Yongjun Chen

Water-assisted chemical vapor deposition synthesis of boron nitride nanotubes and their photoluminescence property.

A novel water-assisted chemical vapor deposition (CVD) method for the efficient synthesis of boron nitride (BN) nanotubes is demonstrated. The replacement of metal oxide by water vapor could continuously generate intermediate boron oxide vapor and enhance the production of BN nanotubes. The nanotubes synthesized when an appropriate amount of water vapor was introduced had an average diameter of about 80 nm and lengths of several hundred μm. The diameter and yield of nanotubes could be controlled by tuning the amount of water vapor. This simple water-assisted CVD approach paves a new path to the fabrication of BN nanotubes in large quantities.

Preparation of boron nitride nanosheet-coated carbon fibres and their enhanced antioxidant and microwave-absorbing properties

In this study, annealing carbon fibres with boron and FeCl3·6H2O at elevated temperatures was demonstrated as a novel route to coat carbon fibres with boron nitride (BN) nanosheets. The effect of annealing temperature on the thickness and microstructure of BN coating was investigated. Results showed that BN coating hardly formed at 1000 °C, and uniform BN coating was achieved at 1100 °C and 1200 °C. However, further increasing the temperature to 1250 °C triggered the formation of discretely distributed BN particles on the surface of the BN coating in addition to the formation of a uniform BN coating. The BN coating and particles were constructed by numerous BN nanosheets with a bending and crumpling morphology. The thickness of the BN coating increased with increasing annealing temperature. The oxidation resistance of the carbon fibres dramatically enhanced after BN nanosheets were coated onto the carbon fibre surface. Moreover, given the low dielectric loss tangent of BN, the BN coating can improve the impedance matching of carbon fibres and enhance the microwave-absorbing property of carbon fibres significantly.

Ti2Nb2xO4+5x anode materials for lithium-ion batteries: a comprehensive review

Lithium-ion batteries (LIBs) have achieved great success in portable electronics, but their applications in electric vehicles (EVs) are still very challenging owing to the lack of high-performance electrode materials with high specific capacities, safety, rate capability and cycling stability. Recently, intercalating Ti2Nb2xO4+5x anode materials have received intensive attention owing to their high specific capacities (388–402 mA h g−1), high safety, prolonged cycling stability, easy state-of-charge evaluation and significant pseudocapacitive behavior. Their limited rate capabilities can be significantly improved by various modifications, including crystal structure modification, formation of a composite conductive phase, particle size reduction, and combined methods. These modified Ti2Nb2xO4+5x materials can be promising and practical anode materials for LIBs in EVs. Here, the research history, crystal structures, characteristics, working mechanisms and various modifications of Ti2Nb2xO4+5x are comprehensively reviewed. The relations between the material composition, material fabrication, material structure, material properties and LIB performance are emphasized. An insight into future directions in this research community is also provided.

Advanced composites of complex Ti-based oxides as anode materials for lithium-ion batteries

AbstractLithium-ion batteries (LIBs) are increasingly used in portable electronics due to their high energy densities, long cycle life, low self-discharge properties, and environmentally friendly features. To satisfy future large-scale energy storage, the development of high-performance electrode materials is highly important. Complex Ti-based oxides (such as Li4Ti5O12 and Li–M–Ti–O) have interesting properties for anode applications, including good safety performance and high cyclic stability. However, most of the complex Ti-based oxides suffer from low electronic conductivities and insufficient Li+-ion diffusion coefficients, significantly limiting their rate capabilities. In general, compositing is an effective strategy to tackle this issue. Comprehensively good electrochemical performance can be achieved in the composites arising from the complementarity and correlation of the components. This review focuses on the composite characteristics and compositing methods of the complex Ti-based oxides for high-performance lithium-ion storage. The relations among the material composition, material fabrication, material structure, material property and LIB performance are emphasized. In addition, a vista of future research and development in this research field is also presented.n Graphical abstractThis review focuses on the composite characteristics and compositing methods of the complex Ti-based oxides for high-performance lithium-ion storage.

Mg2Nb34O87 Porous Microspheres for Use in High-Energy, Safe, Fast-Charging, and Stable Lithium-Ion Batteries

M-Nb-O compounds are advanced anode materials for lithium-ion batteries (LIBs) due to their high specific capacities, safe operating potentials, and high cycling stability. Nevertheless, the found M-Nb-O anode materials are very limited. Here, Mg2Nb34O87 is developed as a new M-Nb-O material. Mg2Nb34O87 porous microspheres (Mg2Nb34O87-P) with primary-particle sizes of 30-100 nm are fabricated based on a solvothermal method. Mg2Nb34O87 has an open 3 × 4 × ∞ Wadsley-Roth shear structure and a large unit-cell volume, leading to its largest Li+ diffusion coefficients among all the developed M-Nb-O anode materials. In situ X-ray diffraction analyses reveal its high structural stability and intercalating characteristic. These architectural, conductivity, and structural advantages in Mg2Nb34O87-P lead to its most significant intercalation pseudocapacitive contribution (87.7% at 1.1 mV s-1) among the existing M-Nb-O anode materials and prominent rate capability (high reversible capacities of 338 mAh g-1 at 0.1C and 230 mAh g-1 at 10C). Additionally, this new material exhibits a safe operating potential (∼1.68 V), an ultrahigh initial Coulombic efficiency (94.8%), and an outstanding cycling stability (only 6.9% capacity loss at 10C over 500 cycles). All of these evidences indicate that Mg2Nb34O87-P is an ideal anode material for high-energy, safe, fast-charging, and stable LIBs.