Safety evaluation of rechargeable cells with lithium metal anodes and amorphous V2O5 cathodes

Rechargeable cells with lithium metal anodes have a very large theoretical energy density and are a promising cell system. However, rechargeable lithium metal cells are not yet currently commercially available. One of the biggest problems with the cells is the poor safety aspect resulting from the high chemical reactivity of lithium. We have been studying a cell system consisting of an amorphous (a-)V2O5P2O5 (95:5 in molar ratio) cathode, a lithium (Li) metal anode and an organic electrolyte in fabricating an AA-size prototype. In this paper, we report recent progress on our rechargeable lithium metal cell focusing on its safety.     

Direct Observation of Internal Structure in Spray-Dried Alumina Granules

The internal structure of spray-dried alumina granules was characterized by optical microscopy by immersing them in a liquid having a refractive index close to that of alumina. This method provides a unique technique for the detailed analysis of the internal structure of spray-dried granules.     

Reaction and diffusion of reactive disperse dye in nylon 6

The diffusion of a reactive disperse dye with a vinylsulfonyl group accompanied by simultaneous reaction with the amino end groups in nylon 6 was examined by the method of cylindrical film roll at 70°C and pH 2.2–8.0. The experimental diffusion profiles of the active and fixed species of the dye in nylon 6 were confirmed to be described by the diffusion equation accompanied by the chemical reaction with substrate taking the limited amount of the end groups into account, where the active species of dye were assumed to react only with the free base of amino end groups. The completion of the reaction with the amino end groups was observed in the first layer from the surface at pH 6.0–8.0. The value of diffusion coefficient was constant (8.0 × 10^?10 cm²/s) at all the pH's. The product of the second-order rate constant, k₂, of reaction of the dye and the dissociation constant, K_a, of the amino end groups was constant (k₂K_a = 4.0 × 10^?9 s^?1) at pH 2.2–8.0. The k₂ values of the reaction with various substrates for vinylsulfonyl and monochlorotriazinyl-reactive dyes were compared and the practical dyeing conditions were discussed.     

Mechanical properties of DLC films prepared inside of micro-holes by pulse plasma CVD

Diamond-like carbon (DLC) films are metastable amorphous carbon materials with superior tribological characteristics. In order to improve wear resistance of micro-extrusion dies with numerous imperceptible holes, DLC films were deposited on the inner wall surface of model dies with holes of 2 and 0.9 mm in diameter, and 20 mm in depth by using pulse plasma CVD method. This paper will discuss how argon gas, deposition pressure and time affect the characteristics of films deposited on the inner wall surface of dies. This micro-coating method can be applied widely for inner wall surface treatment of components with thin holes.     

Glyme-based nonaqueous electrolytes for rechargeable lithium cells

Poly(ethylene glycol)dimethyl ethers [(CH₃O(CH₂CH₂O)_nCH₃, n = 1, 2, 3, and 4)] are generally known as “glymes”. This study examines the conductivity, lithium ion solvation state and charge-discharge cycling efficiency of lithium metal anodes in glyme-based electrolytes for rechargeable lithium cells. 1 M (M: mol l⁻¹) LiPF₆ was used as the solute. The properties of the glymes were investigated by using a ternary mixed solvent consisting of n-glyme, ethylene carbonate (EC) and methylethylcarbonate (MEC). This was because the solubility of LiPF₆ is far less than 1 M in an n-glyme single solvent. The glyme solutions exhibited higher conductivity and higher lithium cycling efficiency than EC/MEC. The conductivity tended to increase with decreases in ethylene oxide chain number (n) and solution viscosity. The decrease in the solution viscosity resulted from the change in the lithium ion solvation structure that occurred when a glyme was added to EC/MEC. The selective solvation of the glyme with respect to lithium ions was clearly demonstrated by -NMR measurements. The lithium cycling efficiency value depended on the charge-discharge current (I_ps). When n increased there was an increase in lithium cycling efficiency at a low I_ps and a decrease in the reduction potential of the glymes. When the conductivities including those at low temperature (below 0 °C), and charge-discharge cycling at a high current are taken into account, di- or tri-glyme is superior to the other glymes tested here.     

Investigation of CH4 Reforming with CO2 on Meso-Porous Al2O3-Supported Ni Catalyst

Meso-porous Al₂O₃-supported Ni catalysts exhibited the highest activity, stability and excellent coke-resistance ability for CH₄ reforming with CO₂ among several oxide-supported Ni catalysts (meso-porous Al₂O₃ (Yas1-2, Yas3-8), -Al₂O₃, -Al₂O₃, SiO₂, MgO, La₂O₃, CeO₂ and ZrO₂). The properties of deposited carbons depended on the properties of the supports, and on the meso-porous Al₂O₃-supported Ni catalyst, only the intermediate carbon of the reforming reaction formed. XRD and H₂-TPR analysis found that mainly spinel NiAl₂O₄ formed in meso-porous Al₂O₃ and -Al₂O₃-supported catalysts, while only NiO was detected in -Al₂O₃, SiO₂, CeO₂, La₂O₃ and ZrO₂ supports. The strong interaction between Ni and meso-porous Al₂O₃ improved the dispersion of Ni, retarded its sintering and improved the activated adsorption of CO₂. The coking reaction via CH₄ temperature-programed decomposition indicated that meso-porous Al₂O₃-supported Ni catalysts were less active for carbon formation by CH₄ decomposition than Ni/-Al₂O₃ and Ni/-Al₂O₃.     

A Novel KCaNi/α-Al2O3 Catalyst for CH4 Reforming with CO2

A potassium and calcium co-promoted nickel catalyst (KCaNi/-Al₂O₃) prepared by a direct impregnation method possessed a high activity, high stability and excellent coke resistance properties in CH₄ reforming with CO₂. XRD, XPS and H₂-TPR characterizations indicated that (i) Ca and K strengthened the interaction between Ni and -Al₂O₃ and promoted the formation of a unique NiAl₂O₄ phase on the surface of the catalyst and (ii) Ca and K increased the dispersion of Ni and retarded its sintering. Coking reactions (CH₄ temperature-programmed decomposition and O₂-TPO) disclosed that K reduced carbon formation via CH₄ decomposition.     

Preparation and properties of transparent cellulose hydrogels

Highly transparent cellulose hydrogels with physical crosslinkage were prepared from nonaqueous organic cellulose solutions and viscose by coagulating and regenerating cellulose in an aqueous solution containing a water‐miscible organic solvent. Nonaqueous organic cellulose solutions used were LiCl/dimethylacetamide, paraformaldehyde/dimethyl sulfoxide, and triethylammonium chloride/dimethyl sulfoxide. Preparation conditions and physical properties of the transparent cellulose hydrogels were studied. The transparency of the cellulose hydrogels depended on the composition of the aqueous solution containing the organic solvent. Furthermore, transparent cellulose hydrogels from viscose showed high tensile strength. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3020–3025, 2003     

Synthesis and characterization of CeO2 nano-rods

We report a synthesis of two types of CeO₂ nano-rods via the facile and efficient hydrothermal process free from any surfactant and template. The synthesized nano-rods are chemically identified as CeO₂ with the standard fluorite structure but their morphologies are different. The nano-rods prepared with cerium nitrate hexahydrate and sodium phosphate are thicker and shorter with diameter of ∼30 nm and length of ∼100 nm, and those prepared with cerium acetate hydrate and dibasic sodium phosphate are thinner and longer with ∼10 nm in diameter and ∼400 nm in length. Microstructural analyses reveal that the two species of nano-rods have low-energy {111} surfaces and grow along the 〈112〉 direction. As a consequence of their morphologies, the two types of synthesized nano-rods exhibit excellent UV-absorption ability in comparison to the irregular CeO₂ nanoparticles.