Bulletin of the American Physical Society
65th Annual Gaseous Electronics Conference
Volume 57, Number 8
Monday–Friday, October 22–26, 2012; Austin, Texas
Session LW1: Nanotechnologies II |
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Chair: Steven Girshick, University of Minnesota Room: Amphitheatre 204 |
Wednesday, October 24, 2012 1:30PM - 2:00PM |
LW1.00001: Si-O-Cx nano-composite negative electrodes for next generation lithium ion batteries formed by plasma spray PVD Invited Speaker: Makoto Kambara Silicon is a promising material for negative electrode of lithium ion batteries (LIB) owing to its high theoretical capacity. However, this material inevitably suffers from huge volume change as large as 400$\% $ during charge/discharge process, i.e. alloying and de-alloying with lithium ions, which causes pulverization of the electrode itself and thus the loss of the electric path within the electrode, only after several charge cycles. Approaches to overcome this difficulty have been reported from the structural control point of views, such as design of materials at nanometer length scale, including nano-porous structure, nanowire structure and composites with other elements. Practically speaking, such a nano-structuring has to be also done by the process that has the potential to be developed to meet the industrial throughputs in future. With this in mind, we have demonstrated plasma spraying for production of the Si-Cx nano-composite powders and showed their potential as negative electrode by the reasonably high capacity and cycle stability. Another advantage of this process is that cheap raw materials, such as metallurgical Si (mg-Si), can be used as Si source so that industry compatible low cost is also anticipated. With these as background, we attempted plasma spraying with SiO powders as another Si source and the fundamental battery properties were characterized in comparison with the case with mg-Si powders. In brief, aggregate powders with 0.1-5$\mu $m in size having 20-50 nm a-SiO as the primary particle was produced by plasma spraying from 15$\mu $m feedstock SiO powders at the feeding rate of 2.4 g/min. Upon addition of CH4 gas, reduction and disproportionation reaction of SiO is promoted, leading to the formation of nano-composite a-SiOx particle with $<$10 nm Si at its core. The half coin cells with these powders as electrode have shown 1000 mAh/g after 50 cycles with reasonable retention efficiency of $>$99.7{\%}. [Preview Abstract] |
Wednesday, October 24, 2012 2:00PM - 2:15PM |
LW1.00002: Plasma Synthesis of Silicon Nanocrystals for Ligand-less Colloidal Stability Lance Wheeler, Uwe Kortshagen Colloidal synthesis of prevailing semiconductor nanocrystals (NCs) requires long-chain organic ligands that provide steric stabilization. As these ligands hinder charge carrier transport when NCs are cast into thin films, significant efforts have focused on ligand exchange or removal schemes either in solution or during film assembly. Here we present a new mechanism to produce stable NC colloids without the need for any ligands. Silicon NCs are tailored in a gas phase plasma approach with a heterogeneous chlorine/hydrogen surface coverage to achieve an acidic surface. When the NCs are dispersed in solvents with hard donor groups, acid-base surface interactions induce stabilizing solvation layer around the NCs. In a set of experiments, electrostatic and steric stabilization are ruled out and evidence for the solvation layer formation is found. A set of criteria to achieve NC solvation is developed. Crack-free electronically coupled NC films are produced from these ligand-less NC colloids. [Preview Abstract] |
Wednesday, October 24, 2012 2:15PM - 2:30PM |
LW1.00003: Impacts of plasma fluctuation on growth of nanoparticles in low pressure reactive VHF discharge plasmas Masaharu Shiratani, Kunihiro Kamataki, Yasuo Morita, Hyunwoong Seo, Naho Itagaki, Giichiro Uchida, Kazunori Koga Here we discuss impacts of plasma fluctuation on nanostructure formation using plasmas. We studied the effects of plasma fluctuation on the growth of nanoparticles in capacitively-coupled VHF discharges with amplitude modulation (AM) using 2 dimensional laser light scattering method [1]. AM gives an artificial plasma fluctuation. Nanoparticles grow more slowly for higher AM levels, which causes the density of nanoparticles to increase by 100{\%}, their size to decrease by 23{\%}, and narrower size dispersion. The increase in the nucleation density of nanoparticles by AM causes a decrease in the radical flux to a nanoparticle. Eventually we obtained a diagram of the three particle growth modes of positive feedback, negative feedback, and independent ones. We also have developed a simple theory of particle growth in reactive plasmas. The theory predicts experimental results well. Our approach can be applied to realize precise control of a wide variety of nanostructure formations.\\[4pt] [1] K. Kamataki, et al., J. Inst. 7 (2012) C04017. [Preview Abstract] |
Wednesday, October 24, 2012 2:30PM - 2:45PM |
LW1.00004: ABSTRACT WITHDRAWN |
Wednesday, October 24, 2012 2:45PM - 3:00PM |
LW1.00005: ABSTRACT WITHDRAWN |
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