Mn-Based compounds with high reversible capacities and eco-friendliness are one of the most promising anode materials for lithium ion batteries (LIBs), but their practical applications are still hindered by low rate capability, poor cycling stability, and high cost of production. Herein, we synthesize MnCO3/Mn3O4/reduced graphene oxide (MnCO3/Mn3O4/RGO) ternary composites through a green and facile strategy, which can take full advantage of the raw materials, mitigate pollution effectively, simplify the operating procedure, and shorten the preparation time to realize large-scale preparation. When used as anode materials for LIBs, benefitting from the advantage of their structure and effective synergy among MnCO3, Mn3O4 and graphene, the ternary composites exhibit an excellent cycling stability of 988 mA h g−1 after 200 cycles at 100 mA g−1 and 532 mA h g−1 after 800 cycles at 1 A g−1, which is superior to those of binary MnCO3/RGO and Mn3O4/RGO composites. Analyses using cyclic voltammetry, charge/discharge profiles, and electrochemical impedance spectroscopy reveal improved kinetics in the electrochemical reaction of the MnCO3/Mn3O4/RGO ternary composite with cycling. Furthermore, a systematic study of the potential difference of the redox reaction provides a good explanation for the observed electrochemical performance of the ternary composites.

Mn-Based compounds with high reversible capacities and eco-friendliness are one of the most promising anode materials for lithium ion batteries (LIBs), but their practical applications are still hindered by low rate capability, poor cycling stability, and high cost of production. Herein, we synthesize MnCO3/Mn3O4/reduced graphene oxide (MnCO3/Mn3O4/RGO) ternary composites through a green and facile strategy, which can take full advantage of the raw materials, mitigate pollution effectively, simplify the operating procedure, and shorten the preparation time to realize large-scale preparation. When used as anode materials for LIBs, benefitting from the advantage of their structure and effective synergy among MnCO3, Mn3O4 and graphene, the ternary composites exhibit an excellent cycling stability of 988 mA h g−1 after 200 cycles at 100 mA g−1 and 532 mA h g−1 after 800 cycles at 1 A g−1, which is superior to those of binary MnCO3/RGO and Mn3O4/RGO composites. Analyses using cyclic voltammetry, charge/discharge profiles, and electrochemical impedance spectroscopy reveal improved kinetics in the electrochemical reaction of the MnCO3/Mn3O4/RGO ternary composite with cycling. Furthermore, a systematic study of the potential difference of the redox reaction provides a good explanation for the observed electrochemical performance of the ternary composites.

•Both carbon and graphene are N-doped with melamine formaldehyde resin.•Combined effect of N-doped graphene and CNTs as conductive matrices in Si-rGO/NCT.•The composite exhibits good rate and cycling performance.A Si-rGO/NCT composite, in which Si nanoparticles (SiNPs) are enwrapped with N-doped carbon and combine with N-doped graphene and CNTs as conductive matrices synthesized by simple solution-mixing and carbonization process with pyrolyzing melamine formaldehyde resin (MFR) is developed as a promising candidate anode material for lithium ion batteries (LIBs). The N-doped carbon outside SiNPs can not only improve the electrical conductivity of the composite, but also buffer the stress causing by huge volume change of SiNPs during the lithiation/delithiation process. The Si-rGO/NCT composite exhibits high specific capacity and good cycling stability (892.3 mAh g−1 at 100 mA g−1 up to 100 cycles), as well as improved rate capability. This approach provides a very facile route to obtain silicon-based anode materials.

•The rGO/SnO2-C composites were designed and synthesized at a low cost.•The flexible anode was prepared without any additives.•Amorphous carbon covering on the SnO2 nanoparticles leads to the high capacity retention and coulombic efficient.The three-dimensional carbonized cotton framework covered by reduced graphene oxide (rGO) was uniformly decorated by the SnO2 nanoparticles encapsulated by a layer of the amorphous carbon and was directly used in the anode materials for the lithium ion battery. The carbonized frameworks covered by rGO are interconnected and the pores are enriched, facilitating the diffusion of electron and releasing the strain of lithium ions insertion and extraction. The rGO sheets with better mechanical and foldable characterization increase the conductive and buffer the electrode expansion during the cycling process. Furthermore, the amorphous carbon coating effectively prevents the direct contact between the SnO2 nanoparticles and the electrolyte, which can format a stable solid electrolyte interphase and greatly reduce the irreversible reaction. As a result, the capacity of composite is as high as 496.3 mAh g− 1 (1.72 mAh cm− 2) after 200 cycles at current density of 100 mA g− 1, which means that the product as free-standing and binder-free electrode exhibits the stable cycle performance and will be a promising material for the application of lithium ion battery.Download high-res image (116KB)Download full-size image

•Hexagonal/turbostratic composite boron nitride nanosheets (h/t-BNNSs) are fabricated by a facile chemical foaming process.•The h/t-BNNSs possess a large lateral size of tens of micrometers with thickness of tens of nanometers.•These h/t-BNNSs can be used to effectively improve the thermal conductivity of polymers.In this report, we have developed a scalable approach to massive synthesis of hexagonal/turbostratic composite boron nitride nanosheets (h/t-BNNSs). The strikingly effective, reliable, and high-throughput (grams) synthesis is performed via a facile chemical foaming process at 1400 °C utilizing ammonia borane (AB) as precursor. The characterization results demonstrate that high quality of h/t-BNNSs with lateral size of tens of micrometers and thickness of tens of nanometers are obtained. The growth mechanism of h/t-BNNSs is also discussed based on the thermogravimetric analysis of AB which clearly shows two step weight loss. The h/t-BNNSs are further used for making thermoconductive h/t-BNNSs/epoxy resin composites. The thermal conductivity of the composites is obviously improved due to the introduction of h/t-BNNSs. Consideration of the unique properties of boron nitride, these novel h/t-BNNSs are envisaged to be very valuable for future high performance polymer based material fabrication.Download high-res image (164KB)Download full-size image

ABSTRACTFlexible freestanding cotton–graphene (CGN) composites were prepared by a simple immersion and freeze-drying method and a thermal annealing process together. The composites had a constant cotton microstructure covered by graphene. The microstructure and morphology of the composites could be easily adjusted through the variation of the thermal annealing temperatures. Electrochemical tests demonstrated that the annealing temperatures had great effects on the electrochemical performances of the obtained composites. The CGN composite annealed at 700 °C exhibited a reversible capacity of 245.2 mAh/g after 100 cycles. Even after it was bent 1000 times, the CGN composite still maintained its superior electrochemical properties. The results suggest that because of its high flexibility and excellent conductive and electrochemical activities, the CGN composites could be used as lithium-ion battery anode materials on a large scale for corresponding applications. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44727.

•The 3D macroscopic graphene hydrogels (MGHs) were synthesized by hydrothermal method.•Combined effect of nitrogen- and oxygen-containing functional Groups in MGHs.•The MGHs exhibits good rate capability and cycling stability.In this work, the 3D macroscopic graphene hydrogels (MGHs) with a high capacitor performance were easily prepared by a one-step hydrothermal method from graphene oxide (GO) dispersions. A very small amount of 1,4-butanediamine was employed to realize the partial reduction of GO, modification of the 3D structure of MGHs, and nitrogen doping of graphene, at the same time. The synthesized MGH-6 sample in the wet state exhibit a high specific capacitance of 268.8 Fg−1 at 0.3 A g−1 in 6 M KOH electrolyte, and this capacitance can be maintained for 84.9% even as the discharging current density was increased up to 10 A g−1. The MGH-6 sample also shows good cycle stability along with a 1.03% increase of its initial specific capacitance after 10000 cycles at current density of 10 Ag−1. These remarkable properties are ascribed to the both nitrogen- and oxygen-containing functional groups, modified macroporous 3D framework, and the high specific surface area of the graphene. Combining with the economical and easy path toward mass production, the present MGH-6 can be expected as a promising candidate for high-performance supercapacitors.

The thermal management of smart and wearable electronics has become a serious issue, due to their reducing size and increasing power density, which has high requirement on weight, size and thermal conductance. In this paper, we propose an effective approach to fabricate Cu–graphite–Cu (Cu–G–Cu) sandwich heat spreaders by electroplating Cu on synthetic graphite sheets. The binding between Cu layers and graphite-syn sheets was largely improved by the fastening of microholes. We demonstrate experimentally that the obtained Cu–G–Cu heat spreaders with higher thermal conductance (526–626 W (m K)−1) and thermal diffusivity (319–442 mm2 s−1) and lower density (2.36–3.17 g cm−3) present outstanding ability of heat dissipation on electronic cooling as compared with Cu substrates. The temperature of a chip attached to a 35 μm Cu–G–Cu sandwich was ∼8 °C lower than that on 50 μm Cu foil with the chip power of 1.4 W. Moreover, Ansys simulation illustrates that the temperature of the chip attached to the Cu–G–Cu sandwich with Sn solder as the thermal interface material (TIM) can be further reduced by 22.06 ± 9.88 °C (3.0 W) compared with that with polymer adhesive as a TIM, due to its good weldability with Sn solder and lower contact thermal resistance, revealing the huge benefits of the obtained Cu–G–Cu sandwich heat spreaders.

The free-standing and binder-free electrode materials, cotton/graphene (CGN) composites were prepared via a simple “dipping and freeze-drying” process using raw cotton as the supporting body (platform) and graphene oxide (GO) as the suspension. Then the cotton/GO (CGO) composites were annealed at 1000 °C under an Ar flow conditions to obtain CGN composites. The results show that the CGN structure can protect the cotton framework and have better thermal stable property than the cotton alone. Galvanostatic charge–discharge tests demonstrated that the GO concentration had great effects on their electrochemical performances. The CGN (for the GO with 3 and 5 mg ml−1) provide reversible discharge capacity of 160 mAh g−1 after 100 cycles, which is about 1.5 times higher than that of the cotton alone (115 mAh g−1 after 100 cycles). Excellent electrochemical properties of CGN can be ascribed to its controllable structure with more lithium ion storage sites, high electronic conductivity, and fast ion diffusion velocity. The results suggest that this work develops a simple, cheap, and suitable large-scale production method in the lithium-ion batteries.

•1,4-dioxane is proved to be a good pretreatment liquid for lithium electrode.•The surface modification mechanisms are studied by FTIR, SEM and EIS methods.•A reasonable equivalent circuit is designed for EIS analysis.•The equivalent circuit model is analyzed theoretically.Lithium metal electrode is pretreated with 1,3-dioxolane or 1,4-dioxane to improve its properties. The components and morphology of the surface films formed in the above two pretreatment liquids are studied using FTIR and SEM respectively. Li–LiCoO2 coin cells are then fabricated and their cycle and discharge performance are tested. It is found that the battery performance is greatly improved by such pretreatment. Interestingly, the 1,4-dioxane pretreatment is more effective than 1,3-dioxolane in improving the lithium metal electrode performance. To explore the mechanism(s) behind, the electrochemical impedance spectroscopy (EIS) is employed and an equivalent circuit model is designed for EIS analysis. The fitting curves are aligned well with the experimental curves, suggesting that the proposed equivalent circuit model is an ideal model for lithium battery. Next, the corresponding relationship between the impedance components and every individual semicircle in the Nyquist curves is inferred theoretically and the result is satisfying. Based on the analysis using this model, we conclude that the structural stability of SEI film is increased and the interfacial compatibility between the lithium substrate and the SEI film is improved by 1,3-dioxolane or 1,4-dioxane pretreatment.

Zirconia-toughened alumina (ZTA)/boron nitride (BN) machinable ceramics have been successfully fabricated by reactive hot pressing. BN was in-situ introduced into the composite by the reaction of aluminum nitride (AlN) and boric acid (H3BO3). The microstructure of ZTA/BN composite was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. The results indicated that BN grains were uniformly and compactly distributed among Al2O3 and ZrO2 grains. The relative density, flexural strength, fracture toughness, and Vickers hardness increased with increasing temperature. The flexural strength and fracture toughness of the ZTA/BN composite with BN content of 12.5 vol% sintered at 1800 °C achieved high values of 731 MPa and 7.48 MPa m1/2, respectively. These values were much higher than those of the composite with the same composition prepared by conventional powder sintering method, and even higher than those of the monolithic ZTA ceramics. The enhancements of the fracture strength and fracture toughness were primarily ascribed to the reactive hot pressing method which introduced BN in-situ and prevented the aggregation of BN and reduced the flaw sizes. The ZTA/BN composite exhibited excellent machinability and could be drilled using conventional cemented carbide drill bits.

•Novel turbostratic BN thin films have been fabricated on SiO2/Si substrates by a facile chemical vapor deposition method.•The thin film exhibited a novel turbostratic graphite-like structure.•The micro-Raman spectrum of the thin film was found unexpectedly broadened and blue-shifted relative to that of the bulk hexagonal BN.Novel turbostratic BN thin films have been fabricated via a facile chemical vapor deposition route on SiO2/Si substrates. The BN thin film grew continuously on the entire SiO2/Si surface and the region with uniform thickness (~150 nm) can be up to several centimeters in lateral size which is only limited by the size of the substrate. The thin film exhibited a novel turbostratic graphite-like structure. Moreover, the micro-Raman spectrum of the thin film was found unexpectedly broadened and blue-shifted relative to that of the bulk hexagonal BN. The reason for the peculiar Raman scattering behavior of the turbostratic BN thin films was briefly discussed.

Two types of homogeneous NiCo2O4 nanosheet@NiCo2O4 nanorod and heterogeneous NiCo2O4 nanosheet@NiO nanoflake hierarchical core–shell arrays are synthesized via facile solution methods in combination with a simple thermal treatment. In both cases, the NiCo2O4 nanosheets serve as the core backbone for anchoring the shell materials. The two as-prepared hierarchical nanoarrays are evaluated as supercapacitor electrodes and demonstrate excellent electrochemical performance with high specific capacitance (1925 and 2210 F g−1 for NiCo2O4@NiCo2O4 and NiCo2O4@NiO at 0.5 A g−1, respectively), good rate capability, and superior cycling stability. The superior capacitive performance is mainly due to the unique hierarchical core–shell architecture with faster ion/electron transfer, improved reactivity, and enhanced structural stability. Our work can allow for the fabrication of various NiCo2O4 nanosheet supported hierarchical nanostructures for applications in energy storage, catalysis, and sensing.

High purity microporous B–C–N ceramics have been successfully synthesized by precursor spraying route without the assistance of template and any other additives. Scanning electron microscopy (SEM) investigation indicated that the sizes of the pores in the ceramics were ranging from 5 to 20 μm. Nitrogen adsorption measurements showed that the products had a surface area of 55 m2 g−1. X-ray photoelectron spectrometer (XPS) and TEM revealed that the main compositions of the products were graphite and hexagonal B–C–N ternary compound.Graphical abstractHighlights► B–C–N porous architectures with a pore size ranging from 5–20 μm in diameters have been prepared. ► No oxygen, catalysts and other impurities are involved in synthetic processes. ► Demonstrated way to synthesize homogenous B–C–N micropores with a surface area of 55 m2 g−1.

Novel one-dimensional heterostructures composed of single crystalline cubic SiC cores, intermediate amorphous SiO2 layers, and single crystalline hexagonal BN (h-BN) sheaths (i.e. SiC–SiO2–BN nanocable) have been successfully fabricated in large scale using SiC–SiO2 nanocables and ammonia borane as starting materials. The structure and chemical composition of the as-synthesized products are determined by powder X-ray diffraction, field emission scanning electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and energy filtered TEM based on electron energy loss spectroscopy. The nanocables are approximately 100 nm in diameter and up to 1 millimetre in length. The intermediate amorphous SiO2 layers and the outer h-BN sheaths are about 10 nm and 5 nm thick, respectively. Interestingly, an increase in the amount of ammonia borane leads to the transformation of SiC–SiO2 nanocables into BN nanotubes. Mass spectrometric analysis shows that the vapors decomposed from ammonia borane play crucial roles both in the growth of the BN sheath on the SiC–SiO2 nanocables and in the transformation to the BN nanotubes. The SiC–SiO2–BN nanocable displays similar photoluminescence (PL) characteristics with respect to the original SiC–SiO2 nanocable but with the 488.5-nm emission peak blue shifting. The synthetic route has also been extended to fabricate SiC–BN nanocables and has proved effective and universal for the synthesis of core–sheath nanostructures with BN sheaths.

Hollow microspheres constructed by single-crystalline hexagonal boron nitride (h-BN) nanoplates have been synthesized via a facile chemical vapour reaction route employing ammonia borane as a starting material. The as-synthesized products are extensively characterized by field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), selected-area electron diffraction (SAED), and electron energy loss spectroscopy (EELS). The hollow microspheres are in nest-like morphology with diameters of ∼3 μm and are composed of numerous single-crystalline h-BN nanoplates of 200–500 nm in diameter and 10–30 nm in thickness. The dependence of the morphology of the BN hollow microspheres on experimental parameters, such as reaction temperature, holding time and gas pressure, is systematically investigated. The reaction temperature and holding time are proved to be key parameters to tailor the morphology of the final products. Controlled experiments indicate that the growth process of the BN hollow microspheres involves the formation of smooth bowl-shaped hollow microspheres and their subsequent growth into the hierarchical ones. The BN hollow microspheres exhibit intense cathodoluminescence emissions in the region of 200 to 400 nm, indicating that they could be potentially used as compact ultraviolet (UV) laser emitters.

A new kind of boron nitride (BN) whisker with a novel cap-stacked structure and excellent ultraviolet−visible luminescence properties has been successfully prepared via a facile chemical vapor reaction route. SEM analysis shows that the BN whiskers are uniform with a mean diameter of 1 μm and a length up to at least 1 mm. TEM images and the electron diffraction patterns indicate that the BN whiskers are constructed by stacking numerous cap-shaped BN sheets along the axial direction. The BN sheets are almost perpendicular to the whisker axis. The chemical compositions and the bonding characteristics of the BN whiskers are confirmed by EELS, XPS, and FTIR results. The diameters of the BN whiskers could be controlled by tuning the reaction pressure and temperature. The growth mechanism and morphology evolution of the BN whiskers are explained on the basis of the vapor−liquid−solid mechanism. Both photoluminescence and cathodoluminescence spectra of the BN whiskers exhibit broad emission bands from 200 to 700 nm, indicating that they could be used as compact light emitters at both ultraviolet and visible wavelengths.

SiBONC ceramic powders have been prepared via a polymer pyrolysis route using silicon tetrachloride (SiCl4), benzaldehyde (PhCHO), boron trichloride (BCl3) and aniline (PhNH2) as starting materials. Fourier transform infrared spectra (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and transmission electron microscopy (TEM) were performed to investigate the structural characteristics of the polymer precursor and the ceramic powders. The SiBONC ceramic powders in spherical shape with a mean diameter of 50 nm are amorphous and composed of B–N, Si–O, Si–C, and SiONx groups. The SiBONC ceramic powders were sintered at 1700 °C to a dense material which still remained amorphous.

Silicon carbide nanowires (NWs), that were over 200 μm in length and 20–200 nm in diameter, were prepared by high-pressure reaction from SiBONC powder tablets. Annealing temperatures between 1,500 °C and 1,600 °C and Si/B molar ratios between 70:30 and 60:40 were suitable for the growth of the nanowires. The nanowires were fabricated by in situ chemical vapor growth process on the tablets. The SiC nanowires were identified as single crystal β-SiC. The analysis of X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed the single crystalline nature of nanowires with a growth direction of <111>. Massive growth of single crystalline SiC nanowires is important to meet the requirements of the fabrication of SiC nanowire-based nanodevices.

The C–W2B5 composite was fabricated by reaction hot-pressing of B4C and WC powders. The effect of applied load on the friction and wear behavior was investigated by the block-on-ring test in air. In particular, the composition and microstructural characterization of the mechanically mixed layers (MML) and wear debris formed during sliding wear were studied using scanning electron microscopy (SEM) with EDX and X-ray diffraction (XRD). The results revealed that the friction coefficients and wear rates of the composite increased with increasing testing load. The MML and wear debris generated from the sliding system had similar microstructural features and were composed of a mixture of ultrafine grained structures which mainly consisted of W2B5, Fe and Fe2O3. The formation mechanism of the MML and their influences on wear mechanism of the multiphase material were also studied on the basis of the microstructural observations.

Highly densified W2B5/C composites with W2B5 content from 30 to 70 vol% were fabricated by reaction hot pressing of the powder mixture of B4C, WC and carbon black. The reaction products were identified by XRD analysis to consist of only W2B5 and carbon, regardless of carbon content. The reaction formed composites have excellent mechanical properties (the maximum flexural strength and fracture toughness of 786 MPa and 8.9 MPa m1/2 respectively), electrical conductivity (the highest electrical conductivity of 1.64 × 106 Ω−1 m−1), and resistance to both wear and oxidation because of the presence of the plate-like W2B5 grains. In this paper, the preparation, microstructure and properties of this new composite are investigated, and the strengthening, toughening, conduction mechanisms are discussed.

Two types of homogeneous NiCo2O4 nanosheet@NiCo2O4 nanorod and heterogeneous NiCo2O4 nanosheet@NiO nanoflake hierarchical core–shell arrays are synthesized via facile solution methods in combination with a simple thermal treatment. In both cases, the NiCo2O4 nanosheets serve as the core backbone for anchoring the shell materials. The two as-prepared hierarchical nanoarrays are evaluated as supercapacitor electrodes and demonstrate excellent electrochemical performance with high specific capacitance (1925 and 2210 F g−1 for NiCo2O4@NiCo2O4 and NiCo2O4@NiO at 0.5 A g−1, respectively), good rate capability, and superior cycling stability. The superior capacitive performance is mainly due to the unique hierarchical core–shell architecture with faster ion/electron transfer, improved reactivity, and enhanced structural stability. Our work can allow for the fabrication of various NiCo2O4 nanosheet supported hierarchical nanostructures for applications in energy storage, catalysis, and sensing.

Novel one-dimensional heterostructures composed of single crystalline cubic SiC cores, intermediate amorphous SiO2 layers, and single crystalline hexagonal BN (h-BN) sheaths (i.e. SiC–SiO2–BN nanocable) have been successfully fabricated in large scale using SiC–SiO2 nanocables and ammonia borane as starting materials. The structure and chemical composition of the as-synthesized products are determined by powder X-ray diffraction, field emission scanning electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and energy filtered TEM based on electron energy loss spectroscopy. The nanocables are approximately 100 nm in diameter and up to 1 millimetre in length. The intermediate amorphous SiO2 layers and the outer h-BN sheaths are about 10 nm and 5 nm thick, respectively. Interestingly, an increase in the amount of ammonia borane leads to the transformation of SiC–SiO2 nanocables into BN nanotubes. Mass spectrometric analysis shows that the vapors decomposed from ammonia borane play crucial roles both in the growth of the BN sheath on the SiC–SiO2 nanocables and in the transformation to the BN nanotubes. The SiC–SiO2–BN nanocable displays similar photoluminescence (PL) characteristics with respect to the original SiC–SiO2 nanocable but with the 488.5-nm emission peak blue shifting. The synthetic route has also been extended to fabricate SiC–BN nanocables and has proved effective and universal for the synthesis of core–sheath nanostructures with BN sheaths.