Arrays of sealed silicon nanotubes as anodes for lithium ion batteries.

Silicon is a promising candidate for electrodes in lithium ion batteries due to its large theoretical energy density. Poor capacity retention, caused by pulverization of Si during cycling, frustrates its practical application. We have developed a nanostructured form of silicon, consisting of arrays of sealed, tubular geometries that is capable of accommodating large volume changes associated with lithiation in battery applications. Such electrodes exhibit high initial Coulombic efficiencies (i.e., >85%) and stable capacity-retention (>80% after 50 cycles), due to an unusual, underlying mechanics that is dominated by free surfaces. This physics is manifested by a strongly anisotropic expansion in which 400% volumetric increases are accomplished with only relatively small (<35%) changes in the axial dimension. These experimental results and associated theoretical mechanics models demonstrate the extent to which nanoscale engineering of electrode geometry can be used to advantage in the design of rechargeable batteries with highly reversible capacity and long-term cycle stability.

Optically bifacial thin-film wire-grid polarizers with nano-patterns of a graded metal-dielectric composite layer.

We report on the concept of a thin film wire-grid polarizer (WGP) with optically dual characteristics by introducing a nano-patterned graded metal-dielectric composite-material layer. The Ti-SiO(2) composite layer with a depth profile of a gradually-varied composition ratio shows an absorptive feature due to the elimination of an optical interface between a metal and a glass substrate, while the metal side of the WGP gives a reflective character. The unprecedented optically-bifacial thin-film WGP with the 144 nm-period straight-line patterns of a 100 nm-thick Ti-SiO(2) composite layer and a 185 nm-thick Al layer shows the exceptionally low reflectance below 15 % from the absorptive side and the high polarization extinction ratio (PER) of over 500 at 550 nm, which is acceptable for use as various display applications such as AMOLEDs and LCDs.

Weak-microcavity organic light-emitting diodes with improved light out-coupling.

We propose and demonstrate weak-microcavity organic light-emitting diode (OLED) displays with improved light-extraction and viewing-angle characteristics. A single pair of low- and high-index layers is inserted between indium tin oxide (ITO) and a glass substrate. The electroluminescent (EL) efficiencies of discrete red, green, and blue weak-microcavity OLEDs are enhanced by 56%, 107%, and 26%, respectively, with improved color purity. Moreover, full-color passive-matrix bottom-emitting OLED displays are fabricated by employing low-index layers of two thicknesses. As a display, the EL efficiency of white color was 27% higher than that of a conventional OLED display.

Dispersion properties of aqueous-based LiFePO4 pastes and their electrochemical performance for lithium batteries.

Aqueous-based LiFePO(4) pastes to fabricate the cathode of lithium-ion battery were investigated with an emphasis on chemical control of suspension component interactions among LiFePO(4) particulates, carbon black, carboxymethyl cellulose (CMC), and poly(acrylic acid) (PAA). The dispersion properties of LiFePO(4) were characterized using electroacoustic, flow behavior and green microstructural observation. Correlation was made between the dispersion properties and electrochemical performance of the particles. It was found that the addition of PAA significantly decreases the viscosity of the LiFePO(4) paste. The decrease of viscosity leads to increasing the solid concentration, which affects the electrochemical properties. The electrochemical characteristics of formulated pastes were evaluated using coin-type half cells. Although there is no significant difference between coin cells fabricated with CMC only and CMC/PAA combination in electrochemical cycling test, the dispersion properties of pastes indicate that the electrode fabricated with CMC/PAA, potentially, has much improved discharge capacity compared to that with CMC alone because of the possibility to increase active mass portion in electrode paste.