LIBs. The results suggest a reversible capacity of 1002 mAh g(-1) (for the initial cycle at 100 mA g(-1)), excellent rate capability, and a highly stable cycling performance with a discharge capacity of 833 mAh g(-1) after 500 cycles at 600 mA g(-1). The superior electrochemical performance is attributed to the unique hollow core-shell structure, which offers sufficient voids for alleviating the volume changes of SnO2 nanoparticles during lithiation/delithiation processes. The promising strategies and associated opportunities here demonstrate great potential in the fabrication of advanced anode materials for long-life LIBs.

Improved dielectric properties and highly efficient and broadened bandwidth electromagnetic attenuation of thickness-decreased carbon nanosheet/wax composites

Carbon-based composites with various potential applications based on their unique properties are highly attractive. Lightweight electromagnetic attenuation composites embedded with carbon materials, specifically carbon nanosheets or graphene, are considered to offer promising attenuation performance due to their excellent electrical properties. Generally, graphene and carbon nanosheets are mostly achieved via chemical oxidation and subsequent reduction of commercial graphite, and the recovery of the electrical properties for the resulting products substantially depends on the reducing approaches. In this work, a direct chemical exfoliation approach has been applied to fabricate carbon nanosheets without sacrificing electrical properties. Thickness effects of the carbon nanosheets on the percolation threshold were investigated in the ethylene-vinyl acetate-based composites. These polymeric composites filled with thickness-decreased carbon nanosheets were found to exhibit much lower percolation threshold compared to those filled with unexfoliated ones. Thickness-dependent dielectric properties and electromagnetic attenuation were investigated via a direct comparison between unexfoliated and thickness-decreased carbon nanosheets along with corresponding paraffin wax-based composites. The enhanced complex permittivity and efficient electromagnetic attenuation coupled with broadened attenuation bandwidth were observed in the wax-based composites filled with thickness-decreased carbon nanosheets, and the related mechanism was discussed.

Magnetic and conductive graphene papers toward thin layers of effective electromagnetic shielding

Graphene-based hybrids, specifically free-standing graphene-based hybrid papers, have recently attracted increasing attention in many communities for their great potential applications. As the most commonly used precursors for the preparation of graphene-based hybrids, electrically-insulating graphene oxides (GO) generally must be further chemically reduced or thermally annealed back to reduced GO (RGO) if high electrical conductivity is needed. However, various concerns are generated if the hybrid structures are sensitive to the treatments used to produce RGO. In this work, we develop a highly facile strategy to fabricate free-standing magnetic and conductive graphene-based hybrid papers. Electrically conductive graphene nanosheets (GNs) are used directly to grow Fe3O4 magnetic nanoparticles without additional chemical reduction or thermal annealing, thus completely avoiding the concerns in the utilisation of GO. The free-standing Fe3O4/GN papers are magnetic, electrically conductive and present sufficient magnetic shielding (>20 dB), making them promising for applications in the conductive magnetically-controlled switches. The shielding results suggest that the Fe3O4/GN papers of very small thickness (<0.3 mm) and light weight (∼0.78 g cm−3) exhibit comparable shielding effectiveness to polymeric graphene-based composites of much larger thickness. Fundamental mechanisms for shielding performance and associated opportunities are discussed.