Zailei Zhang

Mesoporous CoFe2O4 nanospheres cross-linked by carbon nanotubes as high-performance anodes for lithium-ion batteries

We report the synthesis and characterization of mesoporous cobalt ferrite (CoFe2O4, named CFO) nanospheres cross-linked by carbon nanotubes (CNTs) as anode nanocomposites (CFO/CNT) for Li-ion batteries. CFO/CNT nanocomposites were synthesized by a facile one-pot solvothermal method using Co(CH3COO)2 and FeCl3 as the metal precursors in the presence of CH3COOK, CH3COOC2H5, HOCH2CH2OH, and CNTs. The obtained samples were characterized by X-ray diffraction, thermogravimetric analysis, nitrogen adsorption, transmission electron microscopy, and scanning electron microscopy. It is found that most CFO nanospheres are interconnected with CNTs forming a network composite possibly due to the presence of defects at the open ends and on the external surface of CNTs. These defects may act as nucleation centers for growth of CFO nanospheres. Compared with the bare CFO nanospheres and the physically mixed CFO nanospheres with CNTs, the CFO/CNT composite containing 16.5 wt% CNTs shows much higher capacities of 1137.6, 1003.4, 867.3, and 621.7 mA h g−1 at the current densities of 200, 500, 1000, and 2000 mA g−1 after 10 charge–discharge cycles, respectively, and even after 100 cycles, it still maintains a high capacity of 1045.6 mA h g−1 at 200 mA g−1. The super electrochemical properties of the CFO/CNT composite should originate from the formed network structure with the intimate interconnection between CFO nanospheres and CNTs, which not only provides stable electrical and ionic transfer channels but also significantly shortens the diffusion length of the Li+ ions. This work opens a new way for fabrication and utilization of metal oxide–CNT composites as anode materials for Li-ion batteries.

Facile solvothermal synthesis of mesoporous manganese ferrite (MnFe2O4) microspheres as anode materials for lithium-ion batteries

We report the synthesis and characterization of the mesoporous manganese ferrite (MnFe2O4) microspheres as anode materials for Li-ion batteries. MnFe2O4 microspheres were synthesized by a facile solvothermal method using Mn(CH3COO)2 and FeCl3 as metal precursors in the presence of CH3COOK, CH3COOC2H5, and HOCH2CH2OH. The samples were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, nitrogen adsorption, thermal gravimetric, X-ray photoelectron spectroscopy, temperature programmed reduction, and temperature programmed oxidation. The synthesized mesoporous MnFe2O4 microspheres composed of nanoparticles (10-30 nm) were 100-500 nm in diameter and had surface areas between 60.2 and 86.8 m(2) g(-1), depending on the CH3COOK amounts added in the preparation. After calcined at 600°C, MnFe2O4 was decomposed to Mn2O3 and Fe2O3 mixture. The mesoporous MnFe2O4 microspheres calcined at 400°C showed a capacity of 712.2 mA h g(-1) at 0.2C and 552.2 mA h g(-1) at 0.8C after 50 cycles, and an average capacity fading rate of around 0.28%/cycle and 0.48%/cycle, much better than those of the samples without calcination and calcined at 600°C. The work would be helpful in the fabrication of binary metal oxide anode materials for Li-ion batteries.

Scalable Synthesis of Interconnected Porous Silicon/Carbon Composites by the Rochow Reaction as High‐Performance Anodes of Lithium Ion Batteries

Despite the promising application of porous Si-based anodes in future Li ion batteries, the large-scale synthesis of these materials is still a great challenge. A scalable synthesis of porous Si materials is presented by the Rochow reaction, which is commonly used to produce organosilane monomers for synthesizing organosilane products in chemical industry. Commercial Si microparticles reacted with gas CH3 Cl over various Cu-based catalyst particles to substantially create macropores within the unreacted Si accompanying with carbon deposition to generate porous Si/C composites. Taking advantage of the interconnected porous structure and conductive carbon-coated layer after simple post treatment, these composites as anodes exhibit high reversible capacity and long cycle life. It is expected that by integrating the organosilane synthesis process and controlling reaction conditions, the manufacture of porous Si-based anodes on an industrial scale is highly possible.

Shape-controlled synthesis of Cu2O microparticles and their catalytic performances in the Rochow reaction

We report the preparation of Cu2O microparticles with different shapes, by simple hydrolyzation and reduction of copper acetate with glucose in a mixture of water–ethanol solvent. The effect of the synthesis conditions on the shape of the Cu2O microparticles and their catalytic properties in the Rochow reaction were investigated. The samples were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, temperature-programmed reduction, and thermogravimetric analysis. Cu2O microparticles with different shapes, such as hexahedron, ananas-like, sphere-like, and star-like shapes, with particle sizes of 2–4 μm, were obtained by tuning the volume ratio of water : ethanol. The hexahedron Cu2O microparticles were found to exhibit the best catalytic performance for the synthesis of dimethyldichlorosilane via the Rochow reaction. This work should be helpful in the design and development of novel copper catalysts for organosilane synthesis and understanding their catalytic roles.

Preparation of hierarchical dandelion-like CuO microspheres with enhanced catalytic performance for dimethyldichlorosilane synthesis

Hierarchical dandelion-like CuO (HD–CuO) microspheres composed of nanoribbons were prepared via a facile hydrothermal method. The samples were characterized by nitrogen adsorption, X-ray diffraction, temperature-programmed reduction, thermogravimetric analysis, transmission electron microscopy and scanning electron microscopy. It was found that the reaction temperature, reaction time and reagent amounts had a significant effect on the morphology and structure of HD–CuO. The obtained HD–CuO microspheres possessed a surface area of 10.6–57.5 m2 g−1 and a diameter of 3–6 μm. In the formation process, ethylene glycol was adsorbed on the surface of the CuO nanoribbons and it acted as the structure-directing agent and thereafter the CuO nanoribbons were self-assembled into HD–CuO. The investigation of the Rochow reaction showed that the HD–CuO catalyst had a better catalytic performance in dimethyldichlorosilane synthesis than the commercial CuO microparticles and commercial CuO–Cu2O–Cu catalyst, owing to its well-developed hierarchically porous structure and higher specific surface area, leading to the increased contact interface among reaction gas, solid catalyst and solid silicon, together with enhanced mass transportation.

Graphitized porous carbon microspheres assembled with carbon black nanoparticles as improved anode materials in Li-ion batteries

We report the facile preparation of graphitized porous carbon microspheres (GPCMs) by the spray drying technique using carbon black (CB) nanoparticles as the primary carbon resource and sucrose as the binder, followed by graphitization at 2800 °C. The samples were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, nitrogen adsorption, thermogravimetric analysis, and Raman spectroscopy. It is found that the GPCMs with a size of 5–20 μm delivered a reversible capacity of 459 mA h g−1 at the current density of 50 mA g−1 after 100 cycles, much higher than that of the commercial graphite microspheres (GMs) (372 mA h g−1). More importantly, GPCMs exhibited excellent rate performances with a capacity of 338 and 300 mA h g−1 at the current densities of 500 and 1000 mA g−1 respectively, superior to those of GMs (200 and 100 mA h g−1). The excellent electrochemical properties of GPCMs originate from its unique structure, which is composed of core–shell nanoparticles with the graphitized carbon core derived from CB nanoparticles and the hard carbon shell generated from sucrose, providing more lithium ion storage sites, higher electronic conductivity, and fast ion diffusion. This work opens a simple way to large-scale production of new carbon anode materials with a low cost and good performance for Li-ion batteries.

Yolk Bishell MnxCo1-xFe2O4 Hollow Microspheres and Their Embedded Form in Carbon for Highly Reversible Lithium Storage

The yolk-shell hollow structure of transition metal oxides has many applications in lithium-ion batteries and catalysis. However, it is still a big challenge to fabricate uniform hollow microspheres with the yolk bishell structure for mixed transition metal oxides and their supported or embedded forms in carbon microspheres with superior lithium storage properties. Here we report a new approach to the synthesis of manganese cobalt iron oxides/carbon (MnxCo1-xFe2O4 (0 ≤ x ≤ 1)) microspheres through carbonization of Mn(2+)Co(2+)Fe(3+)/carbonaceous microspheres in N2, which can be directly applied as high-performance anodes with a long cycle life for lithium storage. Furthermore, uniform hollow microspheres with a MnxCo1-xFe2O4 yolk bishell structure are obtained by annealing the above MnxCo1-xFe2O4/carbon microspheres in air. As demonstrated, these anodes exhibited a high reversible capacity of 498.3 mAh g(-1) even after 500 cycles for Mn0.5Co0.5Fe2O4/carbon microspheres and 774.6 mAh g(-1) over 100 cycles for Mn0.5Co0.5Fe2O4 yolk bishell hollow microspheres at the current density of 200 mA g(-1). The present strategy not only develops a high-performance anode material with long cycle life for lithium-ion batteries but also demonstrates a novel and feasible technique for designed synthesis of transition metal oxides yolk bishell hollow microspheres with various applications.

Facile solvothermal synthesis of porous cubic Cu microparticles as copper catalysts for Rochow reaction.

Porous cubic Cu microparticles were synthesized by a facile solvothermal method using Cu(CH(3)COO)(2)·H(2)O as the Cu precursor and NaOH in a solution containing ethanol, ethylene glycol, and water. The synthesis conditions were investigated and a growth process of porous cubic Cu microparticles was proposed. The catalytic properties of the porous Cu microparticles as model copper catalysts for Rochow reaction were explored. The samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, temperature-programmed reduction, and nitrogen adsorption. It was found that the morphology and structure of the porous cubic Cu microparticles are highly dependent on the reaction time and temperature as well as on the amount of reactants added. Compared to the commercial Cu microparticles with irregular morphology and dense internal structure, porous cubic Cu microparticles show much higher dimethyldichlorosilane selectivity and Si conversion via Rochow reaction, which are attributed to the enhanced formation of active Cu(x)Si phase and gas transportation in the presence of the pore system within microparticles, demonstrating the significance of the pore structure of the copper catalysts in catalytic reactions of organosilane synthesis.

Flower-like CuO microspheres with enhanced catalytic performance for dimethyldichlorosilane synthesis{

Flower-like CuO microspheres synthesized by a facile hydrothermal method were found to be an effective catalyst for the Rochow reaction with a higher dimethyldichlorosilane selectivity and Si conversion because of the enhanced formation of an active CuxSi phase and mass transport.

Amorphous silicon-carbon nanospheres synthesized by chemical vapor deposition using cheap methyltrichlorosilane as improved anode materials for Li-ion batteries.

We report the preparation and characterization of amorphous silicon-carbon (Si-C) nanospheres as anode materials in Li-ion batteries. These nanospheres were synthesized by a chemical vapor deposition at 900 °C using methyltrichlorosilane (CH3SiCl3) as both the Si and C precursor, which is a cheap byproduct in the organosilane industry. The samples were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, nitrogen adsorption, thermal gravimetric analysis, Raman spectroscopy, and X-ray photoelectron spectroscopy. It was found that the synthesized Si-C nanospheres composed of amorphous C (about 60 wt%) and Si (about 40 wt%) had a diameter of 400-600 nm and a surface area of 43.8 m(2) g(-1). Their charge capacities were 483.6, 331.7, 298.6, 180.6, and 344.2 mA h g(-1) at 50, 200, 500, 1000, and 50 mA g(-1) after 50 cycles, higher than that of the commercial graphite anode. The Si-C amorphous structure could absorb a large volume change of Si during Li insertion and extraction reactions and hinder the cracking or crumbling of the electrode, thus resulting in the improved reversible capacity and cycling stability. The work opens a new way to fabricate low cost Si-C anode materials for Li-ion batteries.