Anomalously High Ionic Conductivity of Li2SiS3-Type Conductors.

Solid-state electrolytes that exhibit high ionic conductivities at room temperature are key materials for obtaining the next generation of safer, higher-specific-energy solid-state batteries. However, the number of currently available crystal structures for use as superionic conductors remains limited. Here, we report a lithium superionic conductor, Li2SiS3, with tetragonal crystal symmetry, which possesses a new three-dimensional framework structure consisting of isolated edge-sharing tetrahedral dimers. This species exhibits an anomalously high ionic conductivity of 2.4 mS cm-1 at 298 K, which is 3 orders of magnitude higher than the reported ionic conductivity for its orthorhombic polymorph. The framework of this conductor consists mainly of silicon, which is abundant in natural resources, and its further optimization may lead to the development of new solid-state electrolytes for large-scale applications.

Effect of interlayer spacing on the electrochemical properties of alkali titanate nanotubes.

Multilayered titanate nanotubes (TNTs) has been considered as a candidate for lithium ion battery anode material. However, it has a problem of high irreversible capacity due to trapped lithium ions in the interlayer space. To solve this problem, an attempt to enlarge the interlayer spacing has been made in this work to improve intercalation characteristics of TNTs. Monoatomic ions in hydrothermally heat-treated TNTs were substituted to one of Li, Na and K alkali ions via ion-exchange process. The TNTs (200) interlayer spacing peak in XRD patterns showed a shift to a lower angle, indicating an enlarged interlayer spacing of TNTs. The Li-, Na- and K-ion exchanged TNTs exhibited an initial capacity of 214, 230 and 248 mA h/g at 0.1 C, respectively, in the TNTs // LiPF6 electrolyte // Li metal coin type cell test. It was found that the enlarged interlayer spacing resulted in an increment in the specific capacity and rate capability. This increase was attributed to both the enhanced lithium ion diffusion and the increased number of lithium ion intercalation sites in the TNTs interlayers.

Characterization of La(0.8)Sr(0.2)MnO(3 +/-delta) nanopowders synthesized by aerosol flame synthesis for SOFC cathode.

Lanthanum strontium manganite (La(0.8)Sr(0.2)MnO(3 +/- delta), LSM) powders with a high specific surface area (55.26 m2/g) were successfully synthesized by aerosol flame synthesis (AFS) technique. The crystallinity and morphology of the synthesized powders sintered at various temperatures were studied by XRD, TEM and BET. The synthesized powders exhibited spherical shape mostly in a few nanometer ranges with a relatively high crystallinity due to thermal plasma reactions in a high temperature of oxy-hydrogen flame. To analyze electrochemical performances of synthesized LSM powders, impedance spectroscopy (IS) was carried out with the symmetric cells prepared by slurry based electrostatic spray deposition (ESD) onto the YSZ electrolyte pellet. The interfacial polarization resistances were 3.04 ohms cm2 at 750 degrees C which is relatively lower than that of micro-porous film (7.24 ohms cm2) applying micro-sized powders deposited on same condition.

Effects of sodium content of titanate nanotubes on lithium battery performance.

Titanate nanotubes were prepared by hydrothermal process of powder for the application to the anode of lithium batteries. After the synthesis of titanate nanotubes by the chemical treatment with 10 M NaOH solution, the quantity of sodium remnant was controlled by the HCl washing solutions of different pH of 1, 4, 7, 10 and 13. The prepared titanate nanotubes had outer and inner diameter of 9 nm and 6 nm, and the interlayer spacing of about 1 nm. The amount of sodium remnant was investigated using Inductively Coupled Plasma (ICP) Atomic Emission Spectrometer, and the variation of structure and morphology with the contents of the sodium was studied by X-ray diffraction (XRD), Thermogravimetric Analysis (TGA), Field Emission Scanning Electron Microscopy (FE-SEM) and High Resolution Transmission Electron Microscopy (HR-TEM). Coin cells composed of (Titanate nanotubes//1 M LiPF6-EC/DEC//Li metal) were prepared for studying the basic charging-discharging behavior and electrochemical properties of the prepared titanate nanotubes with controlled sodium contents. The effects of the remnant sodium content on the microstructures, morphology and electrochemical properties of titanate nanotubes will be discussed.