Stable cycling of double-walled silicon nanotube battery anodes through solid-electrolyte interphase control

Although the performance of lithium ion-batteries continues to improve, their energy density and cycle life remain insufficient for applications in consumer electronics, transport and large-scale renewable energy storage. Silicon has a large charge storage capacity and this makes it an attractive anode material, but pulverization during cycling and an unstable solid-electrolyte interphase has limited the cycle life of silicon anodes to hundreds of cycles. Here, we show that anodes consisting of an active silicon nanotube surrounded by an ion-permeable silicon oxide shell can cycle over 6,000 times in half cells while retaining more than 85% of their initial capacity. The outer surface of the silicon nanotube is prevented from expansion by the oxide shell, and the expanding inner surface is not exposed to the electrolyte, resulting in a stable solid-electrolyte interphase. Batteries containing these double-walled silicon nanotube anodes exhibit charge capacities approximately eight times larger than conventional carbon anodes and charging rates of up to 20C (a rate of 1C corresponds to complete charge or discharge in one hour).     

Synthetically programmable nanoparticle superlattices using a hollow three-dimensional spacer approach

Crystalline nanoparticle arrays and superlattices with well-defined geometries can be synthesized by using appropriate electrostatic, hydrogen-bonding or biological recognition interactions. Although superlattices with many distinct geometries can be produced using these approaches, the library of achievable lattices could be increased by developing a strategy that allows some of the nanoparticles within a binary lattice to be replaced with 'spacer' entities that are constructed to mimic the behaviour of the nanoparticles they replace, even though they do not contain an inorganic core. The inclusion of these spacer entities within a known binary superlattice would effectively delete one set of nanoparticles without affecting the positions of the other set. Here, we show how hollow DNA nanostructures can be used as 'three-dimensional spacers' within nanoparticle superlattices assembled through programmable DNA interactions. We show that this strategy can be used to form superlattices with five distinct symmetries, including one that has never before been observed in any crystalline material.     

Low temperature oxidation of n-butylcyclohexane

n-Butylcyclohexane, a possible surrogate component for petroleum- and coal-derived jet fuels, was oxidized in a flow reactor through the low temperature region from 600 to 820 K while other inlet conditions were held constant (0.8 MPa pressure, 0.120 s residence time, and 0.38 equivalence ratio). CO, CO₂, and O₂ were measured over the entire range of temperatures and stable intermediate species were collected at five temperatures and analyzed using a gas chromatograph/flame ionization detector/mass spectrometer. The measured species indicated that the n-butyl chain and the cyclohexane ring interact at low temperatures and result in low temperature reactivity similar to linear alkanes. At similar inlet conditions (0.8 MPa pressure, 0.120 s residence time, and 0.30 equivalence ratio), methylcyclohexane and n-butylbenzene, each neat, were oxidized in the reactor from 600 to 800 K and no reactivity was observed. This indicated the importance of the alkyl chain in low temperature oxidation of alkylcyclohexanes. To confirm that current understanding of low temperature oxidation chemistry of alkanes applies for n-butylcyclohexane, a preliminary reaction set, composed of 80 reactions and 42 species, was developed and incorporated into an existing high temperature jet fuel surrogate model. The new reaction scheme required calculation of thermochemistry for several compounds. The combined model predicts the overall low temperature reactivity of n-butylcyclohexane oxidation at the experimental conditions.     

Solid polymer electrolytes with sulfur based ionic liquid for lithium batteries

The electrochemical properties of a solid hybrid polymer electrolyte for lithium batteries based upon tri-ethyl sulfonium bis(trifluorosulfonyl) imide (S₂TFSI), lithium TFSI, and poly(ethylene oxide) (PEO) is presented. We have synthesized homogenous freestanding films that possess low temperature ionic conductivity and wide electrochemical stability. The hybrid electrolyte has demonstrated ionic conductivity of 0.117 mS cm⁻¹ at 0 °C, and 1.20 mS cm⁻¹ at 25 °C. At slightly elevated temperature ionic conductivity is on the order of 10 mS cm⁻¹. The hybrid electrolyte has demonstrated reversible stability against metallic lithium at the anodic interface and >4.5 V vs. Li/Li⁺ at the cathodic interface.     

An alternative to the search for single polymorphisms: Toward molecular personality scales for the five-factor model.

There is growing evidence that personality traits are affected by many genes, all of which have very small effects. As an alternative to the largely unsuccessful search for individual polymorphisms associated with personality traits, the authors identified large sets of potentially related single nucleotide polymorphisms (SNPs) and summed them to form molecular personality scales (MPSs) with from 4 to 2,497 SNPs. Scales were derived from two thirds of a large (N = 3,972) sample of individuals from Sardinia who completed the Revised NEO Personality Inventory (P. T. Costa, Jr., & R. R. McCrae, 1992) and were assessed in a genomewide association scan. When MPSs were correlated with the phenotype in the remaining one third of the sample, very small but significant associations were found for 4 of the 5e personality factors when the longest scales were examined. These data suggest that MPSs for Neuroticism, Openness to Experience, Agreeableness, and Conscientiousness (but not Extraversion) contain genetic information that can be refined in future studies, and the procedures described here should be applicable to other quantitative traits. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Experimental Performance of Full-Depth Precast, Prestressed Concrete Overhang, Bridge Deck Panels

The performance of a new full-depth precast overhang panel system for concrete bridge decks is investigated experimentally. In contrast to conventional cast-in-place deck overhangs, the proposed full-depth precast overhang system has the potential to speed up construction, reduce costs, and improve safety. Load-deformation behavior up to factored design load limits is first investigated. The panel is then loaded near its edge to examine the collapse capacity and the associated failure modes—particularly the influence of panel-to-panel connections that exist, transverse to the bridge deck axis. Comparative tests are also conducted with a conventional cast-in-place overhang system. When compared to the conventional cast-in-place overhang behavior, the experimental results show that the precast full-depth overhang introduces different behavior modes, largely due to the influence of the partial depth panel-to-panel connection, which reduces the capacity by some 13%.     

For want of a nail: How absences cause events.

Causation by omission is instantiated when an effect occurs from an absence, as in The absence of nicotine causes withdrawal or Not watering the plant caused it to wilt. The phenomenon has been viewed as an insurmountable problem for process theories of causation, which specify causation in terms of conserved quantities, like force, but not for theories that specify causation in terms of statistical or counterfactual dependencies. A new account of causation challenges these assumptions. According to the force theory, absences are causal when the removal of a force leads to an effect. Evidence in support of this account was found in 3 experiments in which people classified animations of complex causal chains involving force removal, as well as chains involving virtual forces, that is, forces that were anticipated but never realized. In a 4th experiment, the force theory's ability to predict synonymy relationships between different types of causal expressions provided further evidence for this theory over dependency theories. The findings show not only how causation by omission can be grounded in the physical world but also why only certain absences, among the potentially infinite number of absences, are causal. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A close look at valences in hexahedral element meshes

This paper discusses using valences in objective functions for topological modification of 3D hexahedral meshes. For topological optimization of 2D quadrilateral meshes, node valence (i.e. number of element edges attached to each node) is used to maximize the number of regular nodes (i.e. nodes with four attached edges). Difficulties in developing 3D hexahedral local topology modifications have limited the success of hexahedral topology optimization, although published literature suggests using an object function based on node valence. However, in this paper, we show that node valence is not a consistent measure of good hexahedral element topology, and objective functions based on node valence can lead to element topology, which will only admit concave element shapes. Instead, we propose that objective functions based on edge valence (i.e. number of quadrilateral faces attached to each element edge) will provide a consistent measure of element topology. Copyright © 2010 John Wiley & Sons, Ltd.