Tempura-like carbon/carbon composite as advanced anode materials for K-ion batteries

Graphite as a promising anode candidate of K-ion batteries (KIBs) has been increasingly studied currently,but corresponding rate performance and cycling stabili...     

Directly conversion the biomass-waste to Si/C composite anode materials for advanced lithium ion batteries

The necessity to explore high-efficiency and high-value utilization strategy for biomass-waste is desirable.Herein,the strategy for direct conversion biomass-waste(rice husks) to Si/C composite structure anode was built.The Si/C composite materials were successfully obtained via the typical thermal reduction with magnesium,and the Si nanopa rticle was uniformly embedded in carbon frame,as revealed by Raman,X-ray diffraction(XRD) and transmission electron microscope(TEM) measurement.The carbon structure among rice husks was effectively used as a protective layer to accommodate the volume variation of Si anode during the repeated lithiation/delithiation process.Benefitting from the structure design,the batteries show a superior electrochemical stability with the capacity retention rate above 90% after 150 cycles at the charge/discha rge rate of 0.5 C(1 C=600 mAh/g),and hold a high charge capacity of 420.7 mAh/g at the rate of 3 C.Therefore,our finding not only provides a promising design strategy for directly conversion biomass-waste to electrochemical storage materials but broadens the high-efficiency utilization method for other biomass by-products.     

Morphology of a phase-separated and a molecular composite PBT/ABPBI polymer blend

The structure and morphology of homopolymers and blends of rigid-rod poly(p-phenylene benzobisthiazole) (PBT) and semiflexible coil poly[2,5(6)benzimidazole] (ABPBI) were examined by wide-angle x-ray diffraction and scanning and transmission electron microscopy. When samples were processed from a solution where the total polymer concentration of 30% PBT/70% ABPBI blend was greater than a critical concentration, large-scale phase separation occurred and 0.1–4 μm ellipsoidal particles were present in a ductile matrix. The ellipsoids were chiefly composed of aggregates of well-oriented 10-nm PBT crystallites, while the matrix material was chiefly ABPBI. When the concentration was less than a critical concentration, the solution was optically homogeneous. In processing of fiber and film samples from the homogeneous solution, large-scale phase separation was inhibited by rapid coagulation in a water bath. After heat treatment, these samples were found to contain crystallites of both PBT and ABPBI with lateral dimensions of ordered regions no larger than 3 nm. The PBT homopolymer was dispersed in the matrix at the molecular level in ordered regions at a scale no larger than 3 nm, resulting in a rigid-rod molecular composite. In the rigid-rod molecular composite fiber both the molecular-level dispersion and high orientation contributed to higher values of strength and modulus compared to the properties of a phase-separated fiber. The strength and modulus of highly oriented fiber were only 25% higher than those of planar isotropically oriented film, suggesting that the level of dispersion of rod molecules is more important than orientation of the reinforcing phase in rigid-rod molecular composites.     

Thermal behaviour of advanced composite materials based on SiC fibres

Emanation thermal analysis (ETA) was used for characterization of thermal behaviour of SiC_f/SiC composites on heating in argon and air, respectively. Effect of gas environment (argon, air) and helium ions implantation on the microstructure development of the SiC_f/SiC composite prepared by chemical vapour infiltration (CVI) from Nicalon CG fibres was investigated under in situ conditions of heating. The annealing of near surface structure irregularities was observed in the range 280-700°C and evaluated by means of the mathematical model, assuming that the structure irregularities served as diffusion paths for radon. The ETA reflected the formation of amorphous silica and its subsequent crystallization to crystoballite. Morphology of the SiC_f/SiC samples before and after the heat treatments was characterized by means of SEM. This revised version was published online in July 2006 with corrections to the Cover Date.     

Fabrication of polymer/fluoride-containing salts blend composite membranes for CO_2 separation

Poly (N,N-dimethylaminoethyl methacrylate)-poly (ethylene glycol methyl ether methacrylate) (PDMAEMA-PEGMEMA) and cesium fluoride (CsF) were blended and used as the separation material of composite membranes.Hollow fiber composite membranes were fabricated by coating the blend on polysulfone (PSf) hollow fiber substrate.Introduction of fluorine ion improved the separation performance of the membrane.The concentration of coating solution was adjusted to obtain a membrane with high permeance.The composite membrane showed good performance with the CO2 permeance of 30.4 GPU (1 GPU=10-6 cm3 (STP)/(cm 2 s cmHg)),and selectivities to CO2/N2,CO2/CH4,CO2/H2 and O2/N2 of 47.2,37.6,1.75 and 4.70,respectively.Potassium fluoride (KF),due to its low cost,was also used as a substitute of CsF to prepare composite membrane and the permeation data showed that CsF can be replaced by KF.The effect of operating temperature on the permeation properties of the composite membrane was also investigated.     

Fabrication of polymer/fluoride-containing salts blend composite membranes for CO2 separation

Poly (N, N-dimethylaminoethyl methacrylate)-poly (ethylene glycol methyl ether methacrylate) (PDMAEMA-PEGMEMA) and cesium fluoride (CsF) were blended and used as the separation material of composite membranes. Hollow fiber composite membranes were fabricated by coating the blend on polysulfone (PSf) hollow fiber substrate. Introduction of fluorine ion improved the separation performance of the membrane. The concentration of coating solution was adjusted to obtain a membrane with high permeance. The composite membrane showed good performance with the CO2 permeance of 30.4 GPU (1 GPU = 10^-6 cm³(STP)/(cm²·s·cmHg)), and selectivities to CO2/N2, CO2/CH4, CO2/H2 and O2/N2 of 47.2, 37.6, 1.75 and 4.70, respectively. Potassium fluoride (KF), due to its low cost, was also used as a substitute of CsF to prepare composite membrane and the permeation data showed that CsF can be replaced by KF. The effect of operating temperature on the permeation properties of the composite membrane was also investigated.     

Sol-gel preparation and properties of interpenetrating, encapsulating and blend silica-based urea-formaldehyde hybrid composite materials

Four different silica-based urea-formaldehyde (UF/SiO₂) composite materials were prepared by various sol-gel synthetic procedures to yield an interpenetrating (IPN-UF/SiO₂), a micro-size UF resin encapsulated inside silica shell (Encap-UF/SiO₂), a micro-size silica encapsulated inside UF shell (Encap-SiO₂/UF), and a blend mixture (Blend-UF/SiO₂) hybrid systems. The thermal properties of the obtained organic-inorganic hybrid composite materials were examined by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The structure and morphology of the obtained systems were investigated by infrared spectroscopy (FT-IR), powder X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. Their surface porosity and acidity were evaluated from the nitrogen adsorption isotherm and the pH of the corresponding 10% aqueous suspension, respectively. All the results provided evidence for the formation of different hybrid systems with different surface, structural and morphological characteristics.     

Semiconductor nanoparticle/polystyrene latex composite materials

Cadmium sulfide and cadmium selenide/cadmium sulfide core/shell nanoparticles stabilized with poly(cysteine acrylamide) have been bound to polystyrene (PS) latexes by three methods. First, anionic 5 nm diameter CdS particles were electrostatically attached to 130 nm surfactant-free cationic PS latexes to form stable dispersions when the amount of CdS particles was less than 10% of the amount required to form a monolayer on the surface of the PS particles or when the amount of CdS particles exceeded the amount required to form a monolayer on the PS particles. Transmission electron microscopy (TEM) showed nanoparticles on the surface of the latex particles. Fluorescence spectra showed unchanged emission from the nanoparticles. Second, anionic, surfactant-free PS latexes were synthesized in the presence of CdS and CdSe/CdS nanoparticles. TEM showed monodisperse latex particles with trapped nanoparticles. Third, surfactant-stabilized latexes were synthesized by copolymerization of styrene with vinylbenzyl(trimethyl)ammonium chloride electrostatically bound to the CdSe/CdS nanoparticle surface. Brownian motion of the submicroscopic composite particles in water was detected by fluorescence microscopy.     

Designing high-capacity cathode materials for sodium-ion batteries

Na-rich layered oxides as cathode materials for sodium-ion batteries were designed using an electrochemical method based on Li-rich layered oxides. The materials show high specific capacity that can reach 234 mAh/g at a current of 5 mA/g. The energy density of this material (644 Wh/kg) is even higher than those of commercial cathodes for lithium-ion batteries, such as LiFePO₄ and LiMn₂O₄. Kinetic analysis of Na⁺ insertion/extraction into/from the Na-rich layered oxide reveals that the Na⁺ diffusion coefficient is about 10^− 14 cm²/s.     

具有类混凝土结构的 SiOx-C锂离子电池复合材料的制备

采用一种简单的方法制备具有类钢筋混凝土结构的Si-O-C负极材料,其中碳纳米管(carbon nanotubes,CNTs)如同钢筋一般嵌入材料中以提供应力支撑,硅原子被原子级分散的碳和氧原子均匀包裹,最后通过化学气相沉积镀上最外层的碳层,进一步抑制材料的体积变化。基于此独特的结构设计制备的CNTs/SiO_x-C/C负极表现出优异的电化学性能,其在0.5 A·g^-1的电流密度下循环970圈后容量保留率为80%。     

Solid state NMR of a polymer composite and of a polymer blend

Although nuclear magnetic resonance may not seem the technique of choice to study interfaces between components in a polymer composite or polymer blend because of its inherent low sensitivity, for certain systems solid state NMR techniques can emphasize the signals from these interfaces. In case of a composite material with an inorganic filler (particles, fibers) cross-polarization or dipolar dephasing techniques from protons in the organic matrix or in the interphase to nuclei in the filler can be used to selectively observe the nuclei in the surface of the filler. Any changes at the filler surface caused by the presence of the matrix or coupling agent can then be detected. An example of glass reinforced nylon modelcomposites is discussed. The same techniques can also be used to study interphases in polymer blends when one of the components contains a NMR nucleus that is not present in the other component. As an example the blend poly(vinylidene fluoride)-poly(methyl methacrylate) is studied and it is shown that such techniques can provide very detailed information about the miscibility at a molecular scale.     

富勒烯/环糊精复合物及其在生物医药领域的应用

富勒烯有着独特的球形结构,这一结构赋予了其优异的光电及生物性能,在生物医药领域备受关注。环糊精具有良好的水溶性和生物相容性,锥筒状结构赋予了其特异性包合作用,在主客体化学中有着非常重要的地位。富勒烯/环糊精的复合物,结合了富勒烯和环糊精的优势,在DNA切割,光动力学疗法,药物载体等领域发挥了重要作用。本文从富勒烯与环糊精体系的构筑出发,综述了富勒烯/环糊精非共价包合物及共价偶联物在生物医药领域应用的研究进展,且对富勒烯/环糊精复合物的应用进行了展望,为构建新型富勒烯/环糊精复合物提供参考。     

溶剂热法制备MWNTs/CdS复合材料

分别以醋酸镉和硫脲为原料,二乙三胺和去离子水为混合溶剂,采用溶剂热技术制备了MwNTs/CdS复合材料,并用TEM、XRD、FT-IR及UV-vis等技术对材料的结构、形貌和性质进行表征.研究结果表明:硫化镉纳米粒子附着在多壁碳纳米管表面,且无团聚现象.     

Designing composite polymer electrolytes for all-solid-state lithium batteries

Ceramic fast-ion conductors have high ionic conductivities (>10^?4 S cm^?1) but are difficult to process and have poor chemo/mechanical properties at the electrode/electrolyte interfaces. In contrast, polymer electrolytes are pliable and easy to process but suffer from low room-temperature ionic conductivities (≈10^?6-10^?7 S cm^?1). Combining these two elements to form a composite polymer electrolyte is a promising way to enable all-solid-state lithium-metal batteries. The choice of ceramic filler and polymer can be tailored to provide synergistic benefits that overcome the practical shortcomings of the two components. Herein, the fundamentals of Li⁺ conduction through the various phases and interfaces in these materials are discussed as well as the important parameters, beyond the initial choice of polymer and ceramic filler materials that must be considered while designing composite polymer electrolytes. Emphasis is placed on the particle filler engineering and practical fabrication methods as routes toward enhancing the properties of these composites.     

Flame retarding materials for advanced composites

Mechanical properties of advanced composites are often impaired by flame retardants. The least adverse effect is found with synergistic combination of antimony oxides and brominated epoxies. Where low smoke generation is absolutely necessary phenolic resins are used. The new development of combining epoxy and phenolic resin layers in structural applications with high flame retardancy is introduced.     

High capacity silicon/carbon composite anode materials for lithium ion batteries

Silicon/carbon composite materials are prepared by pyrolysis of pitch embedded with graphite and silicon powders. As anode for lithium ion batteries, its initial reversible capacity is 800–900 mAh/g at 0.25 mA/cm² in a voltage range of 0.02/1.5 V vs. Li. The material modification by adding a small amount of CaCO₃ into precursor improves the initial reversibility (η₁=84%) and suppresses the capacity fade upon cycling. A little higher insertion voltage of the composites than commercial CMS anode material improves the cell safety in the high rate charging process.     

邻氨基苯甲酸/SiO2复合材料制备及其光热特性

有机发光体以其较高的发光效率、快速响应能力和较宽的可调谐波长被广泛应用于光转换材料、非线性光学材料和激光材料[1-3]。但是有机物的光学性能不稳定和热稳定性较差,使其在许多方面的应用受到限制。为了提高其光学和热稳定性,常用的方法是将各种有机发光体掺杂在以正硅酸乙酯为原料制得的SiO2凝胶玻璃基质中[4-6]。SiO2凝胶通常采用溶胶 凝胶法通过水解缩合制备。制备时一般采用无机酸作催化剂在酸性条件下进行,对质子酸作用敏感的有机物在酸性条件下往往热稳定性、光学性能下降,甚至遭到破坏。本文以廉价水玻璃为原料,在潜伏酸的…     

Microwave-assisted synthesis of kC/Xylan/PVP-based blend hydrogel materials: physicochemical and rheological studies

Hydrogel systems composed of kC/Xylan (kC/OSX or kC/BX) blends and linear polyvinylpyrrolidone (PVP) were prepared in the presence of water soluble initiator sodium persulphate (KPS) with microwave irradiation. The hydrogel materials were investigated by measuring their syneresis, swelling, gel fraction, and rheological properties. Physicochemical and rheological properties of the natural polysaccharide (kC/Xylans) blends were modified significantly after blending with PVP. The introduction of PVP and the formation of semi-interpenetrating polymer network (semi-IPN) structure improved the gelling properties of the resulting hydrogels. It has been proven, that a high incorporation of PVP could only be obtained if the hydrogels were prepared using KPS initiator and microwave irradiation in combination. FTIR, CP-MAS ¹³C NMR, and elemental analysis confirmed the presence of PVP in the blends but no direct evidence for covalent bonds could be obtained.