Motoya Kanda

Hydrogen storage properties of new ternary system alloys: La2MgNi9, La5Mg2Ni23, La3MgNi14

The hydrogen storage properties of the new ternary system alloys, La2MgNi9, La5Mg2Ni23, La3MgNi14, were investigated. As a result, the negative electrode of the La5Mg2Ni23 alloy (La0.7Mg0.3Ni2.8Co0.5) showed a large discharge capacity (410 mAh/g), 1.3 times larger than that of AB5 type alloys. These ternary system alloys were found to be mainly composed of stacked AB5 and AB2 structure subunits in a superstructure arrangement.

Synthesis and properties of LiNiO2 as cathode material for secondary batteries

The optimum preparation condition and electrochemical properties of LiNiO2 as the cathode material for lithium secondary batteries were investigated. LiNiO2 samples were prepared from Li(OH)2·H2O and Ni(OH)2 in the range from 500 to 900 °C. The compound prepared in an oxygen atmosphere at 700 °C exhibited the highest discharge capacity of 200 mAh/g in the voltage range from 3.0 to 4.3 V. The structure and charge-transfer resistance of the Li1−xNiO2 compound were examined at each state-of-charge by X-ray diffractometry and a.c. impedance spectroscopy. The charge-transfer resistances were low in the range of 0.15<x<0.75, which was related to the expansion of the interlayer distance between NiO2 layers.

Effect of Partial Substitution on Hydrogen Storage Properties of Mg2Ni Alloy

The effect of partial substitution on the hydrogen storage properties of Mg{sub 2}Ni was investigated. It was found that as a result of substitution of Mg with a more electronegative element (Al or Mn), absorption of hydrogen easily occurs at lower temperature. The alloy powder prepared with a mechanical grinding method was also studied. This alloy powder was found to be mainly changed to an amorphous-like state by this treatment. Consequently, the negative electrode of the mechanically ground Mg{sub 2}Ni alloy shows a large discharge capacity, 750 mAh/g, which is two and one-half times that of AB{sub 5} type alloys. It was also found that the hydrogen reversibility of the mechanically ground Mg{sub 1.9}A{sub 0.1}Ni alloy electrode remarkably increased.

The Hydrogen Storage Properties of New Mg2Ni Alloy

The hydrogen storage properties of a novel Mg{sub 2}Ni alloy powder prepared with a mechanical grinding method were investigated. This alloy powder was transformed to an amorphous-like state by this treatment. As a result, an electrode of this alloy shows a large discharge capacity (750 mAh/g) which is 2.5 times higher than that of AB{sub 5}-type alloys. This significant improvement of hydrogen storage properties seems to be achieved by the increase in the crystal boundary and a heterogeneous strain in this alloy. The hydrogen equilibrium pressure of this alloy increased markedly.

Lithium insertion and extraction for high-capacity disordered carbons with large hysteresis

Disordered carbons heat-treated from 550 to 1000 °C containing hydrogen atoms showed high specific capacities with large hysteresis in the potential when used as anodes in lithium-ion cells. The lithium storage mechanism in the disordered carbons has been investigated by the charge-discharge test, X-ray diffraction (XRD) and solid-state 7Li NMR measurements. Variation of the layer spacing of the disordered carbon heat-treated at 900 °C with insertion and extraction indicated that lithium was inserted into the unorganized carbon site (U-site) near 0 V vs LiLi+ after insertion into the layer structure site (L-site) and removed from the U-site near 1 V after the extraction from the L-site. 7Li NMR spectra of the lithiated disordered carbons heat-treated at 550 °C showed two bands with a relatively small shift (< 10 ppm) from 0 ppm vs LiCl, indicating that stored lithium had an ionic character. The results of 7Li NMR analysis revealed the existence of the ionic lithium stored in the reversible storage sites and lithium trapped in the irreversible storage site. The high capacity with large hysteresis was attributed to the ionic lithium stored on the condensed aromatic ring in the U-site.

Synthesis and electrochemical properties for LiNiO2 substituted by other elements

Abstract Li 1 − x Ni 1 − x O 2 − y F y as the cathode materials for rechargeable lithium batteries were synthesized by co-substitution of nickel sites and oxygen sites for LiNiO 2 . The materials were found to possess good properties on charge/discharge cycling without significant deterioration of the initial capacity. In order to investigate the reason the cycle properties were improved, we performed experiments focusing on the crystallographic point of view using X-ray diffractometry accompanied by electrochemical property. These materials were found to restrain none of crystallographic change during charge/discharge regardless of the amount of substitution. According to the charge/discharge curve, the materials indicate relatively low internal impedance. Thus, the main reason for the improvements of the cycle properties may be caused by mechanism which has no direct relation to the above crystallographic change.

Electrochemical properties of mechanically ground Mg2Ni alloy

The electrochemical properties of Mg 2 Ni type alloy powder prepared with a mechanical grinding (MG),of Mg 2 Ni and Ni or Pd powders were investigated. This alloy powder was found to be mainly changed to an amorphous-like matrix with dispersed nano-size Ni or Pd particles by the MG treatment. As a result, the negative electrode of the mechanically ground Mg 2 Ni alloy with Ni showed a large discharge capacity (830 mAh/g) which is 2.5 times larger than that of AB 5 type alloys. In the mechanically ground Mg 2 Ni alloy with Pd, the cycle life of the alloy electrode was considerably improved. The effect of partial substitution on the hydrogen storage properties of Mg 2 Ni was also investigated. It was found that the hydrogen reversibility of the mechanically ground Mg 1.9 M 0.1 Ni (M=Al, B, C, Ag) alloy electrode was remarkably improved by the substitution of Mg with more electronegative elements.

Large Hysteresis during Lithium Insertion into and Extraction from High‐Capacity Disordered Carbons

Perylene-based disordered carbon (PBDC) heat-treated at 550 °C for anodes in Li-ion cells showed large hysteresis and a high reversible capacity of 800 mAh/g. The hysteresis was analyzed by polarization and impedance measurements. The overpotential during lithium extraction increased markedly in the range of open-circuit potential, 0.5-1 V vs Li/Li + . The impedance spectra of PBDC during lithium insertion were significantly different from those during extraction. The charge-transfer resistance for lithiated PBDC during extraction above 0.5 V was much larger than that for the PBDC during insertion. The chemical diffusion coefficient of lithium, D Li , of PBDC during lithium insertion decreased almost linearly from 5 x 10 -10 to 3 x 10 -12 cm 2 s -1 with increasing lithium storage capacity. The values of D Li during lithium extraction above 0.5 V were much smaller than those during insertion. The large hysteresis was due to the large charge-transfer resistance and the slow diffusion of lithium during lithium extraction from the fully lithiated PBDC. The large charge-transfer resistance during lithium extraction has been interpreted as the rectification of lithiated PBDC, which is similar to that of n-type semiconductors under anodic polarization

Hydrogen storage properties of La(Ni0.9M0.1)3 alloys

Abstract The hydrogen storage properties of LaNi 3 -type hydrogen storage alloys were investigated in order to increase the capacity of rechargeable nickel–metal hydride batteries. By partially substituting a foreign metal at Ni sites, the discharge capacity of La(Ni 0.9 M 0.l ) 3 (M=Al, Fe, Mn, Si, Sn, Cu) alloy electrodes could be increased at room temperature. In particular, La(Ni 0.9 Al 0.l ) 3 and La(Ni 0.9 Mn 0.l ) 3 alloy electrodes showed significantly higher hydrogen storage capacities and markedly better reversibilities than LaNi 3 .

High-capacity lithium-ion cells using graphitized mesophase-pitch-based carbon fiber anodes

Abstract We have developed high-capacity lithium-ion cells using graphitized mesophase-pitch-based carbon fiber (MCF) as an anode material. The graphitized MCF is a highly graphitized carbon fiber with a radial-like texture in the cross section. This structure contributes to the rapid diffusion of lithium ions inside the carbon fiber. The diffusion coefficient of lithium ions in the graphitized MCF was one order of magnitude larger than those for graphite, resulting in an excellent high-rate performance of the carbon electrode. The graphitized MCF anode showed larger capacity, a higher rate capability, and better reversibility than the graphite anode. The 863448 size (8.6 mm × 34 mm × 48 mm) prismatic cell with the graphitized MCF anode exhibited a large capacity of > 1000 mAh. At 3 A discharge, the prismatic cell had 95% of its capacity at 0.5 A discharge with a mid-discharge voltage of 3.35 V. The cell maintained > 85% of its initial capacity after 500 cycles and showed high capacity at −20 °C. It has thus been demonstrated that the prismatic cell using the graphitized MCF anode has excellent performance, and is an attractive choice for the power sources of cellular phones and other appliances.