Showing papers by "Yong Wang published in 2004"

Molten Salt Synthesis of Tin Oxide Nanorods: Morphological and Electrochemical Features

Abstract: This article reports the nonhydrothermal synthesis of SnO2 nanorods at moderate temperatures (320 or 700 °C), and the application of these nanorods as a Li storage compound for Li-ion batteries. The 15 nm diameter high aspect ratio (∼50−100) SnO2 nanorods prepared at 700 °C were fabricated as Li-ion battery anodes and tested. They exhibited good capacity (∼700 mAh/g nominal in the 5 mV to 1 V range) and extended cyclability for a tin-based anode. More interestingly was the observation of a capacity of ∼1100 mAh/g in the 5 mV to 2 V window that exceeds the theoretical capacity of SnO2. SEM and TEM characterizations revealed substantial morphological changes in the nanorods during cycling. A few possible reasons for the high capacity and the morphological changes are provided.

Tin Nanoparticle Loaded Graphite Anodes for Li-Ion Battery Applications

Abstract: Nearly monosized Sn nanoparticles were produced by an in situ prepared single-source molecular precursor approach. The experimental conditions in the NaBH 4 reduction of (phen)SnCl 4 (phen = 1, 10 phenanthroline) in water were carefully controlled to produce two different particle size ranges, 2-5 nm (mean: 3.5 nm, standard deviation: 0.8 nm) and 7-13 nm (mean: 10.0 nm, standard deviation: 1.7 nm). The Sn nanoparticles were subsequently dispersed in graphite (KS6) and the application of the resulting nanocomposites as an active anode material for Li-ion batteries was explored. The graphite-Sn nanocomposites showed significant improvement in the cyclability of Sn over previously reported results. The cyclability improvement is believed to be due to the smallness of the Sn particles and their uniform distribution in a soft matrix (graphite) which, in addition to being a capable Li + host, could also effectively buffer the specific volume changes in Sn-based Li storage compounds during charging (Li + insertion) and discharging (Li + extraction) reactions.

Controlled Synthesis of V-shaped SnO2 Nanorods

Abstract: This report details the preparation of V-shaped SnO2 nanorods with an angle of 112.1° between the arms. The nanorods were produced by heating 1,10 phenanthroline (phen)-capped Sn nanoparticles (2−5 nm) in a NaCl flux. The use of both phen and NaCl flux were indispensable in forming long V-shaped structures. XRD, SEM, TEM, and HRTEM characterizations of the nanorods confirmed that the rods were crystalline SnO2 with a twin structure (twin plane of (101) and twin direction of [101]) at the V-junction. The diameters of the nanorods were nearly monodispersed with mean values of 48.4 and 13.2 nm depending on the synthesis conditions.

Microemulsion syntheses of Sn and SnO2-Graphite nanocomposite anodes for Li-ion batteries

Abstract: Nanostructured SnO 2 , SnO 2 -graphite, and Sn-graphite composites were prepared by microemulsion techniques using Tergitol 15-S-5 as the surfactant. The particle size of the pristine SnO 2 nanoparticles was typically between 12 and 14 nm. For the composites, Sn and SnO 2 nanoparticles 7-10 nm in size with narrow size distribution were uniformly dispersed on graphite, indicating the positive effect of graphite in maintaining smaller particle size. These Sn-based nanocomposites are multiple Li host systems with good cycling performance in Li-ion battery applications. The improved cyclability is perceived to be a combination of the use of well dispersed Sn or SnO 2 nanoparticles resistant to particle agglomeration, and the presence of a soft graphite matrix to buffer the volume changes in the Li-Sn reactions. In addition, the Sn-graphite nanocomposites exhibited a SnO-shell-Sn-core structure and slightly lower first cycle capacity losses.

A microemulsion-based preparation of tin/tin oxide core/shell nanoparticles with particle size control

Abstract: Nearly monodispersed tin/tin oxide core/shell nanoparticles were prepared by a reverse microemulsion technique. A phenanthroline–tin chloride complex was used in an optimized microemulsion system to obtain small particle size and good size control (mean = 3.2 nm, standard deviation = 0.5 nm). Preparation in the absence of phenathroline in an otherwise identical microemulsion composition would result in larger particles and a broader size distribution (mean = 7.4 nm, standard deviation = 1.8 nm). The nanoparticles were extensively characterized and the sequence of events leading to the nanoparticle formation is postulated.