Qiangqiang Tan

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.

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.

Reduction mechanism of natural ilmenite with graphite

Abstract Reduction of Bama ilmenite concentrate containing 49.78% TiO2 and 27.96% total Fe by graphite was studied using thermogravimetric analysis system under argon gas ambient from 850 to 1 400 °C. The reduction degree of Bama ilmenite is enhanced with increasing temperature and the molar ratio of carbon to oxygen, and the reaction rate varies with temperature and reduction time simultaneously. The phase transformation, chemical composition, microstructure and morphology of reduced samples were investigated by using X-ray diffractometry, scanning electron microscopy, and energy disperse spectroscopy, respectively. The high content of impurities in Bama ilmenite evidently bates the reduction of ilmenite. Forming the enrichment zone of manganese prevents complete reduction of Fe2+. The reduction products are mostly reduced iron, rutile, reduced rutiles, Ti3O5 and pseudobrookite solid solution. The reduction kinetics was also discussed. The results show that the reduction temperature is a key factor to control reaction rate.

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.

Enhancing the Electrocatalytic Property of Hollow Structured Platinum Nanoparticles for Methanol Oxidation Through A Hybrid Construction

The integration of different components into a hybrid nanosystem for the utilization of the synergistic effects is an effective way to design the electrocatalysts. Herein, we demonstrate a hybrid strategy to enhance the electrocatalytic property of hollow structured Pt nanoparticles for methanol oxidation reaction. This strategy begins with the preparation of bimetallic Ag-Pt nanoparticles with a core-shell construction. Element sulfur is then added to transform the core-shell Ag-Pt nanostructures into hybrid nanodimers consisting of Ag2S nanocrystals and remaining Pt domains with intact hollow interiors (Ag2S-hPt). Finally, Au is deposited at the surface of the Ag2S domain in each hetero-dimer, resulting in the formation of ternary Ag2S-Au-hPt nanocomposites with solid-state interfaces. The ternary nanocomposites exhibit enhanced electrocatalytic property toward methanol oxidation due to the strong electronic coupling between Pt and other domains in the hybrid particles. The concept might be used toward the design and synthesis of other hetero-nanostructures with technological importance.

Preparation of porous silicon/carbon microspheres as high performance anode materials for lithium ion batteries

We report the preparation of porous silicon/carbon microspheres (GPSCMs) by the ball milling and spray drying methods followed by carbonization and chemical vapor deposition processes, in which, the waste fine graphitized needle coke and silicon nanoparticles were employed as the carbon and silicon sources respectively, and sucrose as the binder. The samples were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, nitrogen adsorption, thermogravimetric analysis, and Raman spectroscopy. It was found that GPSCMs had spherical sizes of 8–30 μm and surface areas between 20 and 90 m2 g−1. When used as the anode materials for lithium ion batteries, the average charge capacity was 589 mA h g−1 at a current density of 50 mA g−1, much higher than that of the commercial graphite microspheres (GMs). Furthermore, GPSCMs exhibited much better rate performance than the commercial GMs, making them promising for use as the next generation anode materials in lithium ion batteries.

Rheological properties of nanometer tetragonal polycrystal zirconia slurries for aqueous gel tape casting process

The aim of the present work was to identify the conditions for the preparation of stable zirconia slurries with high solids content for the production of aqueous gel tape casting objects with improved properties. Influences of the powder and dispersant on the rheological properties were investigated. High stable low-viscosity nanoparticles zirconia suspensions were achieved. Nanometer-sized tetragonal polycrystal zirconia powder was synthesized by a new low-temperature environment-benign method. The oxide powders were confirmed to be 3Y-TZP single phase with tetragonal structure measured by X-ray diffraction analysis. Acryl amide (AM) and N,N′-methylene bisacrylamide (MBAM) have been used as organic monomer and cross-linker of the process, respectively. NH4PAA (M=5000–8000) has been used as polyelectrolyte dispersant. The electrokinetic behavior of nanometer-sized zirconia suspensions stabilized by various dispersant contents was studied. The result indicated the dispersant concentration greatly affected the surface charge of nanometer tetragonal zirconia powder. The isoelectric point (IEP) obviously changed from 8.1 to about 4.7 because of the addition of polyelectrolyte dispersant. To acquire stable low-viscosity slurries, the influences of several parameters on rheological behavior of nanosized tetragonal zirconia suspensions were investigated. It was found that for each factor, there exists an optimum range in which low viscosity was achieved for a slurry with high solid loading. For the slurry of 77 wt.% powder concentration with about 1.0 wt.% polyelectrolyte (based on the powder), the viscosity was 350 mPa s at the shear rate of 110 s−1. The slurry at the optimum conditions met the demands of aqueous gel tape casting process.

Multiple transition metal oxide mesoporous nanospheres with controllable composition for lithium storage

A general synthetic method based on a solvothermal route for the preparation of multiple transition metal oxide (MTMO) mesoporous nanospheres (ZnaNibMncCodFe2O4, 0 ≤ a, b, c, d ≤ 1, a + b + c + d = 1) with controllable composition and uniform size distribution has been developed. The as-prepared ZnaNibMncCodFe2O4 nanospheres are formed by self-assembly of nanocrystals with the size of 5–10 nm via structure-directing agents and mineralizer coordinating effect as well as optimization of the synthesis conditions. It has been identified that the addition of mineralizer is crucial for the control of the nucleation process when the metallic precursors are reduced; meanwhile the structure-directing agent is key to forming the mesoporous structure. A number of characterization techniques including X-ray diffraction, transmission electron microscopy, scanning electron microscopy, inductively coupled plasma optical emission spectrometry, temperature-programmed reduction, and nitrogen adsorption have been used to characterize the as-prepared mesoporous products. The overall strategy in this work extends the controllable fabrication of high-quality MTMO mesoporous nanospheres with designed components and compositions, rendering these nanospheres with promising potential for various applications (oxygen reduction reaction, magnetic performance, supercapacitor, lithium-ion batteries, and catalysis).