Mika Eguchi

Low-temperature preparation of lithium vanadium oxides by solution processing

Lithium vanadium (Li--V) oxides were prepared by solution processing using the reaction of an aqueous hydrogen peroxide solution with lithium and vanadium alkoxides, LiO-n-C 3 H 7 and VO(O-i-C 3 H 7 ) 3 . It was found that various phases of the Li-V oxides such as the orthorhombic 2D-V 2 O 5 compound, and the β- and γ-phases having the general formula of Li x V 2 O 5 (0≤x<2.2) are obtained at low temperature such as ∼300 °C. Particularly, it should be noted that γ-Li x -V 2 O 5 can be prepared as a single phase in the x range of 1.3-2.2. The charge and discharge behavior for the γ-phase material (x=2.2) is discussed as compared to that of the γ-phase material (x=1) prepared by conventional high temperature solid-state reaction.

Preparation and electrochemical properties of the layered material of LixVyO2 (x=0.86 and y=0.8)

Layered lithium-vanadium oxide with a composition of LixVyO2 (x = 0.86 and y = 0.8) was prepared by the hydrothermal reaction of V2O3 with LiOH center dot H2O at 180 degrees C. This material corresponds to a layered rhombohedral structure related to alpha-NaFeO2 in which the vanadium ions are disordered in alternate layers of octahedral 3a (0, 0, 0) and 3b (0, 0, 1/2) sites. The electrochemical properties of this Li0.86V0.8O2 material were investigated and compared with those of the layered Li0.96VO2 made by the conventional solid-state reaction. It was found that the electrochemical capacity and reversibility of the Li0.86V0.8O2 material are significantly improved compared to those of the Li0.96VO2 material; the reversible specific capacities of the Li/Li0.86V0.8O2 and Li/Li0.96VO2 systems are similar to 100 and similar to 50 mAh g(-1), respectively, under the current densities of 7.14 mA g(-1) over 20 charge-discharge cycles with a potential window of 1.50-4.50 V. Such a reversibility results from the structural stability of Li0.86V0.8O2, whereas the increase in the reversible specific capacity can be qualitatively interpreted in terms of the presence of vanadium vacancies in the structure. (c) 2005 The Electrochemical Society.

Lithium insertion into (V1−yMoy)2O5

The effects of structural modification caused by substitution of Mo for a part of V in V 2 O 2 on structural changes upon lithium insertion were investigated. For this purpose (V 1-y Mo y ) 2 O 5 (y = 0.25) was synthesized, and its insertion behavior and structural changes upon lithium insertion were analyzed by XRD and ESR methods. In (V 0.75 Mo 0.25 ) 2 O 5 , the phases except for the starting material were not observed upon lithium insertion, and no phase transformation characteristics of V 2 O 5 occurred. From ESR measurement, a broad singlet signal of V(IV) was found, but those of Mo(V) were not detected. The line width of the signal V(IV) increased steeply at 0.7 < x < 1. The open circuit potentials became less noble with increasing x, and dropped steeply at 0.7 < x < 1. These dependencies closely correlate with structural changes estimated from results of ESR and XRD analyses. At 2.7 < x, ω-phase oxide was formed.

Interfacial Nanostructure of the Polymer Electrolyte Fuel Cell Catalyst Layer Constructed with Different Ionomer Contents

Fibrous carbon materials such as carbon nanotubes (CNTs) and carbon nanofilaments (CNFs) have attracted attention for use in the polymer electrolyte fuel cells (PEFCs). We have applied one type of fibrous carbon materials named Marimo carbon (MC) as the catalyst support. The modified nanocolloidal method was used preparing the Marimo carbon supported Pt catalyst (Pt/MC). And then, ionomer/carbon ratio in the cathode catalyst layer of the PEFC has been investigated for its effect on performance and structure of the membrane electrode assembly (MEA). The morphologies and cell performance of cathode catalyst layer using Marimo carbon changed dramatically with ionomer content. In case of excess ionomer, the air volume between CNFs was plugged up by ionomer, and blocked supply fuel gas diffusion caused decrease cell performance. PEFC cell performance was increase with decreasing ionomer content.