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First-Principles Study on the Thermal Stability of LiNiO2 Materials Coated by Amorphous Al2O3 with Atomic Layer Thickness

2015-05-31T15:00:00Z

Title: First-Principles Study on the Thermal Stability of LiNiO2 Materials Coated by Amorphous Al2O3 with Atomic Layer Thickness Author(s): Kang, Joonhee; Han, Byungchan Abstract: Using first-principles calculations, we study how to enhance thermal stability of high Ni compositional cathodes in Li-ion battery application. Using the archetype material LiNiO2 (LNO), we identify that ultrathin coating of Al2O3 (0001) on LNO(012) surface, which is the Li de-/intercalation channel, substantially improves the instability problem. Density functional theory calculations indicate that the Al2O3 deposits show phase transition from the corundum-type crystalline (c-Al2O3) to amorphous (a-Al2O3) structures as the number of coating layers reaches three. Ab initio molecular dynamic simulations on the LNO(012) surface coated by a-Al2O3 (about 0.88 nm) with three atomic layers oxygen gas evolution is strongly suppressed at T = 400 K. We find that the underlying mechanism is the strong contacting force at the interface between LNO(012) and Al2O3 deposits, which, in turn, originated from highly ionic chemical bonding of Al and O at the interface. Furthermore, we identify that thermodynamic stability of the a-Al2O3 is even more enhanced with Li in the layer, implying that the protection for the LNO(012) surface by the coating layer is meaningful over the charging process. Our approach contributes to the design of innovative cathode materials with not only high-energy capacity but also long-term thermal and electrochemical stability applicable for a variety of electrochemical energy devices including Li-ion batteries. © 2015 American Chemical Society.

Preferential Positioning of gamma-Ray Treated Multi-Walled Carbon Nanotubes in Polyamide 6,6/Poly(p-phenylene ether) Blends

2013-03-31T15:00:00Z

Title: Preferential Positioning of gamma-Ray Treated Multi-Walled Carbon Nanotubes in Polyamide 6,6/Poly(p-phenylene ether) Blends Author(s): Mun, Sung Cik; Kim, Mokwon; Lee, Choon Soo; Lee, Min Hee; Son, Younggon; Park, O. Ok Abstract: Morphological characteristics and electrical conductivity of polyamide 6,6/poly(p-phenylene ether)/multi-walled carbon nanotube (PA66/PPE/MWCNT) ternary nanocomposites were investigated. The MWCNTs were modified by 60Co gamma ray (γ-ray) irradiation under a dry condition and O2 atmosphere, which introduces oxygen-containing functional groups on the surfaces of the MWCNTs and thereby provides better compatibility with the hydrophilic PA66 phase. It was observed that the MWCNTs are preferentially positioned in the continuous PA66 matrix, whereas PPE domains are almost free of MWCNTs. Since PA66 consists of a continuous phase and the MWCNTs are preferentially positioned in the PA66 phase, electrical conductivity of PA66/PPE/MWCNT ternary composites is higher than that of PA66/MWCNT binary composites at the same MWCNT content. It was observed that raising the processing temperature and increasing the mixing time were effective means of improving the electrical conductivity of the composites, via enhancement of MWCNT dispersion. [Figure not available: see fulltext.] © 2013 The Polymer Society of Korea and Springer Sciene+Business Media Dordrecht.

Immunosensor Based on Electrogenerated Chemiluminescence Using Ru(bpy)32+-Doped Silica Nanoparticles and Calix[4]crown-5 Self-Assembled Monolayers

2013-03-31T15:00:00Z

Title: Immunosensor Based on Electrogenerated Chemiluminescence Using Ru(bpy)32+-Doped Silica Nanoparticles and Calix[4]crown-5 Self-Assembled Monolayers Author(s): Kim, Yang-Rae; Seo, Hyo-Ju; Oh, Jeong-Wook; Lim, Hyunchang; Kim, Tae Hyun; Kim, Hasuck Abstract: An electrogenerated chemiluminescence (ECL)-based immunosensor for the detection of immunoglobulin G (IgG) has been fabricated using Ru(bpy)3 2+-doped silica nanoparticles and calix[4]crown-5 self-assembled monolayers (SAMs). Ru(bpy)3 2+-doped silica nanoparticles are prepared by the water-in-oil (W/O) microemulsion method. ProLinker B, a commercially available thiolated calix[4]crown-5 derivative, is utilized for the immobilization of anti-immunoglobulin G (Anti-IgG) on a gold electrode. The concentration of IgG is measured using a sandwich-type ECL immunosensor based on the proposed immunosensor. The ECL intensity is linearly proportional to the IgG concentration over the concentration range 5-30μgmL-1. The detection limit of IgG is 1.5μgmL-1. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Preparation and characterization of novel polyimide-silica hybrids

2013-03-31T15:00:00Z

Title: Preparation and characterization of novel polyimide-silica hybrids Author(s): Akhter, Toheed; Saeed, Shaukat; Siddiqi, Humaira Masood; Park, O. Ok Abstract: Polyimide-silica (PI-SiO2) hybrids were prepared from a novel polyimide (PI), derived from pyromellitic dianhydride (PMDA), 1,6-bis(4-aminophenoxy)hexane (synthesized) and 4,4′-oxydianiline. SiO2 networks (5-30wt%) were generated through sol-gel process using either tetraethylorthosilicate (TEOS) or a mixture of 3-aminopropyltriethoxysilane-PMDA-based coupling oligomers (APA) and TEOS. Thin, free standing hybrid films were obtained from the respective mixtures by casting and curing processes. The hybrid films were characterized using Fourier transform infrared, 29Si nuclear magnetic resonance (NMR), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectrometry and atomic force microscopy (AFM) techniques. 29Si NMR results provide information about formation of organically modified silicate structures that were further substantiated by FE-SEM and AFM micrographs. Contact angle measurements and thermogravimetric thermograms reveal that the addition of APA profoundly influences surface energy, interfacial tension, thermal stability and the residual char yield of modified hybrids in comparison to those obtained by mixing only TEOS. It was found that reduced particle size, efficient dispersion and improved interphase interactions were responsible for the eventual property enhancement. © 2012 John Wiley & Sons, Ltd.