Failure Modes of Silicon Powder Negative Electrode in Lithium Secondary Batteries

Si composite negative electrodes for lithium secondary batteries degrade in the dealloying period with an abrupt increase in internal resistance that is caused by a breakdown of conductive network made between Si and carbon particles. This results from a volume contraction of Si particles after expansion in the previous alloying process. Due to the large internal resistance, the dealloying reaction is not completed while Si remains as a lithiated state. The anodic performance is greatly improved either by applying a pressure on the cells or loading a larger amount of conductive carbon in the composite electrodes.This work was partially supported by KOSEF through Research Center for Energy Conversion and Storage, and by the financial support of Center for Nanostructured Materials Technology under 21st Century Frontier R&D Programs of the Ministry of Science and Technology, Korea. Financial support from LG Chem. Ltd. is also acknowledged

Underpotential deposition of Cu on Au(111) in sulfate-containing electrolytes: a theoretical and experimental study

We study the underpotential deposition of Cu on single-crystal Au(111) electrodes in sulfate-containing electrolytes by a combination of computational statistical-mechanics based lattice-gas modeling and experiments. The experimental methods are in situ cyclic voltammetry and coulometry and ex situ Auger electron spectroscopy and low-energy electron diffraction. The experimentally obtained voltammetric current and charge densities and adsorbate coverages are compared with the predictions of a two-component lattice-gas model for the coadsorption of Cu and sulfate. This model includes effective, lateral interactions out to fourth-nearest neighbors. Using group-theoretical ground-state calculations and Monte Carlo simulations, we estimate effective electrovalences and lateral adsorbate--adsorbate interactions so as to obtain overall agreement with experiments, including both our own and those of other groups. In agreement with earlier work, we find a mixed R3xR3 phase consisting of 2/3 monolayer Cu and 1/3 monolayer sulfate at intermediate electrode potentials, delimited by phase transitions at both higher and lower potentials. Our approach provides estimates of the effective electrovalences and lateral interaction energies, which cannot yet be calculated by first-principles methods.Comment: 36 pages, 14 Postscript figures are in uufiles for

Electrodeposited mesh-type dimensionally stable anode for oxygen evolution reaction in acidic and alkaline media

© 2019A mesh-type dimensionally stable anode (DSA) consisting of ruthenium and iridium with low catalyst loading was prepared as an oxygen evolution reaction catalyst in acidic and alkaline media. The electrodeposition (ED) conditions, i.e., applied current density and total cycle number, and ED solutions with different precursor ratios of ruthenium to iridium are examined to fabricate various DSAs with a uniform thickness, and the effect of the iridium content on the catalytic activity is investigated. Among various DSA electrodes, the DSA electrode without iridium exhibits the highest activity and stability in the acidic medium owing to the high ratio of ruthenium. Conversely, the DSA electrode obtained using the ED solution with the ratio of 8:2 exhibits the highest performance in the alkaline medium. This is because the DSA electrode without iridium showed low stability, which is attributed to the dissolution of ruthenium oxide in the alkaline medium. In addition, two large-scale DSA electrodes optimized in the acidic and alkaline electrolytes show excellent performance, indicating the feasibility of the application of this electrode in practical electrolysis11sciescopu

Enhancement of service life of polymer electrolyte fuel cells through application of nanodispersed ionomer

Copyright © 2020 The Authors, some rights reserved.In polymer electrolyte fuel cells (PEFCs), protons from the anode are transferred to the cathode through the ionomer membrane. By impregnating the ionomer into the electrodes, proton pathways are extended and high proton transfer efficiency can be achieved. Because the impregnated ionomer mechanically binds the catalysts within the electrode, the ionomer is also called a binder. To yield good electrochemical performance, the binder should be homogeneously dispersed in the electrode and maintain stable interfaces with other catalyst components and the membrane. However, conventional binder materials do not have good dispersion properties. In this study, a facile approach based on using a supercritical fluid is introduced to prepare a homogeneous nanoscale dispersion of the binder material in aqueous alcohol. The prepared binder exhibited high dispersion characteristics, crystallinity, and proton conductivity. High performance and durability were confirmed when the binder material was applied to a PEFC cathode electrode11sciescopu

Modulatory effect of ginseng total saponins on dopamine release and tyrosine hydroxylase gene expression induced by nicotine in the mouse

Abstract Several studies have demonstrated that behavioral activation induced by psychostimulants is prevented by ginseng total saponin (GTS), which has been known to act on the central dopaminergic system. In an attempt to investigate whether the effect of GTS is through its inhibitory action on the elevated dopaminergic transmission, we examined the effect of GTS on nicotine-induced dopamine (DA) release in the nucleus accumbens (NA) of freely moving rats using in vivo microdialysis. Systemic injection of nicotine (3 mg/kg; i.p.) produced a mild increase in extracellular DA of dialysates samples in the NA (132 913% over basal levels at the peak). GTS (100 mg/kg; i.p.) had no effect on resting levels of extracelluar DA. However, an increase in accumbens DA release produced by systemic nicotine was completely blocked by systemic pre-treatment with GTS (100 mg/kg; i.p.). In addition, the effect of GTS on nicotine-induced tyrosine hydroxylase (TH) and immediate early gene expression in ventral tegmental area (VTA) or NA regions was examined. A single injection of nicotine increased TH mRNA level at VTA region. GTS, which did not affect the basal TH mRNA expression, attenuated nicotine-induced TH mRNA expression. Nicotine slightly increased both c-fos and c-jun mRNA level and GTS, which did not affect the basal c-fos and c-jun mRNA expression, further enhanced nicotine-induced c-fos and c-jun mRNA level at both VTA and NA regions. Our results suggest that GTS may have an inhibitory action against nicotine-induced DA release in NA region and TH mRNA expression in VTA region. GTS may exert an potentiative effect on both c-fos and c-jun mRNA expression at NA region through inhibiting the release of DA in NA

Schisandrae Fructus ethanol extract ameliorates inflammatory responses and articular cartilage damage in monosodium iodoacetate-induced osteoarthritis in rats

Schisandrae Fructus, the fruit of Schisandra chinensis (Turcz.) Baill., is widely used in traditional medicine for the treatment of a number of chronic diseases. Although, Schisandrae Fructus was recently reported to attenuate the interleukin (IL)-1β-induced inflammatory response in chondrocytes in vitro, its protective and therapeutic potential against osteoarthritis (OA) in an animal model remains unclear. Therefore, we investigated the effects of the ethanol extract of Schisandrae Fructus (SF) on inflammatory responses and cartilage degradation in a monosodium iodoacetate (MIA)-induced OA rat model. Our results demonstrated that administration with SF had a tendency to attenuate MIA-induced damage of articular cartilage as determined by a histological grade of OA. SF significantly suppressed the production of pro-inflammatory cytokines such as interleukin (IL)-1β, IL-6, and tumor necrosis factor-α in MIA-induced OA rats. SF also effectively inhibited expression of inducible nitric oxide (NO) synthase and cyclooxygenase-2, thereby inhibiting the release of NO and prostaglandin E2. In addition, the elevated levels of matrix metalloproteinases-13 and two biomarkers for diagnosis and progression of OA, such as cartilage oligomeric matrix protein and C-telopeptide of type II collagen, were markedly ameliorated by SF administration. These findings indicate that SF could be a potential candidate for the treatment of OA

Design and synthesis of multigrain nanocrystals via geometric misfit strain.

The impact of topological defects associated with grain boundaries (GB defects) on the electrical, optical, magnetic, mechanical and chemical properties of nanocrystalline materials1,2 is well known. However, elucidating this influence experimentally is difficult because grains typically exhibit a large range of sizes, shapes and random relative orientations3-5. Here we demonstrate that precise control of the heteroepitaxy of colloidal polyhedral nanocrystals enables ordered grain growth and can thereby produce material samples with uniform GB defects. We illustrate our approach with a multigrain nanocrystal comprising a Co3O4 nanocube core that carries a Mn3O4 shell on each facet. The individual shells are symmetry-related interconnected grains6, and the large geometric misfit between adjacent tetragonal Mn3O4 grains results in tilt boundaries at the sharp edges of the Co3O4 nanocube core that join via disclinations. We identify four design principles that govern the production of these highly ordered multigrain nanostructures. First, the shape of the substrate nanocrystal must guide the crystallographic orientation of the overgrowth phase7. Second, the size of the substrate must be smaller than the characteristic distance between the dislocations. Third, the incompatible symmetry between the overgrowth phase and the substrate increases the geometric misfit strain between the grains. Fourth, for GB formation under near-equilibrium conditions, the surface energy of the shell needs to be balanced by the increasing elastic energy through ligand passivation8-10. With these principles, we can produce a range of multigrain nanocrystals containing distinct GB defects