Izumi Nakai

Detailed Studies of a High-Capacity Electrode Material for Rechargeable Batteries, Li2MnO3−LiCo1/3Ni1/3Mn1/3O2

Lithium-excess manganese layered oxides, which are commonly described by the chemical formula zLi(2)MnO(3)-(1-z)LiMeO(2) (Me = Co, Ni, Mn, etc.), are of great importance as positive electrode materials for rechargeable lithium batteries. In this Article, Li(x)Co(0.13)Ni(0.13)Mn(0.54)O(2-δ) samples are prepared from Li(1.2)Ni(0.13)Co(0.13)Mn(0.54)O(2) (or 0.5Li(2)MnO(3)-0.5LiCo(1/3)Ni(1/3)Mn(1/3)O(2)) by an electrochemical oxidation/reduction process in an electrochemical cell to study a reaction mechanism in detail before and after charging across a voltage plateau at 4.5 V vs Li/Li(+). Changes of the bulk and surface structures are examined by synchrotron X-ray diffraction (SXRD), X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), and time-of-flight secondary ion mass spectroscopy (SIMS). SXRD data show that simultaneous oxygen and lithium removal at the voltage plateau upon initial charge causes the structural rearrangement, including a cation migration process from metal to lithium layers, which is also supported by XAS. This is consistent with the mechanism proposed in the literature related to the Li-excess manganese layered oxides. Oxygen removal associated with the initial charge on the high voltage plateau causes oxygen molecule generation in the electrochemical cells. The oxygen molecules in the cell are electrochemically reduced in the subsequent discharge below 3.0 V, leading to the extra capacity. Surface analysis confirms the formation of the oxygen containing species, such as lithium carbonate, which accumulates on the electrode surface. The oxygen containing species are electrochemically decomposed upon second charge above 4.0 V. The results suggest that, in addition to the conventional transition metal redox reactions, at least some of the reversible capacity for the Li-excess manganese layered oxides originates from the electrochemical redox reaction of the oxygen molecules at the electrode surface.

Do all freshwater eels migrate

The catadromous migration of freshwater eels, in which they migrate from freshwater streams to the sea to spawn, is widely accepted. The proportion of time spent in freshwater and ocean habitats can be determined by studying the ratio of strontium (Sr) and calcium (Ca) in the otoliths (ear-stones) of the eels. Here we use this technique to show that Atlantic and Pacific eels collected in the ocean have spent their entire lifetime there and have never migrated into fresh water. This finding indicates that freshwater eels need not be catadromous, and that populations from the sea contribute primarily to future recruitment.

Electrochemically Reversible Sodium Intercalation of Layered NaNi0.5Mn0.5O2 and NaCrO2

Electrochemical activities of NaNi0.5Mn0.5O2 and NaCrO2, having the analogous layered structure to LiCoO2, were investigated in 1 mol dm-3 NaClO4 propylene carbonate at room temperature. Almost all sodium ions were extracted from the NaNi0.5Mn0.5O2 and NaCrO2 electrodes by galvanostatic oxidation to 4.5 V accompanied with several phase transitions. Layered NaNi0.5Mn0.5O2 electrode showed a highly reversible capacity of 185 mAh g-1 as positive electrode in Na cell in the potential region between 2.5 and 4.5 V versus Na. A NaCrO2 electrode was hardly electroactive after oxidation up to 4.5 V. When galvanostatic cycling was carried in the limited potential domain between 2 and 3.5 V, both electrodes showed discharge capacities of 100 - 120 mAh g-1 with satisfactory capacity retention. Layered LiCrO2 (R-3m) and NaCrO2 (R-3m) possess the quite similar crystal structures and the same transition metal, nevertheless they were inactive and active in Li and Na cells, respectively.

Electrochemical and In Situ XAFS-XRD Investigation of Nb2O5 for Rechargeable Lithium Batteries

Nb 2 O 5 exhibits various crystal systems, such as orthorhombic (o), tetragonal (t), and monoclinic (m), among which Nb 2 O 5 synthesized at 900-1000°C is commercially used as a cathode material of the 2-V lithium ion battery. The battery performances depended on the structure of Nb 2 O 5 , and the t-Nb 2 O 5 synthesized at 1000°C exhibited an excellent cycling performance with a large discharge capacity of 190 mAh (g oxide) -1 . The structural variations of Nb 2 O 5 during electrochemical reaction were examined. The in situ synchrotron radiation-X-ray diffraction (XRD) measurement indicated that o- and t-Nb 2 O 5 maintain their original crystal lattices, accompanying a small change in the cell volume even after the Li intercalation. The in situ X-ray absorption fine structure (XAFS) analysis of o- and t-Nb 2 O 5 revealed that the continuous variation from Nb 5+ to Nb 4+ took place during the intercalation process. A significant rearrangement of the Nb-O octahedra accompanied by the change of Nb-O and Nb-Nb interactions occurred in both structures with Li intercalation. XRD and XAFS data suggests that the two-dimensional layer structure of t-Nb 2 O 5 seems to be more flexible regarding the Li intercalation compared with the three-dimensional structure of o-Nb 2 O 5 . This may account for the better cyclic performance of the former material as the electrode material.

Exfoliated Nanosheet Crystallite of Cesium Tungstate with 2D Pyrochlore Structure: Synthesis, Characterization, and Photochromic Properties

Layered cesium tungstate, Cs(6+x)W(11)O(36), with two-dimensional (2D) pyrochlore structure was exfoliated into colloidal unilamellar sheets through a soft-chemical process. Interlayer Cs ions were replaced with protons by acid exchange, and quaternary ammonium ions were subsequently intercalated under optimized conditions. X-ray diffraction (XRD) measurements on gluelike sediment recovered from the colloidal suspension by centrifugation showed a broad pattern of a pronounced wavy profile, which closely matched the square of calculated structure factor for the single host layer. This indicates the total delamination of the layered tungstate into nanosheets of Cs(4)W(11)O(36)(2-). Microscopic observations by transmission electron microscopy and atomic force microscopy clearly revealed the formation of unilamellar crystallites with a very high 2D anisotropy, a thickness of only approximately 2 nm versus lateral size up to several micrometers. In-plane XRD analysis confirmed that the 2D pyrochlore structure was retained. The colloidal cesium tungstate nanosheet showed strong absorption of UV light with sharp onset, suggesting a semiconducting nature. Analysis of the absorption profile provided 3.6 eV as indirect band gap energy, which is 0.8 eV larger than that of the bulk layered precursor, probably due to size quantization. The nanosheet exhibited highly efficient photochromic properties, showing reversible color change upon UV irradiation.

X-ray absorption fine structure and neutron diffraction analyses of de-intercalation behavior in the LiCoO2 and LiNiO2 systems

Abstract Variations of electronic and local structures of Ni and Co in Li1 − xNiO2 and Li1 − xCoO2 as a function of x were clarified for the first time by in situ X-ray absorption fine structure analysis (XAFS). Chemical shifts of the X-ray absorption near edge sructure spectra of the Ni K-edge in Li1 − xNO2 as a function of x were continuous while an abrupt change was observed for the Co K-edge spectra of Li1 − xCoO. Radial structure functions obtained by Fourier-transform of the Ni K-edge EXAFS of LiNiO2 exhibited abnormally low height of the Ni-O peak. This phenomenon is explained by the Jahn—Teller distortion of the NiO6 octahedron due to the low spin Ni3+ (d7) ion. De-intercalation of the Li ion caused oxidation of Ni3+ (d7) to Ni4+ (d6) and reduced the distortion, hence the Ni-O peak increased with increasing x value. The crystal structures of LiNiO2 treated with D2O, and electrochemically de-intercalated Li0.34NiO2 were solved by Rietveld analysis of neutron diffraction data.

Single Crystal X-Ray Structure Analysis of Bi2(Sr, Ca)2CuOx and Bi2(Sr, Ca)3Cu2Ox Superconductors

Average crystal structures of Bi2(Sr, Ca)2CuOx and Bi2(Sr, Ca)3Cu2Ox were analyzed using single crystal X-ray intensity data applying anisotropic temperature factors. Crystal data: Bi2Sr1.60Ca0.40CuO6, Bbmb, a=5.3826(8) A, b=5.3761(11), c=24.384(7), Rw=0.108 for 282 reflections; Bi2.06Sr1.70Ca1.24Cu2O8, Bbmb, a=5.3946(8), b=5.3895(13), c=30.649(12), Rw=0.064 for 354 reflections. Precession photographs show that Bi2Sr1.60Ca0.40CuO6 has a monoclinic modulated structure and Bi2.06Sr1.70Ca1.24Cu2O8 has an orthorombic one. The incommensurate modulated structures were qualitatively illustrated by using a modulation wave model.

In vivo analysis of metal distribution and expression of metal transporters in rice seed during germination process by microarray and X-ray Fluorescence Imaging of Fe, Zn, Mn, and Cu

To investigate the flow of the metal nutrients iron (Fe), zinc (Zn), manganese (Mn), and copper (Cu) during rice seed germination, we performed microarray analysis to examine the expression of genes involved in metal transport. Many kinds of metal transporter genes were strongly expressed and their expression levels changed during rice seed germination. We found that metal transporter genes such as ZIP family has tendency to decrease in their expressions during seed germination. Furthermore, imaging of the distribution of elements (Fe, Mn, Zn, and Cu) was carried out using Synchrotron-based X-ray microfluorescence at the Super Photon ring-8 GeV (SPring-8) facility. The change in the distribution of each element in the seeds following germination was observed by in vivo monitoring. Iron, Mn, Zn, and Cu accumulated in the endosperm and embryos of rice seeds, and their distribution changed during rice seed germination. The change in the patterns of mineral localization during germination was different among the elements observed.

Cobalt valence states and origins of ferromagnetism in Co doped TiO2 rutile thin films

Co doped rutile thin films were fabricated on α-Al2O3 (10-12) substrates by laser molecular beam epitaxy. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy indicated that the rutile thin films are (101) oriented and have smooth surfaces with no impurity phases. Co K-edge x-ray absorption near-edge structure, extended x-ray absorption fine structure, and x-ray photoelectron spectroscopy revealed the coexistence of different valence states of Co in the film. Magnetic circular dichroism studies suggest that the observed ferromagnetism is uniform and is related to the electron band structure of TiO2 rutile. Contribution of oxidized (Co2+) and metallic (Co0) cobalt to the ferromagnetism is discussed.

Detection of Uranium and Chemical State Analysis of Individual Radioactive Microparticles Emitted from the Fukushima Nuclear Accident Using Multiple Synchrotron Radiation X-ray Analyses

Synchrotron radiation (SR) X-ray microbeam analyses revealed the detailed chemical nature of radioactive aerosol microparticles emitted during the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, resulting in better understanding of what occurred in the plant during the early stages of the accident. Three spherical microparticles (∼2 μm, diameter) containing radioactive Cs were found in aerosol samples collected on March 14th and 15th, 2011, in Tsukuba, 172 km southwest of the FDNPP. SR-μ-X-ray fluorescence analysis detected the following 10 heavy elements in all three particles: Fe, Zn, Rb, Zr, Mo, Sn, Sb, Te, Cs, and Ba. In addition, U was found for the first time in two of the particles, further confirmed by U L-edge X-ray absorption near-edge structure (XANES) spectra, implying that U fuel and its fission products were contained in these particles along with radioactive Cs. These results strongly suggest that the FDNPP was damaged sufficiently to emit U fuel and fission products outside the containment vessel as aerosol particles. SR-μ-XANES spectra of Fe, Zn, Mo, and Sn K-edges for the individual particles revealed that they were present at high oxidation states, i.e., Fe(3+), Zn(2+), Mo(6+), and Sn(4+) in the glass matrix, confirmed by SR-μ-X-ray diffraction analysis. These radioactive materials in a glassy state may remain in the environment longer than those emitted as water-soluble radioactive Cs aerosol particles.