Hideki Iba

Hydrogen absorption and modulated structure in Ti–V–Mn alloys

Abstract In order to apply hydrogen-absorbing alloys to new energy carrier uses, such as hydrogen storage tanks or Ni–MH batteries, a drastic increase in the hydrogen capacity of these alloys is required. For years, intermetallic compounds or single-phase alloys have been studied as hydrogen-absorbing materials. New approaches to alloy design, relating to multiphase alloys, are proposed and verified. These approaches help to identify a new structure on a multiphase alloy. As a result, a new hydrogen-absorbing alloy, consisting of a nano-structure having a large hydrogen capacity and good desorbing properties, was found.

The relation between microstructure and hydrogen absorbing property in Laves phase-solid solution multiphase alloys

Abstract The multiphase alloy Zr 0.5 Ti 0.5 VMn, that is assumed to consist of the b.c.c. solid solution phase and the AB 2 type Laves phase, is designed as a variation of the ‘Laves phase related b.c.c. solid solution’. Observations of microstructure show that Zr 0.5 Ti 0.5 VMn consists of three phases: matrix C14, colonies of b.c.c. and small particle of α-ZrO 2 . In pressure-composition isotherms, a linear combination of hydrogen storage capacity and fraction of phases in Zr 0.5 Ti 0.5 VMn is found at any equilibrium pressure studied. Crystal structure and composition of each phase are investigated by combination of TEM-EDX and X-ray Rietveld analysis to discuss the relation between the Laves phase and the b.c.c. solid solution.

Crystal structure and phase composition of alloys Zr1−xTix(Mn1−yVy)2

Abstract The crystal structure and morphology of the Laves-phase alloys Zr 1 − x Ti x (Mn 1 − y V y ) 2 , have been studied by X-ray powder diffraction and transmission electron microscopy (TEM). Hydriding properties were analyzed from pressure-composition (PC) isotherms. Most of the alloys were multiphase, with up to four phases simultaneously present in one alloy. The identified phases were: hexagonal C14 and cubic C15 Laves phases, bcc solid solution, α -ZrO 2 and η-carbide-type oxide. A qualitative phase map of the system was constructed. TEM measurements indicated that the Laves phase C14 and the bcc solid solution have preferential atomic composition. To clarify this result, the alloys Zr 0.6 Ti 0.4 Mn 1.1 V 0.9 and Ti 0.2 Mn 0.2 V 0.6 were prepared and analyzed by X-ray powder diffraction. The hydrogen capacity on the system Zr 1 − x Ti x MnV by PC measurements agreed with the value calculated by the capacity and abundance of each end member phase.

Cation ordering in A-site-deficient Li-ion conducting perovskites La(1−x)/3LixNbO3

Cation-deficient perovskites exhibit complex local atomic arrangements which cannot be adequately described by average crystal structure models. By combining reciprocal-space electron diffraction analysis and direct observations of atom positions using state-of-the-art scanning transmission electron microscopy, we clarify the nature of the cation ordering within A-site-deficient perovskite single crystals of La(1−x)/3LixNbO3 (x = 0 and x = 0.04). Both materials are found to have complex modulated crystal structures with two types of A-cation ordering, namely a long-range layer ordering in alternate (001)p planes and a short-range (intra-domain) columnar ordering within La-rich (001)p layers. The columnar ordering (occupational modulation) produces modulated displacements of Nb and O atoms. It is also found that substitution of even a small amount of Li for La can affect significantly the columnar ordering, leading to a series of structural and microstructural changes that are likely to have a deleterious effect on the Li-ion conductivity of this material.

Electrochemical Li+ insertion capabilities of Na4−xCo3(PO4)2P2O7 and its application to novel hybrid-ion batteries

Electrochemically Na+-extracted Na4−xCo3(PO4)2P2O7 exhibits both Li+ and Na+ insertion capabilities. Given these compatibilities, novel hybrid-ion batteries were demonstrated by combining a Na4Co3(PO4)2P2O7 positive electrode and Li4Ti5O12 negative electrode in a lithium-based electrolyte.

A highly efficient Li2O2 oxidation system in Li–O2 batteries

A novel indirect charging system that uses a redox mediator was demonstrated for Li-O2 batteries. 4-Methoxy-2,2,6,6-tetramethylpiperidinyl-1-oxyl (MeO-TEMPO) was applied as a mediator to enable the oxidation of Li2O2, even though Li2O2 is electrochemically isolated. This system promotes the oxidation of Li2O2 without parasitic reactions attributed to electrochemical charging and reduces the charging time.

Atomic level changes during capacity fade in highly oriented thin films of cathode material LiCoPO4

High-quality thin films with well-defined fast lithium ion diffusion pathways and minimal structural discontinuities are needed to develop high-performance electrodes for all-solid-state Li-ion batteries. Achieving this requires an understanding of the electrochemical processes and structural changes that take place within an electrode during charge/discharge. Here we report the successful synthesis of highly oriented olivine-structured LiCoPO4 thin films by chemical solution deposition onto Au(111)/Al2O3(0001) substrates. State-of-the-art scanning transition electron microscopy (STEM) and theoretical simulations are used to examine surface structures and the changes that occur during electrochemical cycling. As-synthesised films are found to be composed of nearly defect-free domains that are predominantly aligned with (210), (010) or (101) surfaces parallel to the substrate. High-angle annular dark field (HAADF)-STEM revealed the formation of considerable numbers of cation exchange (antisite) defects in the surface regions after only three cycles. Upon further electrochemical cycling, significant capacity fade, together with an increase in the concentration of cation exchange defects, was observed. Electron energy loss spectroscopy (EELS) revealed that formation of these defects is associated with oxygen loss and deformation of PO4 tetrahedra, leading to structural degradation detrimental to the electrochemical performance of thin-film LiCoPO4 electrodes.

Solid-State Lithium-Ion Batteries for Electric Vehicles

Abstract Rapid global industrial development, rising populations and the corresponding increase in the number of vehicles have caused a sudden jump in the consumption of fossil fuel energy. Given this background, the critical issues facing vehicle manufactures can be summarized into the following three: preventing air pollution, reducing CO2 emissions and developing vehicles that can run on a variety of alternative energy sources to petroleum. The most effective way of addressing these issues is considered to be the development of vehicles that can run on electricity, such as hybrid vehicles, plug-in hybrid vehicles, electric vehicles and fuel-cell hybrid vehicles.

Anisotropy of ionic conduction in single-crystal Li x La(1− x )/3NbO3 solid electrolyte grown by directional solidification

The anisotropy of ionic conduction in a solid electrolyte (Li x La(1− x )/3NbO3) was experimentally confirmed for the first time. Ionic conduction measurements were carried out on the (100), (010), (001), (110), (111), and (112) planes of single-crystal ingots of Li x La(1− x )/3NbO3 grown by directional solidification. We found that the ionic conductivity in Li x La(1− x )/3NbO3 with x = 0.08 was 3.6 × 10−4 S cm−1 in the [100] and [010] directions, approximately 10 times higher than that in the [001] direction. Such anisotropy of the ionic conduction is discussed with respect to the characteristic layered structure of Li x La(1− x )/3NbO3.

Study of New Active Materials for Rechargeable Sodium-Ion Batteries

Na4Co3(PO4)2P2O7 is the unique crystal structure with multiple sodium-ion pathways in the structure. The electrochemical properties of Na4Co3(PO4)2P2O7 as a positive electrode for sodium-ion batteries were investigated. Na4Co3(PO4)2P2O7 had the multi redox couples in the highest potential region between 4.1 V and 4.7 V among ever reported sodium active materials and could deliver the reversible capacity of ca. 95 mAhg-1, corresponding to ca. 2.2 Na+. Na4Co3(PO4)2P2O7 also exhibited the high rate capabilities and had a small polarization in the charge - discharge profile even at the high current densities, resulting in high energy efficiency of the battery. These performances indicate Na4Co3(PO4)2P2O7 can be one of the good candidates for a positive electrode material of sodium-ion batteries.