Fe2O3 nanobelts/carbon nanotubes (CNTs) composites were successfully synthesized by a novel homogeneous precipitation of FeC2O4 on CNTs followed with thermal annealing. The bundle-like Fe2O3 nanobelts, with a width of 10nm, are homogeneously dispersed on CNTs. Compared to the bare Fe2O3 nanobelts, the Fe2O3 nanobelts/CNTs composites showed significantly improved electrochemical performance which can be attributed to their uniform conducting networks structure. The Fe2O3 nanobelts/CNTs composites delivered an initial reversible capacity of 847.5 mAh g−1 at current density of 100mAg−1, and exhibited excellent cycling performance with a reversible capacity of 865.9 mAh g−1 after 50 cycles. Meanwhile, the composites also maintained a high reversible capacity of 442.1 mAh g−1 even at a current density up to 4 A g−1.

The key factors influencing the low-temperature electrochemical performances of LiFePO4 cathode materials are systematically investigated by measuring and comparing the amount of surface carbon, particle size, and conductivities of LiFePO4, LiFePO4/C and electrolyte in the temperatures range of -20 to 40 degrees C. It is found that the low-temperature electrochemical performance of the material is improved obviously by coating the surface of LiFePO4 with carbon. At -20 degrees C, the discharge specific capacity of LiFePO4/C with 4 wt% surface carbon is 81.4 mAh/g, while the uncoated LiFePO4 only delivers the discharge specific capacity of 27.7 mAh/g. The low-temperature electrochemical performance of LiFePO4/C has no significant change as increasing the carbon content, but is further improved by reducing the particle size. In order to understand the difference of low-temperature electrochemical performance between the carbon-coated and uncoated LiFePO4 cathodes, the ionic conductivity of electrolyte, the electronic/ionic conductivities of LiFePO4 and LiFePO4/C at various temperatures were measured. The electronic conductivity of LiFePO4 with 4.9 x 10(-11) S/cm at -20 degrees C is found to be responsible for its poor low-temperature electrochemical performance. However, for the LiFePO4/C, the low-temperature electrochemical performance is mainly determined by its ionic conductivity, therefore, the decrease of the particle size can increase the low-temperature electrochemical performance. (C) 2014 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Anode material for lithium-ion battery based on Sn/carbon nanotube (CNT) composite is synthesized via a chemical reduction method. The Sn/CNT composite is characterized by thermogravimetry, X-ray diffraction, and transition electron microscopy. The Sn/CNT composite delivers high initial reversible capacity of 630.5 mAh g −1 and exhibits stable cycling performance with a reversible capacity of 413 mAh g −1 at the 100th cycle. The enhanced electrochemical performance of the Sn/CNT composite could be mainly attributed to the well dispersion of Sn nanoparticles on CNT and partially filling Sn nanoparticles inside the CNT. It is proposed that the chemical treatment of CNT with concentrated nitric acid, which cuts carbon nanotube into short pieces and increases the amount of oxygen-functional groups on the surface, plays an important role in the anchoring of Sn nanoparticles on carbon nanotube and inhibiting the agglomeration of Sn nanoparticles during the charge–discharge process.

LiFePO4/C nanocomposites are synthesized by a propylene oxide-assisted fast sol–gel method using FeCl3, LiNO3, NH4H2PO4, and sucrose as the starting materials. It was found that after adding propylene oxide into the solution containing the starting materials, a monolithic jelly-like FePO4 gel containing lithium and carbon source is generated in a few minutes without controlling the pH value of the solution and a time-consuming heating process. Propylene oxide plays a key role in the fast generation of the precursor gel. The final products of LiFePO4/C are obtained by sintering the dry precursor gel. The structures, micro-morphologies, and electrochemical properties of the LiFePO4/C composites are investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen adsorption–desorption analysis, electrochemical impedance spectrum, and charge–discharge cycling tests. The results indicate that the LiFePO4/C composite prepared by sintering the precursor gel at 680 °C for 5 h is about 30 nm in size with a meso-porous structure (the main pore size distribution is around 3.4 nm). It delivers 166.7 and 105.8 mAh g−1 at 0.2 and 30 C, respectively. The discharge specific capacity is 97.8 mAh g−1 even at 40 C. The cycling performance of the prepared LiFePO4/C composite is stable. The excellent electrochemical performance of the LiFePO4/C composite is attributed to the nano-sized and mesoporous structure of LiFePO4/C and the in-situ surface coating of the carbon. It was also found that propylene oxide is crucial for the generation of mesoporous and nano-structured LiFePO4/C.

An efficient anode with a superior high-rate capability and stability remains a challenge for development of high performance Li-ion batteries. We present a new concept by encapsulating 2 nm-sized SnO2 nanocrystals in the channels of carbon nanotubes (SnO2-in-CNTs). Characterization shows that the confined space does not only stabilize the small nanoparticles but also alleviates the stress caused by the large volume change of tin species during the charging-discharging process. In addition, well crystallized graphitic structure of CNTs with a positive curvature provides a good contact between SnO2 nanoparticles and graphene layers, and excellent electronic conductivity. As a result, SnO2-in-CNTs as an anode of lithium ion battery exhibit stable cyclability and superior high-rate capability relative to SnO2 nanoparticles dispersed on the outer walls of CNTs particularly under a high current density. The charge capacity remains about 560 mA h g(-1) after 50 cycles at 50 mA g(-1), and even around 400 mA h g(-1) at 1000 mA g(-1). Additionally, the facile preparation method we have developed makes such encapsulates appealing for further optimization and applications.

Non-graphitic carbon nanotubes (NGCNTs) are successfully prepared by carbonization of polypyrrole (PPy) nanotubes precursor synthesized via a self-assembly process. It is observed from transmission electron microscopy (TEM) that the diameter and length of the NGCNTs are 100–200nm and 2–10μm, respectively. The electrochemical performances of the NGCNTs are evaluated by cyclic voltammograms and galvanostatic discharge–charge cycling. The results show that NGCNTs deliver an initial reversible capacity of 635.7mAhg−1 at current density of 100mAg−1 with a high capacity retention ratio of 85.7% after 150 cycles. Even up to 4Ag−1, the reversible capacity of NGCNTs remains in 280.1mAhg−1. The improved performance of NGCNTs is attributed to the non-graphitic form, tubular morphology and cross-linked conducting networks. Therefore, it is a potential anode material for lithium-ion battery.

Porous SnO2 nanoflakes with loose-packed structure were synthesized by calcination of SnS2 precursors that were obtained through solvothermal method at low temperature. The as-obtained SnO2 product had a three-dimensional porous structure with relatively high specific surface area. It was found that the SnO2 nanoflakes inherited the morphology of precursor while numerous pores were formed after the annealing process. The combined techniques of X-ray diffraction, energy-dispersive spectrum, field emission scanning electron microscopy, and (high-resolution) transmission electron microscopy were used for characterization of the as-prepared SnO2 product. Moreover, the porous SnO2 nanoflakes with loose-packed structure could be used as gas sensors for detecting ethanol and acted as anode for lithium ion batteries. Our study shows that the as-prepared SnO2 nanoflakes not only exhibit good response and reversibility to ethanol gas but also display enhanced Li-ion storage capability.

Nanoflakes-built pyrite FeS2 microspheres were synthesized through a simple solvothermal process in mixed solvents of N, N-dimethytformamide and ethylene glycol without using any surfactant. Both the composition of the solvents and urea were key factors for the formation of the uniform products. It was found that the flake-like intermediate products transformed into FeS2 nanoflakes in situ in the early stage and Ostwald ripening growth mechanism would contribute to the uniformity of the final products. Electrochemical studies revealed that the nanoflakes-built pyrite FeS2 microspheres exhibited large lithium storage capacities. This method can be easily controlled and is expected to be extendable to the fabrication of other metal chalcogenides with controlled shape and structure.