Wenfeng Ren

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.

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.

Carbon-coated porous silicon composites as high performance Li-ion battery anode materials: can the production process be cheaper and greener?

As the most promising next-generation lithium-ion battery anode materials, porous silicon-based materials are attracting great attention nowadays, mainly because of silicons exceptionally high lithium storage capacity. However, how to realize the large-scale manufacture of these materials at low cost still remains a big challenge. In this work, we report the direct preparation of porous Si materials from metallurgical-grade Si in an autoclave, which is the most environmentally friendly route to produce alkoxysilane monomers in the organic silicon industry. In this reaction, Cu-based catalysts catalyze the reaction of Si particles with alcohols to create a porous structure within Si, followed by carbon deposition via the chemical vapor deposition method. The micro-morphology and -structure of the porous Si materials can be well tuned by adjusting the synthesis conditions. When used as the anode materials for lithium ion batteries, the charge capacity of the obtained porous Si/C materials was 1240 mA h g(-1) at a current density of 50 mA g(-1) after 50 cycles, much higher than that of the commercial graphite. This work provides an economic and scalable approach to the preparation of porous Si/C anode materials from commercial Si powders for lithium ion batteries.

Effect of boron on structure and magnetic properties of magnetostrictive compound Dy0.7Pr0.3Fe2

Crystal structure, magnetic properties and magnetostriction of Dy0.7Pr0.3(Fe1-xBx)(2) (0less than or equal toxless than or equal to0.20) have been investigated by means of x-ray diffraction, ac initial susceptibility, a vibrating sample magnetometer, and a standard strain technique. The matrix of Dy0.7Pr0.3Fe2 alloy consists of (Dy,Pr)Fe-2 phase with a cubic MgCu2-type structure and some amount of (Dy,Pr)Fe-3 phase with a rhombohedral PuNi3-type structure. The introduction of boron effectively restrains the emergence of the iron-rich phase and thus decreases the amount of (Dy,Pr)Fe-3 phase. Dy0.7Pr0.3(Fe1-xBx)(2) alloy with x=0.05 contains small amount of (Dy,Pr)(Fe,B)(3) phase, and those with x=0.10 and x=0.15 are essentially of a single (Dy,Pr)(Fe,B)(2) phase. An unidentified minor phase appears when x=0.20. The lattice parameter of (Dy,Pr)(Fe,B)(2) phase decreases monotonically with the boron substitution up to x=0.20, indicating that the boron atoms occupy the substitutional sites. The Curie temperature for (Dy,Pr)(Fe,B)(2) phase obviously increases compared with the boron free one. The saturation magnetization at room temperature increases with increasing boron content for the alloys studied, suggesting that the partial boron substitution is beneficial to the increment of the exchange interactions in the Dy0.7Pr0.3Fe2 system. The increment of the magnetization originates from the decrement of iron content, because the Fe moment that aligns antiparallel with the Dy moment almost keeps constant in this system. Boron substitution for iron increases the lattice distortion and anisotropy, thus causes the decrease of the linear magnetostriction lambda(a)=lambda(parallel to)-lambda(perpendicular to) at the room temperature

Mn0.5Co0.5Fe2O4 nanoparticles highly dispersed in porous carbon microspheres as high performance anode materials in Li-ion batteries.

We report the preparation of Mn(0.5)Co(0.5)Fe2O4 (MCFO) nanoparticles highly dispersed within porous carbon microspheres as anodes for Li-ion batteries. In situ growth of MCFO nanoparticles (5-20 nm) on the surface of carbon black (CB) and graphitized carbon black (GCB) nanoparticles was conducted via a hydrothermal method to form MCFO-CB and MCFO-GCB composites, respectively, which were employed as building blocks to assemble MCFO-CB and MCFO-GCB porous microspheres (PM) with a size of 5-30 μm by the spray drying technique using sucrose as a binder, and followed by carbonization in N2 (labeled as MCFO-CB-PM and MCFO-GCB-PM, respectively). Compared with the pure MCFO, MCFO-CB, and MCFO-GCB, both MCFO-CB-PM and MCFO-GCB-PM showed a significantly improved electrochemical performance. This is attributed to their unique porous structure, in which, the abundant pores promote the diffusion of Li-ion and electrolyte solution, the microspherical morphology enhances the electrode-electrolyte contact, and the carbon substrates from CB (and GCB) and sucrose substantially prevent the aggregation of MCFO nanoparticles and buffer the volume change. Particularly, MCFO-GCB-PM exhibits the best rate performance and excellent cycling stability because of the high graphitization degree of GCB. This work opens up an effective route for large scale fabrication of metal oxide/carbon porous microspheres as anode materials for potential applications in the new generation of Li-ion batteries.

Preparation of porous carbon microspheres anode materials from fine needle coke powders for lithium-ion batteries

A large amount of fine carbon powders (graphite and cokes) are generated as the solid waste in the manufacture of carbon-based materials in industry. How to utilize these abundant powders to generate products with high value still remains a big challenge. Herein, we report the preparation of porous carbon microspheres (PCMs) employing waste non-graphitized needle coke and graphitized needle coke as the fine carbon powder representatives, demonstrating their use as anode materials for lithium-ion batteries. It was found that the graphitized PCMs had a size of 8–30 μm and surface areas between 50 and 120 m2 g−1. When used as the anode materials, their charge capacity at the current density of 50 mA g−1 was comparable to that of the commercial graphite microspheres, but they exhibited higher rate performance.

Magnetic properties and exchange coupling of nanocomposite (Nd,Y)2Fe14B/α-Fe

Magnetic properties and exchange couplings of nanocomposite (Nd,Y)2Fe14B/α-Fe magnets prepared by mechanical milling have been investigated at low temperatures. With decreasing temperature, due to Y substitution for Nd, an extension of the exchange coupling length in nanocomposite magnets occurs in a wider temperature range. This can be attributed a decreasing anisotropy of the hard-magnetic phase so that more soft-magnetic grains participate the exchange coupling. Close to 135 K, due to the spin reorientation, the hard magnetic phase is not more uniaxail, which leads to a drastic decrease of the magnetic properties of the Nd2Fe14B-based nanocomposite magnets.

Structure and magnetic properties of nanostructured Pr1−xGdxCo5(x=0–1) powders prepared by mechanical alloying

The phase components, structures, and magnetic properties of Pr1-xGdxCo5 (x=0-1) powders synthesized by mechanical alloying and subsequent annealing have been investigated systematically. The optimal magnetic properties, with a coercivity of 12.5 kOe, a remanence ratio of 0.72, and a maximum energy product of 12.7 MGOe, have been obtained from PrCo5 powders milled for 5 h and annealed at 700 degreesC for 2 min. The remanence and maximum energy product were decreased monotonically with increasing Gd content, whereas the coercivity was increased, reaching a maximum of 23.7 kOe in Pr0.2Gd0.8Co5 powders. X-ray diffraction and transmission electron microscopy observations reveal that an uniform (Pr,Gd)Co-5/(Pr,Gd)(2)Co-17 nanostructure with an average grain size of 20-30 nm forms in the powders annealing at 700 degreesC. The obtained magnetic hardening apparently originates from the high anisotropy field of the hard (Pr,Gd)Co-5 phase and the uniform nanostructure developed by mechanical alloying and subsequent annealing

Enhanced magnetostrictive effect in epoxy-bonded TbxDy0.9-xNd0.1(Fe0.8Co0.2)(1.93) pseudo 1-3 particulate composites

The spin configuration and spontaneous magnetostriction λ111 of TbxDy0.9−xNd0.1(Fe0.8Co0.2)1.93 (0.20 ≤ x ≤ 0.60) alloys have been investigated. The easy magnetization direction (EMD) at room temperature was observed towards the 〈111〉 axis when 0.40 ≤ x ≤ 0.60, accompanied by a rhombohedral distortion with large spontaneous magnetostriction coefficients λ111, which increases from 1640 ppm for x = 0.40 to 1900 ppm for x = 0.60. The strong 〈111〉-oriented pseudo 1–3 particulate composite was fabricated by embedding and aligning particles in a passive epoxy matrix under an applied magnetic field. An enhanced magnetostrictive effect, the large low-field magnetostriction, λa, as high as 480 ppm at 3 kOe, was obtained for the sample of x = 0.40, in an excess of 75% of its polycrystalline alloy although it only contains 27 vol. % alloy particles. This enhanced effect can be attributed to its low magnetic anisotropy, anisotropic magnetostrictive nature (e.g., λ111 ≠ λ100, 〈111〉EMD), chain structure, and the 〈111〉-...

Synthesis of porous microspheres composed of graphitized carbon@amorphous silicon/carbon layers as high performance anode materials for Li-ion batteries

We report in situ growth of amorphous silicon/carbon (Si/C) layers on graphitized carbon black (GCB) particles in porous microspheres (PMs) for formation of novel GCB@Si/C PMs as high performance anode materials. The preparation included spray drying, KOH activation and chemical vapor deposition at 900 °C, and used methyltrichlorosilane as both the Si and C precursor, which is a cheap byproduct in the organosilane industry. The obtained samples were characterized by X-ray diffraction, thermogravimetric analysis, nitrogen adsorption, transmission electron microscopy, and scanning electron microscopy. Compared with the bare GCB PMs, the GCB@Si/C PMs showed a significantly enhanced electrochemical performance with high lithium storage capacity and excellent cycling stability (the discharge capacity of GCB@Si/C-3 PMs and GCB@Si/C-6 PMs is maintained at 587.2 and 729.7 mA h g−1 after 200 cycles at a current density of 100 mA g−1), because the unique interconnected porous structure within the microspheres could absorb a large portion of Si volume change during Li insertion and extraction reactions, promote the diffusion of Li-ion and electrolyte solution, hinder the cracking or crumbling of the electrode, and additionally, the GCB and amorphous C provide high conductive electron pathway. This work opens a new way for fabrication of Si/C nanocomposites as anode materials for Li-ion batteries.