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Izumi Nakai

Bio: Izumi Nakai is an academic researcher from Tokyo University of Science. The author has contributed to research in topics: X-ray absorption fine structure & Crystal structure. The author has an hindex of 41, co-authored 234 publications receiving 6948 citations. Previous affiliations of Izumi Nakai include University of Education, Winneba & Lucideon.


Papers
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Journal ArticleDOI
TL;DR: Electrochemical oxidation/reduction 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 consistent with the mechanism proposed in the literature related to the Li-excess manganese layered oxides.
Abstract: Lithium-excess manganese layered oxides, which are commonly described by the chemical formula zLi2MnO3−(1 − z)LiMeO2 (Me = Co, Ni, Mn, etc.), are of great importance as positive electrode materials for rechargeable lithium batteries. In this Article, LixCo0.13Ni0.13Mn0.54O2−δ samples are prepared from Li1.2Ni0.13Co0.13Mn0.54O2 (or 0.5Li2MnO3−0.5LiCo1/3Ni1/3Mn1/3O2) 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 ...

1,053 citations

Journal ArticleDOI
TL;DR: Layered NaNi(0.5)Mn(0.)5)O(2) (space group: R ̅3m), having an O3-type (α-NaFeO( 2) type) structure according to the Delmas' notation, is prepared by a solid-state method and electrochemical reactivity is examined.
Abstract: Layered NaNi0.5Mn0.5O2 (space group: R3m), having an O3-type (α-NaFeO2 type) structure according to the Delmas’ notation, is prepared by a solid-state method. The electrochemical reactivity of NaNi0.5Mn0.5O2 is examined in an aprotic sodium cell at room temperature. The NaNi0.5Mn0.5O2 electrodes can deliver ca. 105–125 mAh g–1 at rates of 240–4.8 mA g–1 in the voltage range of 2.2–3.8 V and show 75% of the initial reversible capacity after 50 charge/discharge cycling tests. In the voltage range of 2.2–4.5 V, a higher reversible capacity of 185 mAh g–1 is achieved; however, its reversibility is insufficient because of the significant expansion of interslab space by charging to 4.5 V versus sodium. The reversbility is improved by adding fluoroethylene carbonate into the electrolyte solution. The structural transition mechanism of Na1–xNi0.5Mn0.5O2 is also examined by an ex situ X-ray diffraction method combined with X-ray absorption spectroscopy (XAS). The staking sequence of the [Ni0.5Mn0.5]O2 slabs chang...

573 citations

Journal ArticleDOI
17 Dec 1998-Nature
TL;DR: It is shown that Atlantic and Pacific eels collected in the ocean have spent their entire lifetime there and have never migrated into fresh water, indicating that freshwater eels need not be catadromous, and that populations from the sea contribute primarily to future recruitment.
Abstract: The catadromous migration of freshwater eels, in which they migrate from freshwater streams to the sea to spawn1, 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

333 citations

Journal ArticleDOI
TL;DR: In this article, a carbon-coated Na2FePO4F was synthesized by a simple solid-state method with ascorbic acid as carbon source, which achieved an initial discharge capacity of 110 mAh g-1 at a rate of 1/20 C (6.2

228 citations

Journal ArticleDOI
15 May 2009
TL;DR: In this article, Li and NaNi0.5Mn 0.5O2 and NaCrO2 electrodes were investigated in 1 mol dm-3 NaClO4 propylene carbonate at room temperature.
Abstract: 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.

203 citations


Cited by
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01 Jan 1989
TL;DR: In this article, trace-element data for mid-ocean ridge basalts and ocean island basalts are used to formulate chemical systematics for oceanic basalts, interpreted in terms of partial-melting conditions, variations in residual mineralogy, involvement of subducted sediment, recycling of oceanic lithosphere and processes within the low velocity zone.
Abstract: Summary Trace-element data for mid-ocean ridge basalts (MORBs) and ocean island basalts (OIB) are used to formulate chemical systematics for oceanic basalts. The data suggest that the order of trace-element incompatibility in oceanic basalts is Cs ≈ Rb ≈ (≈ Tl) ≈ Ba(≈ W) > Th > U ≈ Nb = Ta ≈ K > La > Ce ≈ Pb > Pr (≈ Mo) ≈ Sr > P ≈ Nd (> F) > Zr = Hf ≈ Sm > Eu ≈ Sn (≈ Sb) ≈ Ti > Dy ≈ (Li) > Ho = Y > Yb. This rule works in general and suggests that the overall fractionation processes operating during magma generation and evolution are relatively simple, involving no significant change in the environment of formation for MORBs and OIBs. In detail, minor differences in element ratios correlate with the isotopic characteristics of different types of OIB components (HIMU, EM, MORB). These systematics are interpreted in terms of partial-melting conditions, variations in residual mineralogy, involvement of subducted sediment, recycling of oceanic lithosphere and processes within the low velocity zone. Niobium data indicate that the mantle sources of MORB and OIB are not exact complementary reservoirs to the continental crust. Subduction of oceanic crust or separation of refractory eclogite material from the former oceanic crust into the lower mantle appears to be required. The negative europium anomalies observed in some EM-type OIBs and the systematics of their key element ratios suggest the addition of a small amount (⩽1% or less) of subducted sediment to their mantle sources. However, a general lack of a crustal signature in OIBs indicates that sediment recycling has not been an important process in the convecting mantle, at least not in more recent times (⩽2 Ga). Upward migration of silica-undersaturated melts from the low velocity zone can generate an enriched reservoir in the continental and oceanic lithospheric mantle. We propose that the HIMU type (eg St Helena) OIB component can be generated in this way. This enriched mantle can be re-introduced into the convective mantle by thermal erosion of the continental lithosphere and by the recycling of the enriched oceanic lithosphere back into the mantle.

19,221 citations

Journal ArticleDOI
TL;DR: This paper will describe lithium batteries in more detail, building an overall foundation for the papers that follow which describe specific components in some depth and usually with an emphasis on the materials behavior.
Abstract: In the previous paper Ralph Brodd and Martin Winter described the different kinds of batteries and fuel cells. In this paper I will describe lithium batteries in more detail, building an overall foundation for the papers that follow which describe specific components in some depth and usually with an emphasis on the materials behavior. The lithium battery industry is undergoing rapid expansion, now representing the largest segment of the portable battery industry and dominating the computer, cell phone, and camera power source industry. However, the present secondary batteries use expensive components, which are not in sufficient supply to allow the industry to grow at the same rate in the next decade. Moreover, the safety of the system is questionable for the large-scale batteries needed for hybrid electric vehicles (HEV). Another battery need is for a high-power system that can be used for power tools, where only the environmentally hazardous Ni/ Cd battery presently meets the requirements. A battery is a transducer that converts chemical energy into electrical energy and vice versa. It contains an anode, a cathode, and an electrolyte. The anode, in the case of a lithium battery, is the source of lithium ions. The cathode is the sink for the lithium ions and is chosen to optimize a number of parameters, discussed below. The electrolyte provides for the separation of ionic transport and electronic transport, and in a perfect battery the lithium ion transport number will be unity in the electrolyte. The cell potential is determined by the difference between the chemical potential of the lithium in the anode and cathode, ∆G ) -EF. As noted above, the lithium ions flow through the electrolyte whereas the electrons generated from the reaction, Li ) Li+ + e-, go through the external circuit to do work. Thus, the electrode system must allow for the flow of both lithium ions and electrons. That is, it must be both a good ionic conductor and an electronic conductor. As discussed below, many electrochemically active materials are not good electronic conductors, so it is necessary to add an electronically conductive material such as carbon * To whom correspondence should be addressed. Phone and fax: (607) 777-4623. E-mail: stanwhit@binghamton.edu. 4271 Chem. Rev. 2004, 104, 4271−4301

5,475 citations

Journal ArticleDOI
26 Mar 2013-ACS Nano
TL;DR: The properties and advantages of single-, few-, and many-layer 2D materials in field-effect transistors, spin- and valley-tronics, thermoelectrics, and topological insulators, among many other applications are highlighted.
Abstract: Graphene’s success has shown that it is possible to create stable, single and few-atom-thick layers of van der Waals materials, and also that these materials can exhibit fascinating and technologically useful properties. Here we review the state-of-the-art of 2D materials beyond graphene. Initially, we will outline the different chemical classes of 2D materials and discuss the various strategies to prepare single-layer, few-layer, and multilayer assembly materials in solution, on substrates, and on the wafer scale. Additionally, we present an experimental guide for identifying and characterizing single-layer-thick materials, as well as outlining emerging techniques that yield both local and global information. We describe the differences that occur in the electronic structure between the bulk and the single layer and discuss various methods of tuning their electronic properties by manipulating the surface. Finally, we highlight the properties and advantages of single-, few-, and many-layer 2D materials in...

4,123 citations